GENOME WIDE ASSOCIATION STUDY AND GENOMIC HERITABILITY OF ANTIMULLERIAN HORMONE IN DAIRY HOLSTEIN HEIFERS By Muhammad Yasir Nawaz A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Animal Science-Master of Science 2017 ABSTRACT GENOME WIDE ASSOCIATION STUDY AND GENOMIC HERITABILITY OF ANTIMULLERIAN HORMONE IN DAIRY HOLSTEIN HEIFERS By Muhammad Yasir Nawaz The objectives of this study were to estimate the genomic heritability of Anti Mullerian hormone (AMH), identify candidate genes associated with AMH production, and establish phenotypic correlations between serum AMH concentrations and parameters of reproductive performance in Holstein heifers. AMH concentrations were determined in 2905 dairy Holstein heifers. Animals were genotyped using the Zoetis 70K SNP Panel. Genotypes were imputed to standard USDA 60,671 bovine SNP set with 54,519 SNP markers remaining after standard editing procedures. A linear mixed model was used to model the random effects of sampling day and genomics on the logarithm of AMH. Results showed that the genomic heritability (±SEM) of AMH was 0.36±0.03. We identified significant associations between AMH and 11 SNP markers on chromosome 11 and one marker on chromosome 20 based on a 5% false discovery rate. Some of the annotated genes in those regions have been previously identified as being important for AMH expression and ovarian function. There was no strong evidence of any association between conventional reproductive performance measures of dairy heifers and their serum AMH concentration. It seems that these associations should be studied in later parities as these heifers continue to mature. Nevertheless, the high heritability of AMH and a well-established association of AMH with super ovulatory response may make AMH a biomarker to genetically select cattle for larger gonads, more follicles and better response to superovulation. This thesis is dedicated to my parents, their love and affection has always been a source of strength for me. I dedicate this thesis to my wife, my brothers and my sisters whose continued support motivated me to accomplish everything I have achieved in my life. I also dedicate this work to all my friends and teachers who believed in me and helped me sort out the challenges of graduate school life. iii ACKNOWLEDGMENTS I owe my deepest gratitude to my research adviser Dr. Robert J Tempelman. He encouraged and supported me throughout my degree program. I will forever be thankful to him for being patient, and allowing me to work on my pace while transitioning from the field of Veterinary Medicine to Animal Genetics. It looked too hard for me in the beginning but his leadership, guidance and support helped me to successfully cope up with studies. I would like to thank other members of my research committee, Dr. Ireland always asked the thought provoking questions which improved my ability to think in the realm of genomics in animal reproduction. Dr. Steibel extended his support in developing my skills in R programming and genomic analysis. Dr. Erskine was kind to me in dedicating some time to give inputs regarding the application of my research in dairy industry. I could never have made this far without their guidance. I would like to extend my gratitude to my parents Malik Muhammad Nawaz and Mastooran Nawaz for all their hard work and sacrifices for my education. My biggest motivation to pursue graduate studies was to make them proud of me. Furthermore, I want to extend my deepest appreciation to my wife who sacrificed a lot for my graduate studies. She was always with me through all the stresses of graduate school to support me and ensured that I had the peace of mind to focus on my studies. I am also thankful to my elder brothers Kashif and Wasif, and sister Summayya for their exemplary hard work in the pursuit of education and success in life. They always set high targets for me and created a sense of competition which helped me achieve more in life. I am greatly thankful to my younger siblings Ayesha, Asif and Areej, for their iv unconditional love and support. Whenever I felt down and out, I would talk with them to replenish my energy. I want to extend my gratitude to my fellow graduate students Kaitlyn, Ryan, Scott, Deborah, Yongfang, Sebastian and Chunyu for their help in studies and all the non-academic experiences we shared. I am also thankful to my roommate Azam and close friends at MSU; Faizan, Ali, Salman and Hassan who became my extended family in East Lansing. I am also thankful to my friends in Pakistan Rashid, Usman, Saboor, Burhan, Akhtar, and Sajid who always kept in contact with me, Finally, I would like to thank Fulbright Program Pakistan for giving me the opportunity to pursue graduate studies at MSU. I owe deep gratitude to Institute of International Education (IIE) Program Officer; Stephanie Sasz and administrative staff at MSU; Barb Sweeny and Steve Bursian for handling the administrative aspect of my studies. v TABLE OF CONTENTS LIST OF TABLES……………………………………….…………………………….……… viii LIST OF FIGURES……………………………………………………………………………... ix CHAPTER ONE…………………………………………………….……………………..…….. 1 Introduction……………………………………………………….………………..…….. 2 LITERATURE CITED………………………………………………...…...................... 10 CHAPTER TWO…………………………………………………………………...……...…… 17 Genome wide association analysis and genomic heritability of anti-Mullerian hormone in Holstein dairy heifers…………….………………………………..…………………. 18 ABSTRACT...……………………………………………………………………………18 INTRODUCTION……………………………………………………………………….19 MATERIALS AND METHODS………………………………………….…………......21 AMH assay……………………………………………………………….……....21 Genotyping.……...…………………………………………………………….... 22 Statistical analysis.…...…………………………………………………………..22 Number of QTL per peak………………………………………………………...24 Confidence interval of the QTL peak.………………………………………...…24 Proportion of genetic variance explained by the significant region……………..25 Identification of candidate genes………………………………………………...26 RESULTS………………………………………………………………………..............27 Heritability.………………………………………………………………………27 GWA Study.……………………………………………………………………...29 Number of QTLs.………………………………………………………………...32 Confidence interval of the peak association on Chromosome 11.……………….34 Confidence interval of the peak association on Chromosome 20.……………….35 LD between significant SNPs.…………………………………………………...36 Candidate genes.…………………………………………………………………37 DISCUSSION……………………………………………………………………….…...38 CONCLUSION………………………………………………………………………......42 APPENDIX.……………………………………………………………………………...44 LITERATURE CITED…………………………………………………………..…...….50 CHAPTER THREE…………………………………………………………………………...…60 Relationship of Anti-Mullerian Hormone with Reproductive Traits in Holstein Heifers…………………………………………………………………………............... 61 ABSTRACT.……………………………………………………………………………..61 INTRODUCTION……………………………………………………………………….62 MATERIAL AND METHODS……………………………………………………...…..63 Statistical analysis……………………………………………………...………...64 RESULTS...…………………………………………………………………..……….....66 Probability of conception in embryo recipients.…………………………………66 vi Probability off conception to first service in artificial insemination recipients …66 Overall probability of conception.……………………………………………….67 Probability of abortion.…………………………………………………………..67 Days open.………………………………………………………………………..68 Age at first calving ……………………………………………………………....68 Number of services per conception.……………………………………………...69 DISCUSSION.………………………………………………………………..…..……...70 CONCLUSION…………………………………………………………………..……....72 OVERALL CONCLUSIONS AND FUTURE DIRECTIONS.…………………………73 LITERATURE CITED.……...……………..…………………………………...…….....75 vii LIST OF TABLES Table 2.1: Significant associations from genome wide association analysis of logarithm of AMH in dairy Holstein heifers.………………………………………………………………………....32 Table 2.2: List of genes identified with in the significant region on chromosome 11 and 20...…45 Table 3.1: Cut off values of quartiles for AMH concentration.………………………………….65 Table 3.2: Least square geometric mean AMH concentrations for different reproductive events....………………………………………………………………………………………….67 Table 3.3: Relationship of AMH with probability of conception nested within quartiles.………67 viii LIST OF FIGURES Figure 2.1: Distribution of serum concentration of AMH in dairy Holstein heifers.……………27 Figure 2.2: Distribution of log transformed serum concentration of AMH in dairy Holstein heifers.……………………………………………………………………………………………28 Figure 2.3: Distribution of accuracy of predicted genomic breeding values of AMH using 2905 animals and 54519 markers.……………………………………………………………………..29 Figure 2.4: Manhattan plot of –log10 P values verses genomic location for logarithm of serum concentrations of AMH in dairy Holstein heifers.…...………………………………………..…30 Figure 2.5: Manhattan plot of P values of markers on chromosome 11 for logarithm of serum concentrations of AMH in dairy Holstein heifers…………………………………………….….31 Figure 2.6: Manhattan plot of P values of markers on chromosome 20 for logarithm of serum concentrations of AMH in dairy Holstein heifers………………………………………………..31 Figure 2.7: Manhattan plot after using the peak SNP as a fixed effect.….....………….………..33 Figure 2.8: Manhattan plot of markers on chromosome 11. Markers with in the 99% confidence interval of the most significant SNP are shown in different color.…………………………........34 Figure 2.9: Manhattan plot of markers on chromosome 20. Markers with in the 99% confidence interval of the most significant SNP are shown in different color……………………………….35 Figure 2.10: LD of all SNPs (n=68) within 99% confidence interval of peak SNP on chromosome 11 arranged in increasing order of base pair position. The significant marker is marked in the map………………………………………………………………………..………36 Figure 2.11: LD of all SNPs (n=25) within 99 % confidence interval of peak SNP on chromosome 20 arranged in increasing order of base pair position. The significant marker is marked in the map……………………………………………….