Effect of short-term calf removal at three stages of a follicular wave on fate of a dominant follicle in postpartum beef cows

Citation
Be. Salfen et al., Effect of short-term calf removal at three stages of a follicular wave on fate of a dominant follicle in postpartum beef cows, J ANIM SCI, 79(10), 2001, pp. 2688-2697
Citations number
45
Categorie Soggetti
Animal Sciences
Journal title
JOURNAL OF ANIMAL SCIENCE
ISSN journal
00218812 → ACNP
Volume
79
Issue
10
Year of publication
2001
Pages
2688 - 2697
Database
ISI
SICI code
0021-8812(200110)79:10<2688:EOSCRA>2.0.ZU;2-T
Abstract
The hypothesis that ovulation in response to short-term (48 h) calf removal (CR) is dependent on the developmental stage of the dominant follicle was tested in two studies. The objective of Exp. 1 was to characterize the fate of a dominant follicle following 48-h CR on d 2, 4, or 8 of a postpartum f ollicular wave. Ovaries of 61 beef cows were examined daily by transrectal ultrasonography starting at d 20 to 21 postpartum. Treatments were no CR (n = 14) and CR on d 2 (n = 12), 4 (n = 16), or 8 (n = 10) of first detected follicular wave. Percentage of cows that ovulated a dominant follicle follo wing treatment was not different among groups (P = 0.62). Maximum size of d ominant follicles was larger in cows that ovulated (P = 0.002) than in cows that did not ovulate. The objectives of Exp. 2 were 1) to determine whethe r a follicular wave could be synchronized in anestrous cows following injec tion of 1 mg of estradiol benzoate (EB) and 200 mg of progesterone (P-4; EB + P-4); 2) to characterize the fate of dominant follicles following 48-h C R at three stages of a synchronized follicular wave; and 3) to determine wh ether estrous cycles of normal length followed ovulation in cows pretreated with EB + P-4. Ovaries of 50 anestrous beef cows were examined daily as in Exp. 1. Treatments were sesame oil (SO) injected (i.m.) on d 25 postpartum and no CR (n = 9); EB + P-4 and no CR (n = 9); EB + P-4 and CR on 6 (n = 1 2), 8 (n = 9), or 12 (n = 11) d after injection. The EB and P-4 injections were given on d 25 postpartum. Variability in day of emergence of subsequen t follicular waves was lower in cows receiving EB + P-4 than in SO-injected cows (P < 0.05). The percentage of cows that ovulated was not different (P = 0.16), but CR increased the percentage of cows that ovulated when groups that received EB + P-4 were compared to the EB + P-4 group that did not ha ve CR (53.1 vs 11.1%, respectively; P < 0.05). Maximum diameter of dominant follicles was larger (P = 0.05) in ovulatory follicles. The luteal phase w as longer (P < 0.03) in cows receiving EB + P-4 injection (10.6 +/- 1.2 d) than in cows receiving SO (4.4 +/- 2.2 d). In summary, the maximum size of ovulatory follicles was greater than that of nonovulatory follicles, the ov ulatory response of postpartum anestrous cows was maintained through d 8 of a follicular wave, synchronization of follicular waves was accomplished in postpartum cows using EB + P-4, and the subsequent luteal phase length was increased in animals that were administered EB + P-4.