Ovulation and estrus characteristics in crossbred Brahman heifers treated with an intravaginal progesterone-releasing insert in combination with prostaglandin F-2 alpha 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 wi th PG (Lutalyse; 25 mg i.m,) and estradiol benzoate (EB; .5 mg i.m.) on tim e 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 remova l. Also, blood sampling and ultrasonography began 8 h after the onset of es trus, determined with HeatWatch devices, and every 4 h thereafter to detect ovulation. In Phase II, Phase-I treatments (n = 10/treatments) were replic ated, but only behavioral estrus data were collected to minimize handling o f heifers. Frequent handling of heifers did not influence (P > .1) the inte rval from INSERT removal to the onset of HeatWatch and visual estrus and du ration 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 INS ERT removal to ovulation differed (P < .04) between CONTROL, EB24, and EB48 (93.5, 74.5, and 78.9 h, respectively). Ovulatory follicle size was simila r (P > .1) between CONTROL, EB24, and EB48 (14.4, 12.5, and 14.1 mm, respec tively). 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 numb er 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 Pha se I (40.0 and 22.2, respectively; P < .05). In conclusion, EB hastened the interval from INSERT removal to ovulation without altering duration of est rus or number of mounts received. Frequent handling of heifers did not affe ct interval to-first mount-received after INSERT removal or duration of est rus, but it decreased the total number of mounts received.