Influence of catecholestradiol on short-lived corpora lutea in beef cows

Abstract

The influence of intrauterine administration of catecholestradiol (4-hydroxylated estradiol) on lifespan of the initial postpartum corpus luteum was evaluated in suckled beef cows. In experiment 1, postpartum cows (n=23) were untreated (CONTROL) or received intrauterine infusions (0700 and 1700 hr) of either vehicle (SAL) or catecholestradiol (CATE; 4 μg) from day 15 to 22 (day 0 = parturition). Blood samples were collected three times weekly (day 15 to 100) and analyzed for progesterone. In experiment 2, cows received twice daily intrauterine infusions of either vehicle (n=18), or catecholestradiol (n=19), from day 25 ± .5 to day 30 ± .5. Following the final infusion, calves were temporarily weaned from all cows for 48 hr. At the end of the 48 hr weaning period, cows in each infusion group received either an i.m. injection of 1,000 IU hCG (SAL+hCG, n=9; CATE+hCG, n=9) or no further treatment (SAL, n=9; CATE, n=10). Blood samples were collected daily for 21 d following calf removal and 3 times weekly through 100 d postpartum. In both experiments, the initial postpartum elevation in peripheral progesterone concentrations was characterized as either a short (<5 d) or extended (>8 d) luteal phase. In experiment 1, postpartum anestrous interval (60 ± 3.4 d) and incidence of short luteal phases (77%) were similar among CONTROL, SAL and CATE treatments. In experiment 2, luteal phases were induced within 10 d of onset of weaning in 90, 100, 56 and 60% of cows in SAL+hCG, CATE+hCG, SAL and CATE treatments, respectively. The incidence of attenuated increases in progesterone, indicative of short luteal phases was markedly lower (P<.05) in CATE (17%) than SAL+hCG (88%), CATE+hCG (100%) and SAL (100%) treatments. In summary, catecholestradiol enhanced function and lifespan of the initial postpartum corpus luteum only if administered shortly before expected ovulation. If the ovulatory stimulus was timed by administration of hCG, beneficial effects of cathecholestradiol were absent.