……………………………….37 Figure 3.1: Plot of number of days open after first lactation and serum AMH concentration.….68 Figure 3.2: Plot of age at first calving and serum AMH concentration.………...…………...…..79 ix CHAPTER ONE 1 Introduction Dairy farming is a vital part of the global food system and it plays a key role in sustainability of rural areas in particular. Efficiency of dairy farming is an important consideration not only for global food security but also for profitability and hence, the sustainability of dairy farming. Milk production of individual cows depends on their ability to reproduce as the lactation cycle is initiated and renewed by pregnancy. Efficiency of reproduction is the primary determinant of dairy farm profitability because reproductive losses translate into a number of economic losses due to longer calving interval, shorter herd life, higher replacement cost and higher costs of veterinary treatment and drugs. The total loss due to reproductive failure equates to about 2% of the gross production value or 10% of an average dairy farmer's income (Dijkhuizen et al., 1984) . Therefore, farmers emphasize the optimization of reproductive performance of cattle. Reproductive efficiency in dairy cattle has been decreasing, at least until 2005 (García-Ruiz et al., 2016). It was observed that modern dairy cows have lower first service conception rates (Butler, 1998; Lucy, 2001), longer intervals to first ovulation (Marion and Gier, 1967; de Vries and Veerkamp, 2000), higher incidences of anestrus and abnormal luteal phases (de Vries and Veerkamp, 2000), lower blood progesterone concentrations (Lucy et al., 1998), higher multiple ovulation and twinning rates (Fricke and Wiltbank, 1999), and greater embryonic losses (Lucy, 2001). The root causes of poor reproductive performance were a variety of physiological and management factors that had cumulative effects on reproductive efficiency. However, there is some evidence that a genetic antagonism exists between reproductive traits and milk production (Macmillan et al., 1996; Dematawewa and Berger, 1998; Hansen, 2000). The aggressive genetic selection of dairy cattle for increased milk production has been an important contributing factor to the decreased reproductive efficiency in modern cows. Realizing this situation, cattle breeding 2 schemes around the world have been broadened to include reproduction traits in dairy selection indices (Miglior et al., 2005). National genetic evaluation of cows for fertility was started in USA based on daughter pregnancy rates (DPR) (VanRaden et al., 2004). Consequently, an increase in estimated breeding values (EBV) of cows has been observed for DPR (García-Ruiz et al., 2016). However, the rate of gain in EBV of DPR has been slow due to its low heritability (0.04). Animal breeding is defined as the selective breeding of animals for economically important traits. Traditional genetic selection of animals involves extensive phenotype recording of animals and their relatives to determine their EBV. Animals are selected as parents of next generation based on their EBV. This typically requires a long generation interval in dairy due to a long duration of pregnancy and higher age of puberty. There is also a high cost associated with progeny testing programs to calculate EBVs. Genomic prediction (Meuwissen et al., 2001) allows the determination of EBV of animals right after birth by using their genotype information. Genomic prediction assumes that genetic markers or specifically single nucleotide polymorphisms (SNP) are in linkage disequilibrium (LD) with underlying quantitative trait loci (QTL), which have an additive effect in expression of the trait. It focuses on estimating the cumulative effects of markers without testing for their significance. Therefore, we can predict the breeding values of animals without having to wait for them to mature and exhibit the phenotype. Rates of genetic gain have doubled by using genomic selection in cattle, in part because of a decrease in generation interval. However, the rate of genetic gain and the accuracy of genomic prediction also depends on the genomic heritability of the trait under selection. Heritability refers to the proportion of phenotypic variance due to genetic differences in the population. Unfortunately, the heritability of reproductive traits in dairy is very low (Berry et al., 2014). 3 Discovery of novel biomarker traits in genomic selection that have a high heritability and a relatively high genetic correlation with reproductive traits would increase the rate of genetic gain in reproductive potential. While breeding programs use selection approaches based on genetic evaluations to identify phenotypically superior animals, assisted reproductive technologies (ART) such as artificial insemination, in vitro embryo production, and embryo transfer (Smidt and Niemann, 1999), are used to breed cows considered to be genetically superior. Genomic selection and ART are routinely being used by dairy farmers to improve cattle genetics and reproduction (Garcia et al., 2013). However, the success of the reproductive technologies depends on the individual characteristics of the animal. The high variability of animal responses to super-ovulatory treatments coupled with the high cost of treatments, are limiting factors for widespread use of these technologies. If some of this variation can be attributable to genetics, genomic selection may allow an efficient use of ART. Super ovulatory traits (fertilization and blastocyst rate, ovulation rate, total number of embryos per flush, the number of viable embryos per flush etc.) are difficult to measure, are highly invasive, and require expertise in ultrasound scanning, ovum pick up and in vitro fertilization procedure. Endocrine markers of super ovulatory response traits provide an opportunity to select animals more efficiently for ART. Anti Mullerian hormone (AMH) is a potentially useful endocrine indicator of reproductive potential in dairy cattle. In recent studies, the circulating serum concentration of AMH has been found to be associated with antral follicle count (AFC) (Ireland et al., 2008; Rico et al., 2009; Batista et al., 2014). AFC in turn, is positively associated with size of ovary, total number of follicles in ovary, number of oocytes and embryos in response to super ovulation, and higher gonadotropin and progesterone concentration (Ireland et al., 2011). AMH has been identified as 4 an important marker of super ovulatory response (Monniaux et al., 2010; Souza et al., 2015),invitro embryo production (IVEP) in cattle (Guerreiro et al., 2014; Gamarra et al., 2015; Vernunft et al., 2015), and dairy herd longevity (Jimenez-Krassel et al., 2015). There is some evidence that AMH is correlated with fertility traits like maintenance of pregnancy between 30 and 65 days of pregnancy, and pregnancy rate in cows bred following natural estrus (Ribeiro et al., 2014). Furthermore, AMH is increasingly being viewed as an indicator of health. Mossa et al., (2013) showed that calves born to feed restricted mothers had lower AMH concentrations, larger aortic trunk size and high blood pressure as compared to calves born to control cows. Similarly, low AMH levels in men have been associated with cardiovascular disease in men (Dennis et al., 2013). AMH is originally a growth factor, produced from the granulosa cells of pre-antral and small antral follicles in ovary and sertoli cells of testes in males. It is a 140-kDa dimeric glycoprotein hormone which belongs to the transforming growth factor-β (TGF-β) family (Cate et al., 1986). AMH gene in cow (ENSBTAG00000014955) is located on chromosome 7 and ranges from 22,696,978 bp to 22,699,843 bp on the forward strand. The AMH mRNA and protein exist in the granulosa cells of preantral and small antral follicles (Hirobe et al., 1992; Durlinger et al., 2001). In cattle, Rico (2011) showed that AMH is highly expressed in the cumulus cells and the outer layers of the granulosa cells close to the theca in healthy antral follicles while its expression is strongly diminished in atretic follicles, except in the cumulus cells of atretic follicles surrounding the oocyte. Studies involving circulating serum concentrations of AMH have been conducted by various researchers in dairy animals. These concentrations have been reported to be between 60 to 570 pg/ml in Bos taurus heifers and from 60 to 780 pg/ml in Bos indicus heifers (Batista et al., 2014; Guerreiro et al., 2014; Ribeiro et al., 2014). Another study has reported that plasma 5 concentration of AMH is higher in Bos taurus indicus (Zebu cattle) compared to Bos taurus taurus (European cattle) and found that relationship between AMH and reproductive parameters was found to be significantly greater in Zebu compared to European cattle (Stojsin-Carter et al., 2016). These results suggest that genetic background of cattle may impact their AMH levels. AMH was first discovered to play an important role in sex differentiation in the fetal life (Munsterberg and Lovell-Badge, 1991; Lee et al., 2008). It inhibits formation of Mullerian but not Wolffian ducts during embryonic development. Wolffian ducts in turn give rise to parts of the male reproductive system like epididymis and vas deferens. AMH plays an important role in regulation of ovarian follicle growth and development in adults (Tiftik et al., 2016). AMH also prevents initial recruitment and the premature depletion of the follicular population in the ovary (Durlinger et al., 1999) and prevents activation of primordial follicles into the growing follicle pool (Durlinger et al., 2002). AMH may inhibit follicle stimulating hormone (FSH) induced follicular growth because AMH reduces sensitivity of follicles to FSH treatments Durlinger (2001). In the rat ovary, AMH was found to be expressed in pre antral and small antral follicles while absent in large antral follicles (Baarends et al., 1995). Some follicles inherently show lower AMH expression than others and these follicles may be more sensitive to FSH and more prone to be selected by the secondary estrous FSH peak (Visser and Themmen, 2005). As there is a certain FSH threshold level required for follicles to ovulate, different follicles might have a different threshold level due to their inherent differences in AMH expression. Therefore, AMH may play a role in determining which follicles undergo selection and grow and which follicles undergo atresia. In the ovaries of domestic animals, AMH remains constant throughout the estrous cycle. A single blood sample taken on any day of the estrous cycle to measure serum AMH concentration is a 6 reliable phenotypic marker as it is independent of the stage of estrous cycle (Ireland et al., 2011). The concentration of AMH in 4 to 9 years old Holstein dairy cows did not change over a threemonth period (Rico et al., 2009), and measurements of AMH taken before OPU protocols over a period of one year were also significantly correlated with each other (Rico et al., 2012). Several studies in humans also suggest that the concentration of AMH measured through the menstrual cycle does not show significant fluctuations (La Marca et al., 2004; Tsepelidis et al., 2007). Although concentrations may remain very constant within a female, female to female variability does exist. For example, the concentration of AMH varied from 25 to 228 pg/ml (Ireland et al., 2009) and 6 to 433 pg/ml (Ireland et al., 2011). As AMH appears to be greatly variable across individuals, and it has been established as an indicator of reproductive potential in animals, it may be useful for identification of cattle with superior reproductive potential. Genomic prediction relies on the linkage disequilibrium between the SNP markers and the actual causative alleles or “Quantitative Trait Loci” (QTL) which control the expression of a phenotype. As different breeds of animals might have different LD between the markers and QTL, the marker effects estimated in any breed cannot be used to accurately predict the breeding values in another breed (Habier et al., 2007). One possible solution to this problem is to use the causative “Quantitative Trait Nucleotide” (QTN) in selection indexes (Weller and Ron, 2011) instead of relying on the linkage disequilibrium between markers and QTL. This can also facilitate the selection for negatively correlated traits. Selection indexes can incorporate information from markers that have positive QTN effects for one trait but, say, neutral effects for the negatively correlated trait. Furthermore, identification of QTN can also have biotechnological significance as well. Gene editing technologies like CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) can be used in to alter the genotype of an 7 individual to change its phenotypic performance (Cong; et al., 2013). Finally, by extracting functional information about the genes located near the QTL can possibly give rise to a handful of interesting hypotheses on the biological pathways that underlie economically important traits. Genome wide association (GWA) studies are performed as a first step to help locate QTN. GWA studies are designed to detect the association between DNA markers and the traits of interest. Hundreds of GWA analyses have been performed in the last decade on a wide variety of traits in plants, animals and humans. Some of the putative QTLs identified can be validated by previously identified QTNs. For example Cole (2009) showed that the largest marker effects for fat percentage and protein yield were found on BTA14 flanking the diacylglycerol O-acyltransferase 1 (DGAT1) gene (Grisart et al., 2004) and BTA6 flanking the ATP-binding cassette, subfamily G, member 2 gene (Cohen-Zinder et al., 2005) respectively. Other studies have identified novel regions of the genome to search for candidate genes. It has led to new discoveries about genes and pathways involved in common diseases and complex traits (Visscher et al., 2012). For example, DENND1A was identified as a candidate gene for polycystic ovarian condition in human females (Welt et al., 2012). Later functional genomic studies revealed increased expression of DENND1A in theca cells (McAllister et al., 2015). It has been proposed as a diagnostic criterion for polycystic ovarian disease. 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Metab. 97:1342–1347. doi:10.1210/jc.2011-3478. 16 CHAPTER TWO 17 Genome wide association analysis and genomic heritability of anti-Mullerian hormone in Holstein dairy heifers ABSTRACT Anti-Mullerian hormone (AMH) is a growth factor which has an important role in regulation of ovarian follicle growth. Recent studies have shown a positive association between AMH concentrations in serum with the number of follicles and oocytes in ovaries (ovarian reserve), response to superovulation and embryo production, and herd longevity in dairy and beef cattle. The objectives of this study were to estimate the genomic heritability of AMH and identify candidate genes associated with AMH production. AMH concentrations were determined in dairy Holstein heifers. Animals were genotyped using Zoetis 70K SNP Panel. Genotypes were imputed to standard USDA 60,671 bovine SNP set with 54,519 SNP markers remaining after standard editing procedures. A linear mixed model was used to model the random effects of sampling day and genomics on the logarithm of AMH. Results showed that the genomic heritability (±SEM) of AMH was 0.36±0.03. We identified significant associations between AMH and 11 SNP markers on chromosome 11 and one marker on chromosome 20 based on a 5% false discovery rate. Annotated genes in those regions were identified using the ENSEMBL genes database v. 88. of the cow genome (v. UMD 3.1). Some of these genes have been previously reported to be involved in maintenance of cell structure, cell signaling, cell viability, embryonic development of cardiac, gonadal and brain tissues, embryonic survival, oocyte competence, cancer suppression and immunity. The high heritability and a potentially positive association of AMH with some reproductive traits implies that AMH may be used as a biomarker to improve reproductive potential in dairy cattle. 18 INTRODUCTION Reproductive efficiency is vitally important for the profitability of a dairy herd. Aggressive genetic selection of dairy cattle on milk production over the years led to a decrease in genetic merit for reproductive performance (Veerkamp et al., 2001). Reproductive performance was included in the breeding goals around the world only a decade ago. (Miglior et al., 2005). However, the rate of gain in genetic potential observed for reproduction in all these years is slow (García-Ruiz et al., 2016) as the heritability estimates of typical reproductive traits of dairy cattle are low (Berry et al., 2014). Moreover, as reproductive traits are necessarily expressed after puberty, selection decisions cannot be made early in the life of an animal thereby leading to a long generation interval. Reliable biomarkers that are highly correlated with reproductive performance, expressed early in life and are moderately to highly heritable have not been discovered. Such a discovery will be instrumental to identify cattle with superior reproductive potential and design breeding programs for faster genetic gain in reproductive efficiency and hence the profitability of the dairy industry. Anti-Mullerian hormone (AMH) is considered to be a potentially important biomarker of reproductive potential of cattle. It is a growth factor, produced from the granulosa cells of ovary and sertoli cells of testes, and was first discovered to play an important role in sex differentiation in the fetal life (Lee et al., 2008). In adults, AMH regulates ovarian follicle growth (Tiftik et al., 2016). Recent studies have shown a positive association between AMH and dairy herd longevity (Jimenez-Krassel et al., 2015), maintenance of pregnancy, and pregnancy rate in cows bred on estrus (Ribeiro et al., 2014). It is also positively related with in vivo (Monniaux et al., 2010) and in vitro (Guerreiro et al., 2014) embryo production performance of dairy cattle. A single blood sample taken on any day of the estrous cycle to measure serum AMH concentration is a reliable 19 phenotypic marker as it is highly repeatable within an animal and not affected by the stage of estrous cycle. (Ireland et al., 2011). However, AMH appears to be highly variable across individuals. Therefore, it can be useful for identification and subsequently genetic selection of cattle with superior reproductive potential. Genomic prediction allows one to predict the breeding values of animals using their genomic information (Meuwissen et al., 2001). It makes use of the single nucleotide polymorphism (SNP) which is a kind of genetic variation in which a mutation occurs at a single base pair in the deoxy ribo nucleic acid (DNA). Genomic prediction models typically assume that the SNP markers are roughly equally spaced and spread across the whole genome are in linkage disequilibrium (nonrandom association of markers, LD) with the underlying quantitative trait loci (QTL) that control the traits. However, the accuracy of genomic predictions depends on size of the reference population used to derive the prediction equation, the effective population size (which refers to the number of animals contributing as parents of the next generation), the number of SNP markers, the genetic architecture (distribution of the marker effects), and the heritability of the trait (Daetwyler et al., 2008; Goddard, 2009; Meuwissen, 2009). For lowly heritable traits, large number of animals with dense marker information are required for accurate genomic estimated breeding values (GEBV). Genome-Wide Association (GWA) analyses are performed to explore the genetic architecture of a trait i.e. the key genomic regions associated with a trait and the distribution of their effects by identifying the single nucleotide polymorphisms (SNP) significantly associated with the trait. Significant markers from a GWA study may not necessarily be the causal mutations (QTL) themselves, but can be in high LD with the QTL. GWA studies often serve as an important first step to identify the causative QTL. Such GWA studies can suggest candidate genes and formulate new hypothesis for further genetic research. 