Effectiveness of GnRH plus prostaglandin F2alpha for estrus synchronization in cattle of Bos indicus breeding.

Postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding at three locations were studied to determine the efficacy of GnRH + PGF2alpha combinations for synchronization of estrus and(or) ovulation. Cows were equally distributed to each of three treatments by body condition score at the start of the experiment (d 0). All cows received 100 microg of GnRH on d 0 and 25 mg of PGF2alpha 7 d later. The three insemination protocols included 1) AI 12 h after exhibiting estrus during d 7 to 12 of the experiment (Select-Synch; n = 197); 2) timed-AI + 100 microg of GnRH on d 9 of the experiment (CO-Synch; n = 193); 3) AI 12 h after exhibiting estrus during d 7 to 10 of the experiment. Cows not exhibiting estrus by d 10 were timed-AI and injected with 100 microg of GnRH on d 10 of the experiment (Hybrid-Synch; n = 200). The percentage of cows exhibiting estrus during d 7 to 12 of the experiment was lower (P < 0.05) for CO-Synch (17.6%) cows than for Select-Synch or Hybrid-Synch (45.2 and 33.0%, respectively) cows, which did not differ (P > 0.05). For the Select-Synch and Hybrid-Synch cows that exhibited estrus during d 7 to 10 of the experiment and were artificially inseminated, conception rates were similar across treatments (50.5%). Pregnancy rates were greater (P < 0.01) for CO-Synch and Hybrid-Synch (31.0 and 35.5%, respectively) cows than for Select-Synch (20.8%) cows. A greater (P < 0.01) percentage of cycling cows became pregnant (34.5%) than noncycling cows (25.9%) across all treatments. The CO-Synch and Hybrid-Synch synchronization protocols resulted in greater pregnancy rates compared with the Select-Synch protocol in postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding.

Ovulation and estrus characteristics in crossbred Brahman heifers treated with an intravaginal progesterone-releasing insert in combination with prostaglandin F2alpha and estradiol benzoate.

Crossbred Brahman heifers (n = 60) were studied to determine the effect of a 7-d intravaginal progesterone-releasing insert (INSERT) in combination with PG (Lutalyse; 25 mg i.m.) and estradiol benzoate (EB; .5 mg i.m.) on time of ovulation and estrous behavior. In Phase I, heifers at unknown stages of the estrous cycle were assigned by BW and body condition score to one of the three treatments on d 0: 1) INSERT for 7 d and PG on d 7 (CONTROL; n = 10); 2) INSERT for 7 d, PG on d 7, and EB 24 h after INSERT removal (EB24; n = 10); or 3) INSERT for 7 d, PG on d 7, and EB 48 h after INSERT removal (EB48; n = 10). Blood samples were collected every 8 h after INSERT removal. Also, blood sampling and ultrasonography began 8 h after the onset of estrus, determined with HeatWatch devices, and every 4 h thereafter to detect ovulation. In Phase II, Phase-I treatments (n = 10/treatments) were replicated, but only behavioral estrus data were collected to minimize handling of heifers. Frequent handling of heifers did not influence (P > .1) the interval from INSERT removal to the onset of HeatWatch and visual estrus and duration of estrus, so behavioral estrus data were combined for Phases I and II. Interval from INSERT removal to HeatWatch estrus was decreased (P < .05) in EB24 (45.5 h) vs EB48 (55.9 h) and CONTROL (59.2 h). Interval from INSERT removal to ovulation differed (P < .04) between CONTROL, EB24, and EB48 (93.5, 74.5, and 78.9 h, respectively). Ovulatory follicle size was similar (P > .1) between CONTROL, EB24, and EB48 (14.4, 12.5, and 14.1 mm, respectively). Duration of estrus was similar for CONTROL, EB24, and EB48 (14.0, 15.1, and 17.6 h, respectively). No difference (P > . 1) was observed in number of mounts received between CONTROL, EB24, and EB48 (28.0, 25.7, and 39.4, respectively), but number of mounts received increased in Phase II vs Phase I (40.0 and 22.2, respectively; P < .05). In conclusion, EB hastened the interval from INSERT removal to ovulation without altering duration of estrus or number of mounts received. Frequent handling of heifers did not affect interval to first mount received after INSERT removal or duration of estrus, but it decreased the total number of mounts received.