prostaglandin F2αfor lactating dairy cows with silent estrus

Two experiments were conducted in 17 dairy herds in NE Kansas to determine the effectiveness of prostaglandin F2α(PGF) for reducing intervals to conception for cows with silent or unobserved estrus. Cows that failed to be seen in heat so they could be inseminated after calving (Exp. 1) and cows that did not return to estrus after AI and were not pregnant when presented to veterinarian for pregnancy examination (Exp. 2) were assigned alternately to be given PGF or to receive no treatment after detection of a palpable corpus luteum. Cows were inseminated at 72 and 96 hr after PGF treatment if not detected in heat. Intervals from treatment to conception were reduced after PGF treatment. Cows with unobserved estrus can be inseminated sooner and have shorter intervals to conception if PGF is used for reproductive management in association with a routine herd health program.; Dairy Day, 1984, Kansas State University, Manhattan, KS, 1984;

Summary Two experi ments were conducted in 17 dairy herds in NE Kansas to determine the effecti veness of prostaglandin F2 (PGF) for reducing intervals to conception for cows with silent or unobserved esnus. Cows that failed to be seen in heat so they could be inseminated after calving (Exp. 1) and cows that did not return to estrus after AI and wel'e not pregnant when presented to veterinarian for pregnancy examination (Exp. 2) were assigned alternately to be given PGF or to receive no treatment after detection of a palpable corpus luteum. Cows. were. inseminated at 72 and 96 hI' after PGF treatment if not detected in heat. Intervals from treatment to conception wel'e reduced after PGF treatment. Cows with unobserved estrus can be inseminated sooner and have shorter intervals to conception if PGF is used for repI'oducti ve management in association with a routine herd health program.

Introduction
Intervals from cal ving to conception longer than 120 days are an economic liability to dairy producers. Failure to detect estl'US is the primary reason for lengthy calving intervals rather than a COWlS failUI'e to conceive once inseminated. Missed heats occur in cows with delayed intervals to first service and in cows that do not concei ve when bred and do not return to estrus approximately 3 wk after AI. Prostaglandin F 2 (PGF) is a potential solution to dealing with dairy cows with "I 0.
SI ent or unobserved estrus. I j; 1We acknowledge the donation of prostaglandin F 2.a (Lutalyse®) and partial financial support provided by The Upjohn Company, Klilamazoo, MI.

Procedures
Exp. 1. Dairy cows (n=223) that had not been observed in heat and bred by at least 6 wk postpartum were presented to hel'd veterinarians at a routine herd visit. Those cows with a palpable corpus luteum were assigned alternately to be an untreated control or to receive PGF (5 cc Lutalyse®). Cows were inseminated when observed in heat. If heat was not detected by 72 hI' after PGF J cows were inseminated at 72 and 96 hr. If cows showed heat after 96 hI' J they were reinseminated.
Exp. 2. Cows (n=85) with unobserved estrus after insemination and diagnosed open at pregnancy examination were assigned to a control or PGf treatment group as in Exp. 1 if a corpus luteum was palpated. Cows were inseminated as described for Exp. 1.

Results and Discussion
Exp. 1. Intervals from treatment to heat J first service, and conception were shorter (P<.Ol) for cows recei ving PGF than for controls (Table O. Conception occurred 22 days earlier (P<.Ol) for treated cows than for controls. First service conception' and cu mulati ve pregnancy rate were si milar for control and treated cows. • Exp. 2. Intervals from treatment to estrus and first service were shorter (P<.OI) for treated cows compared with controls (Table 2). Time from treatment to conception tended to shorter by 16.5 days for cows gi ven PGF compared with controls. As in Exp. 1, first-service conception and cumulative pregnancy rates were similar between groups • a Less than control (P<.Ol).

Recommendations
Treating unobserved or silent estrus with PGF will reduce conception intervals. If a corpus luteum is present, treat cows with 5 cc lutalyse$ or 2 cc Estrumate~. Observe for estrus and AI when detected in heat. If no estrus is observed by 72 hr after treatment, AI cows at 72 hr and again at 96 hr. If cows show heat after 96 hr, rebreed. It is essential to bred cows at 72 and 96 hr in the absence of detected estrus for maxi mal results. til • )I. . '