20 They may also indicate potential drug targets to improve phenotypic performance or cure a disease condition. Marker effects from a GWA study can also be included in genomic prediction models that put additional weight on the certain genomic regions to improve prediction accuracies. However, few GWA studies have been performed for traits associated with dairy cattle fertility (Berry et al., 2014). This study aims to estimate the genomic heritability of AMH and conduct a genome wide association study using the 60k standard USDA SNP panel. MATERIALS AND METHODS All experiments involving cattle were approved by the IACUC at Michigan State University. Holstein heifers (n = 3252, 11-15 months old, located on Green Meadow Farms Inc, Elsie, MI) were subjected once to two intramuscular injections of PGF2α spaced 11 d apart to synchronize estrous cycles. Heifers were synchronized in groups of 95 to 124 heifers once or twice per month for a total number of 29 groups. At 96 h after the last PGF2α injection, a single tail vein blood sample was taken from each heifer to measure serum AMH concentration. Blood samples were taken beginning on 4/18/2014 and ending on 12/4/2015. Follicle hair samples were collected at these times for genotypic analyses. Freemartins (n=144) were not included in the statistical analyses. AMH assay The commercially available anti-Müllerian hormone ELISA serum sample test kit for bovine (MiniTube of America) was used to measure serum AMH concentrations in duplicate 20 ul serum samples in cattle per kit instructions. The two-site AMH assay was validated (Ireland et al., 2008) for use in cattle and does not cross react with other members of the transforming 21 growth factor beta (TGFβ) superfamily including TGFβ, bone morphogenic factor-4 (BMP4), inhibin or activin (Kevenaar et al., 2006). In addition, serum AMH concentrations for five heifers in the study were 75, 55, 1117, 436, 208 pg/ml. When samples from these same individuals were assayed ~12 mo after storage at -80°C, AMH concentrations were 59, 48, 1227, 435, 191 pg/ml, respectively. These results implied that AMH values are relatively stable during long-term storage. Genotyping A total of 2939 Holstein heifers were genotyped for single nucleotide polymorphisms (SNP) using the Zoetis 70K SNP Panel. The genotypes were imputed to standard USDA 60,671 bovine SNP set. SNPs were retained for analysis if they fulfilled the following criteria: missing values < 20%, minor allele frequency (MAF) > 0.05, and pairwise linkage disequilibrium (LD) value of r2 <0.95. The final genotype data set contained 54519 SNPs for 2905 cows. Statistical analysis A total of 2914 cows with both genotypes and phenotypes were used for GWA analysis. A linear mixed model was used to model the random effects of sampling day and genomics on the logarithm of AMH to estimate the genetic and environmental variance components. The model was as follows: 𝑦𝑖𝑗 = 𝜇 + 𝑑𝑖 + 𝑎𝑗 + 𝑒𝑖𝑗 (1.1) Where yij is the vector of phenotype (AMH), 𝜇 is the overall mean, 𝑑𝑖 is the random effect of the date of sample collection, i= 1,2,…,29, 𝑎𝑗 is the genetic effect of animal j, j=1,2,…,2914, such that 𝒂 = {𝑎𝑗 } ∼ 𝑁(𝟎, 𝐆𝜎𝑎2 ) and 𝐞 is the random error vector such that 𝐞 = {𝑒𝑖𝑗 } ∼ 𝑁(𝟎, 22 Iσ2). Here G=ZZ` is the genomic relationship matrix between animals with Z being the standardized matrix of genotypes and obtained by standardizing the matrix of allelic dosages (M). (VanRaden, 2008) 𝒁= 𝑀𝑖𝑗 − 2𝑝𝑗 √𝑚(2𝑝𝑗 (1 − 𝑝𝑗 ) (1.2) Note that Mij, element ij of M, indicates the number of copies of the reference allele on SNP marker j for animal i whereas 𝑝𝑗 is the allelic frequency of the reference allele, and 𝑚 is the number of markers. The best linear unbiased predictions were calculated by maximizing the log likelihood of the model in E.q 1.1. The accuracy of estimated breeding values was calculated by using following method (Van Vleck, 1993) : 𝑟= 𝜎𝑎2 − 𝑪𝒊𝒊 𝜎𝑎2 (1.3) Here 𝑟 refers to the accuracy of prediction, 𝑪𝒊𝒊 refers to the ith diagonal element of 𝑪𝒂𝒂 which is the prediction error variance-covariance matrix or the portion of the inverse of the mixed model equations that corresponds to animal effects. Breeding values were linearly transformed to estimate the marker effects as explained by (Gualdrón Duarte et al., 2014) ̂ = 𝒁′ 𝑮−𝟏 𝒂 ̂ 𝒈 (1.4) ̂ is the estimate of marker effect, and 𝒂 ̂ is the best Here Z and G have been previously defined, 𝒈 linear unbiased prediction (BLUP) of a. The variances of genetic effects were estimated by the following equations as explained by (Gualdrón Duarte et al., 2014): 23 ̂ ) = 𝒁′𝑮−𝟏 𝒁𝜎𝑎2 − 𝒁′𝑮−𝟏 𝑪𝒂𝒂 𝑮−𝟏 𝒁 𝑉𝑎𝑟(𝒈 (1.5) We divided SNP effect estimates by their corresponding standard errors to obtain test statistics as follows: 𝑆𝑁𝑃𝑗 = 𝑔̂𝑗 √𝑉𝑎𝑟(𝑔̂𝑗 ) (1.6) where the subscript 𝑗 refers to marker j. Here P values were obtained using the z score test as follows: 𝑃 − 𝑣𝑎𝑙𝑢𝑒𝑗 = 2(1 − 𝛷 (|𝑆𝑁𝑃𝑗 |)) (1.7) where 𝛷 denotes the standard normal cumulative distribution function. The false discovery rate (FDR) (Storey and Tibshirani, 2003) of 5% was used as a significance criteria for multiple tests. A linkage disequilibrium (LD) heat map was constructed for significant markers. Number of QTL per peak To determine the number of QTL (quantitative trait loci) per peak we ran GWA analysis again by fixing the top most significant peak (Casiró et al., 2017). The model thus used was as follows 𝑦𝑖𝑗 = 𝜇 + 𝛽𝑝𝑒𝑎𝑘 + 𝑑𝑖 + 𝑎𝑗 + 𝑒𝑖𝑗 (1.8) Here all the terms are as described in Eq. 1.1 except 𝛽𝑝𝑒𝑎𝑘 which is the fixed effect of peak significant SNP. Confidence interval of the QTL peak We used cross validation approach to estimate the 99% confidence interval for the peak significant QTL proposed by Hayes (2013). In this method, we firstly conducted the GWA as 24 described above to get the position of peak significant QTL (p=peak). Then we divided the dataset into two parts to conduct GWA and get the position of the most significant SNP from both datasets and calculate the difference between them (Casiró et al., 2017). We repeated the process 300 times to get the standard error of half the difference between two peaks (h) as follows: 𝑛 1 𝑠𝑒(ℎ̅) = √ ∑(𝑥1𝑖 − 𝑥2𝑖 )2 4𝑛 (1.9) 𝑖 Here 𝑠𝑒(ℎ̅)is the standard error of half the distance between peak significant SNPs of the two split datasets, n is the number of data splits (in this case 300), x1i and x2i are the position of the peak significant SNP of the first and second data set respectively in the ith data split. Assuming symmetric distribution of the peak significant SNP after n splits of data, we calculated the 99% confidence interval of the peak SNP as follows: 𝐶𝐼 = 𝑝 ± 𝑧99.5 𝑠𝑒(𝑥̅ ) (1.10) Proportion of genetic variance explained by the significant region The proportion of genetic variance explained by the significant region was calculated by fitting a model that contains two genetic effects: the genetic effect of the 99% confidence interval of peak significant SNP and the genetic effect of the rest of SNPs. 𝑦𝑖𝑗 = 𝜇 + 𝑑𝑖 + 𝑎𝑝𝑒𝑎𝑘,𝑗 + 𝑎−𝑝𝑒𝑎𝑘,𝑗 + 𝑒𝑖𝑗 (1.11) Here 𝜇 is the overall mean 𝑑𝑖 is the effect of ith date of blood collection, 𝑒𝑖𝑗𝑘 is the residual,𝑎𝑝𝑒𝑎𝑘 and 𝑎−𝑝𝑒𝑎𝑘,𝑗 correspond to genetic effects of the 99% confidence interval of peak significant 25 SNP marker and the genetic effects of the rest of the SNP markers respectively. The proportion of genetic variance can be calculated by: 𝑉𝑎𝑟(𝑎𝑝𝑒𝑎𝑘,𝑗 ) 𝑉𝑎𝑟(𝑎𝑝𝑒𝑎𝑘,𝑗 ) + 𝑉𝑎𝑟(𝑎−𝑝𝑒𝑎𝑘,𝑗 ) (1.12) Where 𝑉𝑎𝑟(𝑎𝑝𝑒𝑎𝑘,𝑗 ) is the estimated variance component associated with the significant genomic region and 𝑉𝑎𝑟(𝑎−𝑝𝑒𝑎𝑘,𝑗 )is the estimated variance component associated with the rest of genome. A likelihood ratio test was used to test the significance of identified region by comparing the likelihood of model in Eq 1.11 to a null model that does not contain 𝑎𝑝𝑒𝑎𝑘 as shown below: 𝑦𝑖𝑗𝑘 = 𝜇 + 𝑑𝑖 + 𝑎𝑝𝑒𝑎𝑘 + 𝑎𝑘 + 𝑒𝑖𝑗𝑘 (1.13) The variance components were estimated by restricted maximum likelihood method using the R package regress (https://cran.r-project.org/web/packages/regress/regress.pdf). GWA analysis was done using gwaR (https://github.com/steibelj/gwaR) package in R. All analysis was done using R version 3.2.0 (http://www.R-project.org/). Identification of candidate genes Firstly, a genomic region on chromosome 11 corresponding to 99% confidence interval of the peak significant SNP was identified as described above. Annotated genes within that region were identified from ENSEMBL genes database v. 88. of the cow genome (v. UMD 3.1) using “GenomicRanges” package in R (Lawrence et al., 2013). 26 RESULTS Heritability Serum concentrations of AMH in the dairy heifers had a phenotypic mean of 438.50 pg/ml and a standard deviation of 604.33 pg/ml. (Figure 1.1) The median AMH concentration was 333.3 pg/ml and it ranged from 2 pg/ml to 14350 pg/ml. The distribution of AMH concentration and log transformed AMH concentrations is also given below which shows an approximate normal distribution. Figure 2.1: Distribution of serum concentration of AMH in dairy Holstein heifers 27 Figure 2.2: Distribution of log transformed serum concentration of AMH in dairy Holstein heifers The variance associated with random day of blood sample collection was 0.015 ± 0.006. The estimated genetic variance associated with AMH was 0.28 ± 0.003 and the residual variance was 0.48 ± 0.020. Finally, the heritability of AMH was 0.36 with a standard error of 0.03. We calculated the accuracy of the breeding values in our study by inverse of the set of linear model equations (the coefficient matrix). The average accuracy of prediction of breeding values in our study using 2905 animals and 54519 markers was 55.7%. The distribution of prediction accuracies is given below in figure 2.3. 