Pregnancy Rates Per Artificial Insemination for Cows and Heifers Inseminated at a Synchronized Ovulation or Synchronized Estrus

摘要: Two synchronization protocols were tested for lactating dairy cows and heifers. Nulliparous heifers (13 to 23 mo; n = 155) primiparous multiparous (60 289 d postpartum; 310) assigned randomly two treatments. Controls received 25 mg of PGF2a artificially inseminated according the a.m.‐p.m. rule following detected estrus. All controls that not in estrus injected with at 14-d intervals until artificial insemination (AI) a or timed AI 72 80 h after third sequential injection PGF2a. Treated protocol used GnRH synchronize ovulation (Ovsynch). Cows treated Ovsynch i.m. 100 random stage estrous cycle. Seven days later, this group PGF 2a, followed by second 30 36 later. Subsequently, 16 20 GnRH. Pregnancy rates per similar (38.9% vs. 37.8%) control protocol, respectively. However, pregnancy rate was greater (74.4%) than (35.1%). Evaluation serum progesterone concentrations each hormonal indicated first synchronized luteal function but In summary, one fixedtime provided as did a.m.‐ p.m. had been induced cows, fixed-time effective because lack synchronization.