INFLUENCE OF CATECHOLESTRADIOL ON SHORT-LIVED CORPORA-LUTEA IN BEEF-COWS

The influence of intrauterine administration of catecholestradiol (4-h ydroxylated estradiol) on lifespan of the initial postpartum corpus lu teum was evaluated in suckled beef cows. In experiment 1, postpartum c ows (n=23) were untreated (CONTROL) or received intrauterine infusions (0700 and 1700 hr) of either vehicle (SAL) or catecholestradiol (CATE ; 4 mug) from day 15 to 22 (day 0=parturition). Blood samples were col lected three times weekly (day 15 to 100) and analyzed for progesteron e. In experiment 2, cows received twice daily intrauterine infusions o f either vehicle (n=18), or catecholestradiol (n=19), from day 25 +/- .5 to day 30 +/- .5. Following the final infusion, calves were tempora rily weaned from all cows for 48 hr. At the end of the 48 hr weaning p eriod, cows in each infusion group received either an i.m. injection o f 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 fol lowing calf removal and 3 times weekly through 100 d postpartum. In bo th experiments, the initial postpartum elevation in peripheral progest erone concentrations was characterized as either a short (<5 d) or ext ended (>8 d) luteal phase. In experiment 1, postpartum anestrous inter val (60 +/- 3.4 d) and incidence of short luteal phases (77%) were sim ilar among CONTROL, SAL and CATE treatments. In experiment 2, luteal p hases 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, respectivel y. The incidence of attenuated increases in progesterone, indicative o f short luteal phases was markedly lower (P<.05) in CATE (17%) than SA L+hCG (88%), CATE+hCG (100%) and SAL (100%) treatments. In summary, ca techolestradiol enhanced function and lifespan of the initial postpart um corpus luteum only if administered shortly before expected ovulatio n. If the ovulatory stimulus was timed by administration of hCG, benef icial effects of catecholestradiol were absent.