28 Figure 2.3: Distribution of accuracy of predicted genomic breeding values of AMH using 2905 animals and 54519 markers GWA Study The genome wide association analysis determined 11 significant SNPs on chromosome 11 and 1 SNP on chromosome 20 (Figure 2.4) based on a 5% false discovery rate (FDR). SNP marker “Hapmap41435-BTA-115556” on chromosome 11 (pos= 95026013 bp) turned out to be the peak significant SNP. 29 Figure 2.4: Manhattan plot of –log10 P values versus genomic location for logarithm of serum concentrations of AMH in dairy Holstein heifers 30 Figure 2.5: Manhattan plot of P values of markers on chromosome 11 for logarithm of serum concentrations of AMH in dairy Holstein heifers Figure 2.6: Manhattan plot of P values of markers on chromosome 20 for logarithm of serum concentrations of AMH in dairy Holstein heifers 31 Table 2.1: Significant associations from genome wide association analysis of logarithm of AMH in dairy Holstein heifers SNP ID Ch r Position (Mbp) P-value q-value Effect BTA-17666-no-rs 11 92.05 1.59x10-6 0.007 - Minor Allele Frequency 0.18 ARS-BFGL-NGS-118517 11 93.546 1.29 x10-6 0.007 + 0.47 Hapmap38572-BTA-115523 11 94.071 5.10 x10-7 0.003 - 0.22 BTA-115525-no-rs 11 94.101 7.77 x10-9 0.0001 - 0.20 BovineHD1100027436 11 94.202 2.00 x10-6 0.008 - 0.22 Hapmap46766-BTA-115526 11 94.446 7.92 x10-7 0.005 - 0.22 Hapmap41435-BTA-115556 11 95.026 5.94 x10-9 0.0001 - 0.18 ARS-BFGL-NGS-12334 11 95.516 4.65 x10-7 0.00386 + 0.37 Hapmap53866-rs29019867 11 95.568 1.40 x10-8 0.00018 - 0.14 Hapmap47514-BTA-115564 11 96.074 7.87 x10-9 0.00013 - 0.16 ARS-BFGL-NGS-114094 11 99.413 2.63 x10-7 0.00279 - 0.10 ARS-BFGL-NGS-110286 20 25.689 1.64 x10-6 0.00794 + 0.46 Number of QTLs When the peak SNP (Hapmap41435-BTA-115556) was fixed in the model, none of the remaining SNP markers reached the level of statistical significance (5% FDR) (Figure 2.7) suggesting that all the significant SNP markers are in LD with a single QTL. 32 Figure 2.7: Manhattan plot after using the peak SNP as a fixed effect We noticed that the only SNP on chr 20 (ARS-BFGL-NGS-110286) which was previously significant (q=0.007) and had a low correlation with the peak, was no longer significant (q=0.085) by fixing the peak SNP (Hapmap41435-BTA-115556). Although the P-value of that SNP did not increase (p=1.56 x10-6-1.65x10-6), it did not reach the level of significance because the new FDR was increased due to the loss of 11 highly significant SNPs on chr 11 having very low (~10-9) P-values. This implies that ARS-BFGL-NGS-110286 on chr 20 is moderately associated with AMH expression. 33 Confidence interval of the peak association on Chromosome 11 The 99% confidence interval of the peak significant SNP ranged from 92879023 bp to 97160473 bp on chromosome 11, a span of roughly 4.28MB. This region contained 68 SNPs and accounted for 7.9% of the genetic variance. When a likelihood ratio test was used to test whether this region accounted for a significant genetic variance, the test was highly significant (p=1.7x10-7). This means that the 99% confidence interval of the peak significant SNP accounted for a significant portion of the genetic variance. Figure 2.8: Manhattan plot of markers on chromosome 11. Markers with in the 99% confidence interval of the most significant SNP are shown in different color. 34 Confidence interval of the peak association on Chromosome 20 The 99% confidence interval of the peak significant marker on chromosome 20 (ARS-BFGLNGS-110286) ranged from 25002762 bp and 26362752 bp, a span of roughly 1.35 MB. This region contained 25 SNPs and accounted for 5.25% of the genetic variance. When a likelihood ratio test was used to test whether this region accounted for a significant genetic variance, the test was significant (p=0.007). This means that the 99% confidence interval of the peak significant SNP on chromosome 20 accounted for a significant portion of the genetic variance. Therefore, the joint variance explained by both the regions simultaneously is 13.25 %. Figure 2.9: Manhattan plot of markers on chromosome 20. Markers with in the 99% confidence interval of the most significant SNP are shown in different color. 35 LD between significant SNPs The LD heat map of all the SNPs with in the 99% confidence interval of the peak significant SNP on chromosome 11 and 20 indicated that there is moderate linkage disequilibrium between most of the SNP markers in that region. However, some SNPs were found to be highly correlated with each other with a LD (r2) value as high as 0.99) The heat map is shown below Figure 2.10: LD of all SNPs (n=68) within 99% confidence interval of peak SNP on chromosome 11arranged in increasing order of base pair position. The significant markers are marked in the map. 36 Figure 2.11: LD of all SNPs (n=25) within 99% confidence interval of peak SNP on chromosome 20 arranged in increasing order of base pair position. The significant marker is marked in the map. Candidate genes The significant regions on chromosome 11 (92879023 bp - 97160473 bp) and 20 (25002762 bp and 26362752 bp) were searched for candidate genes associated with AMH. Gene annotation information was retrieved from Ensembl genes database v. 88. of the cow genome (v. UMD 3.1). The region identified on chromosome 11 contained 81 genes. The most significant SNP was found within gene DENND1A. The region identified on chromosome 20 contained 9 genes. These genes perform a wide range of functions including maintenance of cell structure, cell 37 signaling, cell viability, embryonic development of cardiac, gonadal and brain tissues, embryonic survival, oocyte competence, cancer suppression and immunity. All the candidate genes and their functions have been listed in the appendix DISCUSSION The genomic heritability of AMH has not been reported for any species. Moreover, the genomic heritability of AMH reported in our study (0.36 ±0.03) is the highest for any trait related to reproduction in female cattle. Since endocrine reproductive traits directly reflect a cow’s reproductive physiology and are less likely to be influenced by farm management (Bulman and Lamming, 1978) , Darwash et al., 1999), the heritability of endocrine reproductive traits is expected to be higher (Veerkamp et al., 2000) (Petersson et al., 2007) (Tenghe et al., 2015) relative to direct fertility traits as defined from calving data and insemination records. The moderate to high heritability of AMH along with a potentially positive association of AMH with fertility in cattle indicates that AMH might be helpful in accurate predictions of breeding values for genetic potential of reproduction. The accuracy of genomic predictions depends on a number of factors including size of the reference population, density of markers, effective population size and most importantly the heritability of the trait under selection. We calculated the accuracy of the breeding values in our study by inverse of the set of linear model equations (the coefficient matrix). The average accuracy of prediction of breeding values in our study using 2905 animals and 54519 markers was 55.7%. Interestingly, the mean accuracy matches what would be expected based on a reference population of 3000 animals and a trait heritability of 0.35 (Hayes et al., 2009). 38 A number of genome wide association studies have been conducted in the past on a plethora of reproductive traits in dairy and beef cattle. Most of the GWA studies on fertility traits suffer from inadequate statistical power partly due to low heritabilities (Berry et al., 2014). Nonetheless, a number of QTLs have been identified for fertility traits in cattle (Tenghe et al., 2016) (Pryce et al., 2010) (Höglund et al., 2009) (Berry et al., 2012). However, when it comes to AMH, no GWA study has been reported in any livestock species. Perry et al., (2016) found 3 SNP variants associated with log serum AMH in human males which surprisingly had a sex interaction effect i.e. the same SNPs did not appear significant in females. As data in our study consists of female heifers, there is every possibility that a sex interaction effect exists for serum AMH levels in cattle as well. More research is needed in this regard to do a GWA study on a population that includes bulls and cows. A review of GWA studies in various species revealed that the proportion of genetic variation in complex traits explained by major genes is usually <10% (Visscher et al., 2012). The proportion of genetic variance explained by significant regions mentioned earlier in this study is 13.3%. High density sequencing of the region on Chromosome 11 and 20 might help in identifying the causative QTL. Genes identified from the cow reference genome with in the significant region identified by the 99% confidence interval of the peak significant SNP display a wide range of functions i.e. maintenance of cell structure, cell signaling, cell viability, embryonic development of cardiac, gonadal and brain tissues, embryonic survival, tumor suppression, tumor proliferation, chemo resistance and immunity. Other genes identified in this region belong to olfactory signaling system or micro RNAs. Some of the important candidate genes identified are mentioned below: 39 The most significant SNP (Hapmap41435-BTA-115556 at 95026013 bp on chr 11) for AMH was located within the DENND1A gene (94526960 bp – 95055931 bp). Welt (2012) found that the most significant SNP for polycystic ovary (PCOS) in European and Chinese human females was also found within the same gene. Females suffering from this condition generally have abnormally high AMH concentrations (Pigny et al., 2003). Durlinger (2001) showed that AMH affects sensitivity of follicles to FSH treatments. Since there is a threshold level of FSH required for follicular growth, different follicles might show different thresholds depending the amount of AMH expressed in them. Therefore, AMH may play a role in the determining which follicles undergo selection and which are removed through atresia. The gene NR5A1 gene (95514365-95538847)) encodes SF-1 (Steroidogenic factor 1) protein which binds to two different binding sites at the promoter region of AMH gene (Giuili et al., 1997; Watanabe et al., 2000). SF-1 binding site to AMH promoter is essential for sex and cell specific AMH promoter activity (Giuili et al., 1997) and transcription of key genes involved in sexual development and reproduction. Therefore, our analysis can be validated by previously published research findings. Similarly, the NR6A1 gene which is an oocyte specific transcription repressor also belongs to the same family and plays an important role in embryo development and folliculogenesis. NR6A1 is expressed in unfertilized eggs and preimplantation embryos. In adults, NR6A1 is expressed in the oocytes of primary follicles and all subsequent stages of folliculogenesis. The PTGS1gene (93219287-93245045) has been identified as a candidate gene in a recent GWA study for superovulatory traits (total number of embryos and the number of viable embryos) (Jaton et al., 2015). This study showed that 81% of the significant SNP markers (46/57) for the total number of embryos, were located on Chromosome 11. Jaton et al. (2015) also determined 40 that for the number of viable embryos, 46 out of 47 significant SNPs associated with that trait were located on chromosome 11. All the significant SNP markers on chromosome 11 in that study were located within the region identified in our study (92879023 bp to 97160473 bp on chr 11). The most significant SNP in that analysis (BovineHD1100027188; 93306002 bp) was located nearby the (60,957 bases) prostaglandin-endoperoxide synthase 1 (PTGS1) gene. This gene is responsible for the conversion of arachidonic acid into different form of prostaglandins such as PGE2 and PGF2α (Arosh et al., 2002). Prostaglandins are well known to play an important role in ovulation (Armstrong, 1981) and are routinely used by veterinarians to treat ovarian cysts in dairy. As AMH is identified as an important marker of superovulation response (Monniaux et al., 2010; Souza et al., 2015), these findings suggest that AMH might have a QTL in common with super ovulatory traits. The NADH dehydrogenase (ubiquinone) 1 alpha subcomplex (NDUFA8) (93011815-93029730) transfers electrons with a high redox potential from NADH to ubiquinone. This gene is highly expressed in human heart, skeletal muscle, and fetal heart (Triepels et al., 1998). A meta-analysis of studies in humans indicates that patients with PCOS have a 2-fold higher risk of cardiac disease than normal subjects (de Groot et al., 2011). More recently, AMH has been inversely correlated with the ultrasonographic diameters of the distal and mid-infrarenal aorta and high AMH levels have been associated with the absence of cardiovascular disease in men (Dennis et al., 2013). The Follistatin gene (FST) (25588642-25594057) encodes for Follistatin protein which binds to members of the TGF-β superfamily particularly activin hormone. It was first discovered in the follicular fluid and known to regulate the follicle stimulating hormone (FSH ) secretion from pituitary gland (Ying, 1988). Follistatin and activin interaction is widely known as the 41 autocrine/paracrine regulator of various physiological processes in reproduction including folliculogenesis and maturation of oocytes (Muttukrishna et al., 2004). Furthermore, increased abundance of Follistatin mRNA transcript was found to be positively associated with oocyte competence to fertilize and develop to blastocyst stage (Patel et al., 2007) and bovine early embryogenesis (Lee et al., 2009). Association of AMH with SNP markers adjacent (95027 bp apart) to FST gene indicates there might be a genetic relationship between the two hormones. CONCLUSION We have estimated the genomic heritability of AMH in cattle using an animal effects model based on their genotype information using 60 k standard USDA SNP panel. The higher heritability of AMH (0.36 ± 0.02) compared to other reproductive traits and its positive association with fertility can help accurately predict the breeding values of animal for fertility traits. Therefore, it can possibly be used for genetic improvement of reproductive potential in cattle. We also performed a GWA study to identify the QTL involved in AMH regulation. The study resulted in identification of a ~4.28 MB window on chromosome 11 and 1.35 MB window on chromosome 20 of bovine genome that might contain causative QTL of AMH regulation. We also identified potential candidate genes that appeared to have a key role in AMH expression based on previous research. Some of these genes have been previously reported to be involved in maintenance of cell structure, cell signaling, cell viability, embryonic development of cardiac, gonadal and brain tissues, embryonic survival, oocyte competence, cancer suppression and immunity. This might give us an insight to the mechanisms involved in AMH regulation and endocrine role of AMH in reproduction and development. Furthermore, this same region on Chromosome 11 has been recently identified as being associated with super ovulatory response 42 in an independent population indirectly indicating that some of these candidate genes mediate a role between AMH and super ovulatory response. 43 APPENDIX 44 Table 2.2: List of genes identified with in the significant region on chromosome 11 and 20 ENSEMBLE Gene ID Gene Name Start position End position ENSBTAG00000012827 TTLL11 92737269 92903570 ENSBTAG00000004295 NDUFA8 93011815 93029730 ENSBTAG00000004296 MORN5 93029874 93064357 ENSBTAG00000005525 LHX6 93069014 93090242 ENSBTAG00000016367 RBM18 93101473 93121906 ENSBTAG00000047226 MRRF 93121981 93138808 ENSBTAG00000018426 MRRF 93149379 93158576 ENSBTAG00000006716 PTGS1 93219287 93245045 ENSBTAG00000047610 93268704 93269738 ENSBTAG00000047693 93290982 93291917 ENSBTAG00000046018 93304997 93305947 ENSBTAG00000046137 93313595 93314530 ENSBTAG00000038309 93339271 93340212 ENSBTAG00000038796 93346999 93347931 ENSBTAG00000037739 93401560 93402516 ENSBTAG00000038278 93409030 93409962 ENSBTAG00000039225 93459896 93460798 ENSBTAG00000038726 93563425 93564411 ENSBTAG00000037542 93584334 93585269 ENSBTAG00000000726 OR1J1 93593230 93594171 45 Table 2.2 (cont’d) ENSBTAG00000046126 OR1J2 93609988 93610929 ENSBTAG00000040047 93617052 93618040 ENSBTAG00000037767 OR1N1 93638723 93639658 ENSBTAG00000047728 93646064 93647008 ENSBTAG00000047112 93655028 93655969 ENSBTAG00000046536 93670180 93671118 ENSBTAG00000045527 93678033 93678974 ENSBTAG00000045545 93691882 93692865 ENSBTAG00000020660 93702914 93703858 ENSBTAG00000038551 OR1N2 93731042 93731977 ENSBTAG00000046221 OR1Q1 93742434 93743378 ENSBTAG00000045528 93765538 93766494 ENSBTAG00000001549 OR1L1 93797496 93798488 ENSBTAG00000048218 OR1L3 93808260 93809237 ENSBTAG00000038822 93835432 93836470 ENSBTAG00000038941 93853095 93854133 ENSBTAG00000037822 93866953 93868392 ENSBTAG00000038665 93885139 93886080 ENSBTAG00000004667 93900519 93901442 ENSBTAG00000030678 93927186 93927978 ENSBTAG00000030677 93935690 93936631 ENSBTAG00000038249 OR5C1 93960722 93961672 46 Table 2.2 (cont’d) ENSBTAG00000030676 OR1K1 93969256 93970206 ENSBTAG00000030675 PDCL 93984123 93991685 ENSBTAG00000023867 RC3H2 94010161 94058169 ENSBTAG00000042329 SNORD90 94037106 94037216 ENSBTAG00000039815 ZBTB6 94072877 94074965 ENSBTAG00000038610 ZBTB26 94081312 94082670 ENSBTAG00000039172 RABGAP1 94103009 94264248 ENSBTAG00000040296 GPR21 94188119 94190302 ENSBTAG00000024604 94221939 94319233 ENSBTAG00000021921 STRBP 94281217 94418835 ENSBTAG00000042085 U6 94384741 94384847 ENSBTAG00000014391 CRB2 94501988 94523379 ENSBTAG00000003610 DENND1A 94526960 95055931 ENSBTAG00000044885 SNORA25 94574530 94574657 ENSBTAG00000023860 94931694 94932632 ENSBTAG00000010990 LHX2 95125308 95145048 ENSBTAG00000019470 NEK6 95314593 95400813 ENSBTAG00000003067 PSMB7 95401692 95458914 ENSBTAG00000017576 ADGRD2 95484105 95508348 ENSBTAG00000009017 NR5A1 95514365 95538847 ENSBTAG00000040585 NR6A1 95551663 95586813 ENSBTAG00000029841 bta-mir-181a-2 95709411 95709520 47 Table 2.2 (cont’d) ENSBTAG00000029896 bta-mir-181b-2 95710626 95710714 ENSBTAG00000004848 OLFML2A 95780659 95805530 ENSBTAG00000044811 U6 95816939 95817043 ENSBTAG00000039223 WDR38 95846030 95850595 ENSBTAG00000003205 RPL35 95850116 95854734 ENSBTAG00000015278 ARPC5L 95859894 95867086 ENSBTAG00000015286 GOLGA1 95869270 95911957 ENSBTAG00000015553 SCAI 95925113 95996116 ENSBTAG00000045071 SNORA64 95982801 95982910 ENSBTAG00000008033 PPP6C 96044189 96085315 ENSBTAG00000015098 RABEPK 96092486 96113995 ENSBTAG00000007662 GRP78 96115572 96119306 ENSBTAG00000011544 GAPVD1 96144147 96208779 ENSBTAG00000043246 U6 96242761 96242864 ENSBTAG00000048297 U5 96264484 96264596 ENSBTAG00000010271 MAPKAP1 96278654 96511560 ENSBTAG00000013314 PBX3 96719400 96772227 ENSBTAG00000019834 ARL15 24955390 25026808 ENSBTAG00000003728 NDUFS4 25407689 25523382 ENSBTAG00000003329 FST 25588642 25594057 ENSBTAG00000046997 NA 25631428 25632999 ENSBTAG00000005380 MOCS2 25965175 25975522 48 Table 2.2 (cont’d) ENSBTAG00000019289 ITGA2 25984555 26089593 ENSBTAG00000016525 ITGA1 26116747 26227530 ENSBTAG00000046575 NA 26174067 26174830 ENSBTAG00000003268 PELO 26278617 26280571 49 LITERATURE CITED 50 LITERATURE CITED Armstrong, D.T. 1981. 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Rev. 9:267–293. doi:10.1210/edrv-9-2-267. 