title: Effect of short-term calf removal at three stages of a follicular wave on fate of a dominant follicle in postpartum beef cows.
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 follicular 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 following treatment was not different among groups (P = 0.62). Maximum size of dominant 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 whether a follicular wave could be synchronized in anestrous cows following injection of 1 mg of estradiol benzoate (EB) and 200 mg of progesterone (P4; EB + P4); 2) to characterize the fate of dominant follicles following 48-h CR at three stages of a synchronized follicular wave; and 3) to determine whether estrous cycles of normal length followed ovulation in cows pretreated with EB + P4. 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 + P4 and no CR (n = 9); EB + P4 and CR on 6 (n = 12), 8 (n = 9), or 12 (n = 11) d after injection. The EB and P4 injections were given on d 25 postpartum. Variability in day of emergence of subsequent follicular waves was lower in cows receiving EB + P4 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 + P4 were compared to the EB + P4 group that did not have 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 was longer (P < 0.03) in cows receiving EB + P4 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 ovulatory 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 + P4, and the subsequent luteal phase length was increased in animals that were administered EB + P4.
authors.affiliation: Department of Animal Sciences, University of Missouri-Columbia, 65211-5300, USA.
authors.forename: B E
authors.initials: BE
authors.lastname: Salfen
authors.forename: F N
authors.initials: FN
authors.lastname: Kojima
authors.forename: J F
authors.initials: JF
authors.lastname: Bader
authors.forename: M F
authors.initials: MF
authors.lastname: Smith
authors.forename: H A
authors.initials: HA
authors.lastname: Garverick
mesh_terms: D000780:Anestrus; D000818:Animals; D000833:Animals, Suckling; D002417:Cattle / Q000502:physiology*; D004334:Drug Administration Schedule; D004958:Estradiol / Q000008:administration & dosage* / Q000031:analogs & derivatives*; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000502:physiology*; D010062:Ovulation Induction / Q000662:veterinary; D049590:Postpartum Period; D011374:Progesterone / Q000008:administration & dosage*; D013997:Time Factors; D014463:Ultrasonography; D014886:Weaning
chemical_list: C074283:estradiol 3-benzoate; D011374:Progesterone; D004958:Estradiol