THE EFFECTS OF VARIED LIGHTING REGRMES 0N REPRODUCTION IN MENK (MUSTELA VESON) Thesis for the Degree of M. S. MECHIGAN STATE UNWERSITY Larry C. Holcomb" ‘1 9 62 _.___....—-——-——"'"“"’—'_ L I B R A R Y Michigan State University THE EFFECTS OF VARIflD LIGHTING REGIZ-{ES or: REPRODUCTION 11‘? 3.1:}; (Mustela vison) by Larry C. Holcomb AN ABSTRACT OF A THESIS Submitted to Michigan State University in partial fulfillment of the requirements - for the degree of MASTER OF SCIENCE Department of Zoology 1962 @me ABSTRACT THE EFFECTS OF VARIED LIGQTIXG REGIHES ON REPRODUCTIOX IN KIIK (Mustela vigon) by Larry C. Holcomb The effects of varied lighting regimes on the reproduc- tion of pen-raised mink (Mustela xison) were investigated by two emperimental studies during the breeding season of 1961. EXperiment I was conducted at the EXperimental Fur Animal Station of the Department of Poultry Science on the campus of Michigan State University; EXperiment II was carried out at the Dyer Mink Ranch, a commercial Operation in Ingham county, Michigan. ‘ In EXperiment I, two color phases of mink, sapphire and dark, were individually confined in standard outdoor pens some of which were e uipped with electric lights to provide for the occupants illumination after sunset. The mink were divided into groups consisting of 10 dark and 10 sapphire females illuminated before mating, 10 dark and 10 sapphire females illuminated before and afte mating, 11 dark and 10 sapphire females illuminated after mating, and 85 control animals consisting of 15 dark males and 10 sapphire males plus 25 sapphire females and 35 dark females. Ten dark and ten sapphire males were illuminated before and after mating. The illuminated groups received daily 82 minutes of extra "daylight" by electric lights after normal sunset. The 2 females and males used as a control, received only the light normally available to out-door cages. In EXperiment II, color phases of sapphire and pastel were confined individually in pens housed in a shed. The animals were divided into two groups consisting of 16 pastel females and 21 sapphire females illuminated after mating plus 20 pastel and H2 sapphire females receiving no addi- tional illumination. The females illuminated were eXposed daily to 62 minutes of extra illumination from electric light after sunset. Control females were eXposed only to the light normally available in the roofed shed. Males employed'in matings received only normal light. Males were already sexually active before EXperiment I was started on February 1st. No significant differences were noted in the behavior of illuminated males. Vaginal smears proved that female mink were brought into estrus earlier than normal after increased illumination be- fore c0pulation. Females subjected to increased illumination beginning on February 1st were receptive to males beginning- on February 15. This was 18 days ahead of the control group which were not willing to mate until March 5th although mat- ings were tried daily beginning February 15th. Females illuminated after mating had a shorter average gestation period and/or had an average of more kits per lit— ter than the control groups. Females illuminated only before mating had much longer average gestation periods than those illuminated both prior to and following mating. Much of the data was significantly different at the .05 level. Studies of the control group showed clearly a tendency for shorter gestations in the late-mated females and longer gestations in the early-mated females. Testes and ovaries from sacrificed animals in EXperiment I and‘from casualty mink at a commercial ranch showed pro- gressive growth of these organs at the onset of breeding. No significant difference was noted in the gonad size of il- luminated mink sacrificed and control animals. The reproductive cycle in the sapphire mink seemed more effected by the increased illumination than those of the dark and pastel mink. THE EFFECTS OF VARIED LIGHTING REGIMES ON REPRODUCTION IN MINK (Mustela vison) by Larry C. Holcomb A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Zoology 1962 ii ACKNOWLEDGEMENTS I would like to eXpress my gratitude to both the depart- ments of Poultry Science and Zoology at Michigan State Univer- sity for generous help and assistance with this project. Special thanks go to professors Philip Schaible and Robert Ringer of the former department and to professors Rollin‘H. Baker and Philip Clark of the latter department for their advice and guidance. Also, I would like to thank Mrs. Marjorie Tetzlaff for preparing slides of smears and gonad materials, and Richard Aulerich and Gordon Shelts for their valuable assistance at the EXperimental Fur Animal Station. Mr. James Dyer deserves much credit for the results of EXperment II carried out at his commercial mink ranch. Finally, I am indebted to the King Mink Ranch for reproduc- tive organs sent us in January. This project was accomplished while I held a National Defense Graduate Fellowship grant in Zoology made available by the United States Department of Health, Education, and Welfare. CONTENTS ACKNOWLEDGEMENTS .............L................... LIST OF PLATES AND FIGURES ....................... LITERATURE‘REVIEW ................................ INTRODUCTION ..................................... Delayed implantation ‘ Steady increase of normal light PROCEDURE ........................................ Lighting technique Selection of animals and grouping Preparation of vaginal smears Readiness of mating Statistical evaluation RESULTS ......................................... Vaginal smears Gonad deveIOpment Readiness to mate DISCUSSION ....................................... Comparison of (LL) and (LN) females Comparison of (NL) and (NN) females Comparison of results in 1959 sm’fl‘iimY 00.00....0.0...O..0...OOOOOOOOOOOOOOOOOOOO LITERATURE CIT}:D 0.00....0....OOOOOOOOOOOOOOOOOOOO. Page ii iv iii PLATES I. TABLES I. II. III. IV. V. FIGURES I. II. III. LIST OF PLATES, TABLES AND FIGURES Cells in vaginal smears of mink at different stages during the repro- dUCtion CYCle {0.00.0000coo-000000000000. Female mink mated in each eXperiment .... Effect of illumination on mating and whelping ............................ Effect of light on sapphires (EXp. I) ... Effect of light on darks (EXp. I) ....... Effects of light on mink (Enp. II) ...... Rate of increase of light per week ...... Comparison of date mated and length of gestation period (EXp. II) ........... Comparison of date mated and length Of geStation pePIOd (Exp. I) 000000000000 Pag 17 11+ 22 23 25 33 3% iv LITERATURE_REVIEW Considerable research has been conducted on the effects of various lighting regimes on animal reproduction. Kirkpatrick and LeOpoldl(1952) demonstrated that a daily quota of 10 hours of light, including a one-hour interruption of light at night, causes gonadal activity in bobwhite quail, (Cglinus vigginianus). Bissonnette (1935) found that when light was decreased from 17 hours to 6 hours per day that the ferret (Mustela putorious) went into anestrus from estrus. Estrus was again resumed when light was increased. He also found that ferrets came into estrus sooner on 1% hours than on 2h hours of light daily. This indicated a need for both light and dark intervals. Bissonnette and Bailey (1936) by increasing the daily hours of light induced three ferrets to come into estrus --- one eachfin November, December, and January. Two of them actually bred. Hammond (1951) reported that when mink were subjected to a constant 7-hour light period followed by a constant 5- hour dark period in winter and then returned to natural light at the end of February, the gonads of both females and males were as small in mid-March (the usual mating season) as in mid-sunmer. He also found that when ferrets were placed on a constant 1H-hour or 24-hour light day, those on the former light period came into estrus sooner than those on the latter light period, thus stressing again the need for light-dark intervals. Pearson and Enders (19hh) subjected female mink to 1.5 hours of added illumination after sunset: (1) prior to‘and following mating, and (2) after mating. A control group not illuminated had a mean gestation of 5%.? days. Ten females, illuminated before and after mating, had a mean gestation of h9.h days. Nineteen females, illuminated after mating, had a mean gestatign of 50.5 days. When these authors subjected seven females to a shorter photOperiod (1.5 hours less than normal), their gestation periods were not appreciably length- ened from animals receiving only normal light. HronOpulo (1956) conducted lighting eXperiments in Russia. Three groups of ten female mink each were subjected to: (1) 15 hours of light per day from mating to whelping (more than the normal amount), (2) seven hours of light per day from mating to whelping (less than the normal amount), and (3) natural daylight conditions. The first group whelped an average of 5.9 kits per female whereas those on a natural light day averaged 5.1 young per female. The females on a 7 hour day had an average of only H.6 kits per litter. Pearson and Enders (19hh) shortened the gestation period in the marten (Martgg amerigana) by steadily increasing the length of the day by artifical light beginning in September. They had been successful in mating three of eight females under increasing artificial light conditions. This was a high percentage when compared with previous eXperience with captive marten. They believed that an increase in the length of daylight shortened the implantation period and reduced loss of blastocysts in some females. Hansson (19%?) found that increase in the size of mink ovaries and cornua uteri were coincident with the lengthening of periods of illumination and that the length of gestation was decreased with increased illumination. INTRODUCTION The basic objective of the eXperiments to be described was to study the effect of various lighting regimes on the reproduction of pen-raised mink (Mustela ziggn) so as to acquire information that might aid mink renchers to Obtain maximum production from their herds. Comparisons were to be made between illuminated and control animals on the basis of; 1) comparison of vaginal smears in females, 2) size of the reproductive systems in males and females, 3) readiness of males and females to mate, M) length of the gestation period, 5) number of kits per litter, and 6) weight of kits at birth. The relationship between the number of hours of light and the hours of dark per day controls the timing of repro- ductive processes in many animals. The perception of this daily relationship in mink and other mustelids is through the eyes and the Optic nerve and is ultimately received by the anterior pituitary gland which regulates gonadal activity (Pearson and Enders, 19hh; Bissonnette, 1935). In mink, and in some other members of the Mustelidae, when the egg is released by the Ovary and fertilized, it does not implant in the uterine wall until a varied amount of time has elapsed. In the marten.