59 CHAPTER THREE 60 Relationship of Anti Mµllerian Hormone with Reproductive Traits in Holstein Heifers ABSTRACT AMH is an endocrine marker of reproductive potential in various species of animals. Superovulation response and some traits of reproductive performance in dairy cows like conception rate and herd longevity are positively correlated with AMH concentration. The objective of this study was to look at the relationship of dairy heifer fertility with AMH concentrations using 3071 Holstein dairy heifers. Measures of reproductive performance analyzed were: first service conception rate of animals subjected to artificial insemination via regular or sexed semen, conception rate following embryo transfer, overall probability of conception, probability of abortion, number of services per conception, age at first calving and number of days open at first lactation. Results indicated that the probability of conception has a moderately significant (P=0.03) linear association with AMH concentration in animals within the first quartile of AMH, suggesting a possible threshold effect of AMH. However, no phenotypic relationship was found between AMH and the other measures of reproductive performance in heifers. Future studies will evaluate whether AMH concentration is correlated with measures of reproductive performance in later stages of productive life when animals are more prone to reproductive problems. 61 INTRODUCTION Efficiency of reproduction is one of the primary determinants of dairy farm profitability. Reproductive losses on a dairy farm translate into a number of short term and long term economic losses such as longer calving intervals, shorter herd life, higher replacement costs, higher costs of veterinary treatment and drugs, etc. Total losses due to reproductive failure equals about 2% of the gross production value or 10% of an average farmer's income (Dijkhuizen et al., 1984). Therefore, in addition to optimizing reproductive management of animals on the farm, identification and selection of animals with higher genetic potential for reproduction and successful application of assisted reproductive technologies (ART) are equally important to maximize fertility. However, the rate of genetic gain depends on the heritability of reproductive traits while the success of ART depends on successful identification of animals with superior genetic potential for super ovulatory traits. AMH is a novel endocrine indicator of reproductive potential in animals. We have established AMH concentration in Holstein heifers (n = 2905) is highly heritable compared with other reproductive traits (h=0.36±0.02). AMH has already been reported to be positively associated with antral follicle count (AFC) (Ireland et al., 2008; Rico et al., 2009; Batista et al., 2014), superovulation response (Monniaux et al., 2010; Souza et al., 2015), in-vitro embryo production (IVEP) (Guerreiro et al., 2014; Gamarra et al., 2015; Vernunft et al., 2015), dairy herd longevity (Jimenez-Krassel et al., 2015), maintenance of pregnancy, and pregnancy rate in cows bred on estrus (Ribeiro et al., 2014). Moreover, AFC which is highly positively correlated with AMH concentration, is also positively correlated with number of morphologically healthy oocytes, progesterone and testosterone production during estrous cycles, responsiveness of granulosa and thecal cells to gonadotropins in vitro and responsiveness to superovulation. Taken together, 62 circulating AMH concentration has the potential to be a unique phenotypic marker that may be useful to genetically improve reproduction in dairy cattle. The present study used a large number of Holstein heifers (n = 3259) to test the hypothesis that AMH concentration is positively correlated with fertility. To test this hypothesis, we examined the association of AMH concentration with the following reproductive traits: • Probability of conception to first service • Probability of conception in embryo recipients • Probability of conception after multiple services • Number of services per conception • Probability of abortion • Days open in first lactation animals • Age at first calving • Differences in AMH concentrations between pregnant and non-pregnant animals MATERIALS AND METHODS All experiments involving cattle were approved by the IACUC at Michigan State University. Adult Holstein heifers (n = 3259, 11-15 months old, located on Green Meadow Farms Inc, Elsie, MI) were subjected once to two intramuscular injections of PGF2α spaced 11 d apart to synchronize estrous cycles. Heifers were synchronized in groups of 95 to 124 heifers once or twice per month for a total number of 29 groups. At 96 h after the last PGF2α injection, a single tail vein blood sample was taken from each heifer to measure serum AMH concentration and establish relative size of the ovarian reserve. Blood samples were taken beginning on 4/18/2014 and ending on 12/4/2015. Follicle hair samples were collected at this times for 63 genotypic analyses. Animals that were considered freemartins (n=144) and animals that were sold as replacements to other farmers (n=243) were not included in statistical analyses of reproductive performance as lactating animals. After completion of the PGF2α -induced estrous cycle, heifers were subjected to artificial insemination (AI) at the next detected “standing” estrus or the next morning after standing estrus, and palpation of uterine contents 45 to 60 days after AI was used to diagnose pregnancy. Heifers not diagnosed pregnant after AI were subjected to AI, as just explained (except PGF2α was not used), up to 5 to 6 times. After calving, and starting at 45 DIM, cows were subjected to AI at standing estrus after either of two injections of PGF2α or at fixed-time AI (using Ovsynch technology) at discretion of farm personnel and pregnancy determined 35 d after AI (via palpation or ultrasonography). Cows exhibiting estrous behavior before pregnancy diagnosis were inseminated at standing estrus while cows diagnosed not pregnant were given a single PGF2α injection if a corpus luteum was present and inseminated at the next standing estrus. Cows without CL were given two PGF2α injections spaced 11 d apart as explained for heifers. This breeding regimen in cows continued up to 4 to 5 times. Records on reproductive performance, level of milk production, health, and reasons for culling of each individual animal at Green Meadow Farms were maintained in an on-the-farm computer using the commercial DairyCOMP 305 software program. Relevant information for each cow was recorded daily into DairyCOMP 305 by Green Meadow Farms’ managers and selected employees. Statistical analysis Logistic regression was used with each model including a linear coefficient on serum concentration of AMH to assess the effect of AMH on first service conception rate of animals subjected to AI via regular or sexed semen, conception rate in embryo recipients, overall 64 conception rate and abortion rate. The same phenotypes were also examined by using AMH quartiles as a factor with four levels followed by using nesting linear coefficients on AMH within each quartile separately. This was pursued to allow for the possibility of threshold effects; i.e., a linear relationship with AMH may only exist before or beyond a certain quartile. Quartile means were separated using the Tukey test. The cutoff values for AMH quartiles are given below: Table 3.1: Cut off values of quartiles for AMH concentration Cut off values Quartile 1 (pg/ml) <198.96 Quartile 2 (pg/ml) >198.96 and <323.17 Quartile 3 (pg/ml) >323.17 and <502.88 Quartile 4 (pg/ml) >502.88 Furthermore, we examined differences in AMH concentrations for binary traits i.e. pregnant vs non-pregnant on first service for each of regular semen, sexed semen and embryo transfer recipients, pregnant vs non-pregnant for all animals that were bred at least once, and aborted vs non-aborted animals using a one-way ANOVA with AMH concentration as a dependent variable. A Poisson regression model was used to study the effect of AMH concentration on the number of services per conception. In a similar manner with the other traits, we also used AMH quartiles and with separate linear coefficients on AMH within each quartile in separate analysis to model the number of services per conception. A simple linear regression model was also used to study the effect of AMH on age at first calving and days open in the first lactation. 65 All analyses were done using the ‘glm’ function for Poisson and logistic regression and the ‘lm’ function for linear regression in R programming software version 3.3.1. RESULTS Probability of conception in embryo recipients No overall relationship (P>0.3) between linear AMH concentration and probability of conception was determined for embryo recipients using a classical logistic regression analysis. There was a marginally significant relationship (P=0.03) between probability of conception in embryo recipients and their AMH concentration with in the first quartile. However, no such relationship was found for animals within the 2nd, 3rd and 4th quartiles. There was no significant difference in conception rates between the quartiles separated using the Tukey test. Least squares mean AMH concentration of animals that were successfully pregnant (336.97±11.76) on embryo transfer were not significantly different from animals that failed to become pregnant (314.19±12.57). Probability of conception to first service in artificial insemination recipients No relationship was found between linear AMH concentration and probability of conception in AI recipients using regular semen (P>0.9) and sexed semen (P>0.7). There was no significant difference of probability of conception for regular and sexed semen recipients between the quartiles separated using Tukey HSD.Least squares mean AMH concentration of animals that were successfully pregnant to first service using regular AI semen was 293.67±9.38verses 298.74±10.08for non-pregnant animals respectively. Least squares mean AMH concentration of animals that were successfully pregnant to first service using sexed semen was 309.55±14.05verses 305.40±13.43for non-pregnant animals respectively. 