title: Short estrous cycles and associated progesterone in serum of beef heifers aborted at various stages of gestation.
abstract: Estrous cycles were observed and concentrations of progesterone were measured after abortion in crossbred Angus heifers that were injected with a prostaglandin F(2) alpha analogue about day 50 (15 heifers), 75 (14 heifers), 100 (13 heifers) or 125 (49 heifers) of gestation. The average interval from injection to first estrus was 3.6, 4.2, 3.7 and 6.4 d for heifers injected at an average of 50, 75, 100 or 125 d of gestation, respectively. Cycles of fewer than 13 d were classified as short, those of 13 to 16 d as intermediate, those of 16 to 24 d as normal, and those of more than 24 d as long. Heifers aborted at 50 d of gestation had seven short and eight normal first cycles; heifers aborted at 75 d had 11 short cycles, two normal cycles, and one long cycle; heifers aborted at 100 d had 12 short cycles and one normal cycle; whereas heifers aborted at 125 d had 25 short cycles, 13 normal cycles, two long cycles, six intermediate cycles. Three heifers failed to exhibit a second estrus by 50 d after abortion. Of those heifers having short first cycles, short second cycles occurred in one of seven heifers aborted at Day 50, three of 11 at Day 75, seven of 12 at Day 100 and 18 of 25 at Day 125. Serum progesterone was measured at 0, 1 and 2 d after injection and at 5 and 10 d after the first estrus. Concentration of progesterone in serum declined before estrus, then increased by 5 d after estrus in all cases. Progesterone concentration increased between 5 and 10 d after estrus in heifers exhibiting normal estrous cycles but docreased in heifers having short cycles. Data indicate that the percentage of heifers having single or repeated short cycles after abortion increases as the duration of gestation increases to 100 d.
authors.affiliation: Department of Animal Sciences and Industry Kansas State University, Manhattan, KS 66506 USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Wright
authors.forename: G H
authors.initials: GH
authors.lastname: Kiracofe