"Timely pregnancies are essential to reproductive success on dairy farms. The primary objective of this thesis was to demonstrate the relationship between previous calving interval and body condition change during the 1st 30 days in milk (DIM) and their relationship to subsequent fertility and health. Cows that became pregnant before 130 DIM had a greater chance of maintaining or gaining body condition during the 1st 30 d of the subsequent lactation. Cows that maintained or gained body condition during the 1st 30 DIM had a greater chance of pregnancy at 1st AI and reduced chance of pregnancy loss 35 to 60 d post-AI. This improved chances of becoming pregnant by 130 DIM again. We refer to this relationship as the 'high fertility cycle'. Cows that lost less body condition during the 1st 30 DIM also experienced fewer periparturient disorders. In order to maximize chances for pregnancy by 130 DIM it is critical to detect non-pregnant cows as early as possible and utilize a timely resynchronization program for re-insemination. The second objective of this thesis was to develop an early and highly accurate method to diagnose non-pregnancy. We utilized two within cow samples of PSPB taken before and after the time of embryonic attachment to diagnose non-pregnancy with 100% accuracy at 24 d post-AI. The third objective of this thesis was to use this early non-pregnancy diagnosis method and a short resynchronization protocol in an attempt to create timely pregnancies. We utilized CIDRs to prevent spontaneous ovulation and synchronize cows for re-insemination at 35 d post-AI. The control group was re-inseminated 42 d post-AI. The cows re-inseminated by 42 d post-AI had greater PR/AI and a greater percentage pregnant by 130 DIM."--Page ii.
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