66 Table 3.2: Least square geometric mean AMH concentrations for different reproductive events Event Yes No P-value Conception to Embryo transfer 336.97±11.76 314.19±12.57 0.21 Conception on first AI (regular semen) 293.67±9.38 298.74±10.08 0.71 Conception on first AI (sexed semen) 309.55±14.05 305.40±13.43 0.83 Conceived at least once 307.74±4.83 293.07±24.25 0.56 Abortion 307.54±21.76 307.68±4.95 0.99 Table 3.3: Relationship of AMH with probability of conception nested within quartiles Event Logistic regression P-values Conception to Embryo transfer Conception on first AI (regular semen) Conception on first AI (sexed semen) Quartile 1 0.03 n=221 0.06 n=378 0.85 n=169 Quartile 2 0.13 n=226 0.757 n=378 0.89 n=164 Quartile 3 0.10 n=221 0.203 N=391 0.84 n=155 Quartile 4 0.30 n=256 0.89 n=343 0.69 n=169 Overall probability of conception No relationship (P>0.4) was found between probability of conception and linked linear function of AMH concentration. 2964 animals were pregnant out of 3072 animals that were bred at least once. Least squares mean AMH concentration in animals that conceived (307.74±4.83) verses those who never conceived (293.07±24.25) were not different from each other. Probability of abortion No relationship (P>0.5) was found between probability of abortion and linked linear function of AMH concentration. 146 animals aborted out of 2964 that were confirmed pregnant. Least 67 squares mean AMH concentration in aborted (307.54±21.76) verses non aborted (307.68±4.95) were not different from each other. Days open Number of days open after first lactation had a near-zero correlation with AMH (r=-0.02) such that there was no statistically significant relationship (P>0.39) between them. Figure 3.1: Plot of number of days open after first lactation and serum AMH concentration Age at first calving Age at first calving had a near-zero correlation with AMH (r=-0.004) such that there was no statistically significant relationship (p>0.8) between the age at first calving and AMH concentration. 68 P>0.8 r= -0.004 Figure 3.2: Plot of age at first calving and serum AMH concentration Number of services per conception Number of services per conception had a low negative correlation (r=0.019) with AMH which was not statistically significant (P> 0.2) when analyzed using Poisson regression model assuming quasi-Poisson distribution. When the AMH covariate was divided into quartiles, there was no difference in number of services per conception between the quartiles. 69 DISCUSSION Correlation between AMH with fertility traits has been studied in a number of different ways. Redhead et al., (2017) placed animals into LOW, MEDIUM and HIGH AMH groups, respectively. Jimenez-Krassel et al., (2015) divided the animals into quartiles based on AMH concentrations as 11 to 12 months old heifers and examined differences in fertility traits between quartiles. They concluded that the herd longevity was higher for second and third quartile than the first and fourth quartile suggesting a quadratic relationship. Therefore, we adopted a set of different strategies: first looking at overall linked linear relationships of fertility traits with AMH, followed by linear coefficients on AMH within each quartile and between quartile comparisons. Our results indicate that AMH appears to be moderately associated with probability of conception in embryo recipients within the first quartile. However, no such relationship appears to exist for animals in the other AMH quartiles, suggesting that there might be a threshold level of AMH concentration required for successful pregnancy. That is, once this threshold is achieved, higher AMH concentrations are not associated with higher probability of conception. Lahoz et al., (2012) reported a similar observation in Rasa Aragonesa sheep, and suggested the cut off value of 97 pg/ml to distinguish between females with low and high fertility. We found no evidence of a relationship between AMH and probability of conception to first service for heifers subjected to timed AI using sexed or regular semen and embryo recipients. Ribeiro (2014) presented similar results that no relationship existed between AMH and pregnancy for cows bred on timed AI protocol. However, cows with low AMH concentration had lower pregnancy rates after first service for cows bred after detection of estrus. This is probably due to the fact that estrus synchronization procedure might have optimized the follicle 70 development and ovulation process such that variation in AMH concentrations was no longer associated with pregnancy. We determined no evidence that overall probability of conception of heifers subjected to multiple fixed time AI, and probability of abortion in heifers was associated with AMH. Furthermore, no relationship was found between AMH with days open, number of services per conception, age at first calving and probability of abortion in heifers. Jimenez-Krassel (2015) showed similar results with a much smaller dataset. Age at first AI, at first conception, and at each calving did not differ among the different AMH quartiles. This can possibly be explained by considering the fact that AMH is correlated with the number of follicles but not the quality of oocytes. Heifers being mono ovulatory animals, need only a single oocyte per successful pregnancy. Therefore, their probability of conception may be independent of the number of follicles in the ovary. In contrast to heifers, dairy cows of mixed ages (up to 8 parities) with a low AFC, which is correlated positively with AMH , had a significantly lower conception rate to first AI, required a greater number of AI to conceive, and had a greater calving interval compared with cows with an intermediate or higher AFC (Mossa et al., 2012). Cows with low AFC and AMH have abnormal changes in endometrial thickness during the estrous cycle (Jimenez-Krassel et al., 2009), which suggest that the endometria of such cows are less capable of conceptus implantation and maintenance of pregnancy. Moreover, cows with low AFC also have a lower concentration of progesterone (Jimenez-Krassel et al., 2015) which is required to play an important role in maintenance of pregnancy. Ribeiro (2014) showed that lactating cows with low AMH had greater risk of pregnancy loss than cows with intermediate or high AMH. Perhaps, compared with heifers, fertility in cows with low compared with higher AMH is more sensitive 71 to the physiological stress related to lactation and decreased progesterone concentration (Sartori et al., 2002). Therefore, heifers may not be the ideal model to study the effect of AMH on fertility. CONCLUSION In summary, AMH concentration shows some tendency to predict the probability of conception in embryo recipient heifers within the first quartile of AMH. Hence, there may be a threshold level of AMH required for optimum probability of conception in embryo recipients as the relationship only exists in the first quartile animals. However, other reproductive parameters in heifers such as age at first calving, days open, conception rates, and probability of abortion are not related with serum AMH concentrations. 72 OVERALL CONCLUSIONS AND FUTURE DIRECTIONS Anti Mullerian hormone (AMH) is considered to be an endocrine marker of fertility and super ovulatory response traits in cattle. We set out to estimate the genomic heritability of AMH in Holstein heifers based on their genotype information using 60 k standard USDA SNP panel. The heritability of AMH (0.36 ± 0.02) that we estimated is relatively large compared to conventional but economically relevant reproductive traits. Furthermore, its well documented association with super ovulatory response hints at the possible use of AMH for animals that respond better to superovulation. We also performed a GWA study to identify the QTL involved in AMH regulation. The study resulted in identification of a ~4.28 MB window on chromosome 11 and a 1.35 MB window on chromosome 20. These regions likely contain a causative QTL for AMH regulation given that we also identified potential candidate genes in those regions that appeared to have a key role in AMH expression based on previous research. Some of these genes have been previously reported to be involved in maintenance of cell structure, cell signaling, cell viability, embryonic development of cardiac, gonadal and brain tissues, embryonic survival, oocyte competence, cancer suppression and immunity. We also looked at the correlations of AMH with reproductive traits in heifers. AMH concentration shows some tendency (P=0.03) to predict the probability of conception in embryo recipient heifers. There might be a threshold level of AMH required for optimum probability of conception in embryo recipients as the relationship only exists in animals having low AMH. Other reproductive parameters in heifers and first lactation cows like age at first calving, days open, probability of conception, probability of abortion, and number of services per conception did not appear to be related with serum AMH concentrations. However, it seems that these associations should be studied in later parities as these heifers continue to mature. 73 Further research needs to be done on the candidate genes identified in this study. Some of these genes have been studied extensively in the past. For example NR5A1 knock out mice showed complete adrenal and gonadal agenesis (Luo et al., 1994), and mutations in this gene caused ovarian insufficiency. (Lourenço et al., 2009). However, validation of other genes should be done by a series of experiments. Firstly, fine sequencing should be done in the significant genomic region to detect the causative QTL. 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