Manipulating ovarian function and uterine health with the aim of improving fertility in dairy cattle

The objectives of this dissertation were to determine reproductive management strategies and hormonal manipulations of ovarian responses to optimize fertility of dairy cattle and to investigate the efficacy of treatments of uterine diseases and its subsequent effects on fertility of dairy cows. An additional objective was to determine mechanisms of induced infusion with T. pyogenes on length of the estrous cycle.;Chapter 3 describes effects of 1 (1TAI) or 3 timed AI (3TAI) before natural service in lactating dairy cows not detected in estrus on pregnancy, and revealed that 3TAI had greater hazard of pregnancy and 21-day cycle pregnancy rate than 1TAI.;Chapter 4 evaluated the effects of the first gonadotropin-releasing hormone (GnRH) injection of the 5-d timed AI program on ovarian responses and pregnancy per AI (P/AI) and the effect of timing of the final GnRH to induce ovulation relative to AI on P/AI in dairy heifers. Use of GnRH on the 1st day of the 5-d timed AI program resulted in low ovulation and no improvement in P/AI when a single prostaglandin (PG) F2alpha injection on d 5 was used. Extending proestrus by delaying the final GnRH from 56 to 72 h concurrent with AI benefited P/AI of heifers not in estrus at AI.;Chapter 5 investigated the effects of GnRH at the initiation of the 5-d timed AI program combined with two injections of PGF2alpha on ovarian responses and P/AI in dairy heifers, and the role of progesterone on LH release and ovulation in response to GnRH. Increased ovulation with GnRH given at initiation of 5-d timed AI program combined with two doses of PGF2alpha on d 5 and 6 optimized P/AI. High progesterone at GnRH administration suppressed LH release and impaired ovulation.;Chapter 6 investigated the efficacy of PGF2alpha as a therapy to reduce the prevalence of subclinical endometritis and to increase P/AI in cows subjected to a timed AI program. The results of this study revealed that treatments with PGF2alpha before initiation of the timed AI program were unable to improve uterine health and P/AI.;Chapter 7 investigated if intrauterine infusion of T. pyogenes influence uterine expression of genes related to inflammation, luteolytic cascade and luteal lifespan. Although T. pyogenes reduced luteal lifespan in half of the cows, only minor changes in uterine gene expression were identified.;Chapter 8 investigated the efficacy of ampicillin trihydrated for treatment of metritis and subsequent effects on fertility. Ampicillin was an efficacious therapy for metritis but had no differential effects on P/AI when compared with ceftiofur hydrochloride.