OPTIMIZING REPRODUCTIVE EFFICIENCY IN PREVIOUSLY INSEMINATED LACTATING DAIRY COWS AND PHYSIOLOGICAL RESPONSE TO INTRAVAGINAL DELIVERY OF GNRH AND PGF2[alpha]

Abstract

The objectives of the experiments presented in Section I were: (1) to determine embryo mortality (EM) around the period of maternal recognition of pregnancy and identify ovarian dynamics alterations in cows that suffered EM, and (2) evaluate resynchronization programs based on ovarian structures present at nonpregnancy diagnosis (NPD) for lactating dairy cows. Objectives of the experiments presented in Section II were to test the feasibility of inducing luteolysis and an LH surge after intravaginal (IVG) administration of PGF2α and GnRH, respectively. The first experiment of Section I demonstrated that combining data for mRNA expression of interferon stimulated genes in white blood cells and circulating concentration of pregnancy specific protein B is a useful method to identify cows undergoing EM. In addition, only cows undergoing EM after Day 24 of gestation had extended luteal phases but no major alterations to their follicular wave dynamics. Other experiments presented in Section I demonstrated that a resynchronization of ovulation program (Short-Resynch) without the first GnRH treatment 25 ± 3 days after AI, and in which cows were differentially treated based on the ovarian structures present at NPD resulted in a greater proportion of cows re-inseminated at estrus and a similar proportion of pregnant cows when compared with the Ovsynch initiated 25 ± 3 days after AI. In another experiment, Short-Resynch reduced time to pregnancy after first service when compared to blanket use of Ovsynch initiated 32 ± 3 days after AI. Experiments presented in Section II demonstrated that two IVG treatments of PGF2α 12 hours apart caused a decline in progesterone concentration similar to that observed after a single intramuscular luteolytic dose of PGF2α. Further, we observed that IVG instillation of GnRH analogues in combination with citric acid as absorption enhancer elicited an LH surge of similar magnitude than after intramuscular administration of GnRH.