(Ma;§2g,gmgrigan§) blastocysts are not implanted for a period of several months. In no other family of mammals does the gestation period vary as much as it does in the Mustelidae. The period in mink according to Hansson (19h?) varies generally between 39 and 76 days with the average close to #9 days for once-mated females. The long gestation period in some female mink seems to be due to delayed implantation of the blastocyst. It has been determined that blastocysts may not be implanted for as many as 16 days (Hansson, 19%?) or 20 days (Pearson and Enders, 19MH) after conception. However, Pearson and Enders (19h4) noted that gestation periods are shortest when the females conceive late in the breeding season. Also, theSe authors determined that the shorter the gestation period the larger the number of offSpring produced. This variability in the number of offSpring suggests that some blastocysts are never implanted, since Hansson (19%7) found that females re- leased an average of 8.73 i .30 ova but produced only an average of h.37 :_.005 young. This variation may have a logical eXplanation. Pearson and Enders (19hh) hypothesized that the increasing length of days in early Spring induces the liberation of follicle- stimulating hormones (FSH) from the anterior pituitary gland, resulting in growth of ovarian follicles and indirectly the preparation of the uterus for implantation. COpulation stimulates secretion of luteinizing hormone (LH) from the pituitary causing mature follicles to ovulate. If COpulation occurs early in the breeding season, the FSH secretion at ' this time from the pituitary is not great enough to raise the estrogen level to a height necessary to prepare the uterus for implantation. These changes probably do not take place until longer days stimulate release of more FSH. Consequently, the implantation of the fertilized egg is delayed. Mink mated late in the breeding season have already obtained suf- ficient estrogen to prepare the uterus for rapid implantation. The changes in the photOperiod to which animals are sub- jected are gradual and continous. For regions outside the trOpics, there is a gradual increase in the number of hours of light per day for six months of the year. There is then a gradual decrease in the number of hours of light per day for the other six months of the year. These changes become greater the further one proceeds away from the Equator. The annual regularity of these light cycles is striking. This constancy is far from the case with regard to other environ- mental factors such as temperature, humidity, air movements, and rainfall. It would not be surprising then, that in the course of evolution, the daily.light changes, eSpecially in temperate and frigid zones have been adapted to by animals to insure that the young are born at the most suitable season of the year for survival and develOpment. So far, it has not been determined whether it is merely the increasing length of the days that effect the mink re- productively or whether it is the constant rate of increase of light per day ranging from early February to early May. There is an increase of from h to 19 minutes of light per week from the 6th of January to the 12th of February. From then until May 6 there is a weekly increase of not less than 19. or more than 22 minutes of light. The ranges of increase and decrease in light on both ends of this interval change 7 much faster. An axample is the range of from H to 19 minutes increase of light per week between January 1 and February 6 and an increase per week of 18 to 3 minutes between May 6 and June 2%. (Fig. I). . There are 713 minutes between sunrise and sunset on March 15th and 795 minutes on April 15th -- a difference of 82 minutes. Between February 15th and March 15th and between April 15th and May 15th there are also differences of about 82 extra'minutes of daylight, reSpectively. (Fig. I) Earlier, Hansson (19h?) determined that there was a maximum of stimu- lation to the mink's reproductive tract from the effects of light when there was about 90 extra minutes of illumination per day. _ Mink generally mate from early harch to early April. This season varies with latitude. 'Mink farmers in Michigan plan to begin their breeding program between the 5th and 10th of March. If March light conditions could be produced in February, the breeding season for the mink might be induced to start at an earlier date. Hawmond (1951) reperted finding Sperm in male mink late in December. The object of the experiment was to determine the reproductive capacity of both males and females during February. It was desirable then to com- pare the mating behavior of illuminated and control mink. Would increased light stimulate gonad growth in both sexes and hasten the breeding season in mink? Could female mink be brought into estrous faster with increaSed illumination? ._ >m<=z