REPRODUCTIVE PATTERNS OF THE YAK .3. LEVELS OF PROGESTERONE AND ESTRADIOL-17-BETA DURING PREGNANCY AND THE PERIPARTURIENT PERIOD

Changes in plasma progesterone and oestradiol-17β in yaks during pregnancy and the periparturient period of yaks and in milk during the first month of pregnancy were analysed. The profiles of progesterone were similar for pregnant and non-pregnant yaks within 14 days following oestrus (P>0.05), but the concentration was significantly higher on day 19 (P<0.05) and in pregnant yaks tended to increase gradually thereafter. The plasma progesterone decreased rapidly on day 120 (P<0.05), then increased to reach its maximum of 15.5 (sd3.74) ng ml-1 on day 210; declined again 20 days before parturition and resumed the same levels at parturition as during mating (P>0.05). The oestradiol-17β levels in plasma and milk increased gradually from day 23 after conception, decreased abruptly on day 60 (P<0.05), then increased to reach their maximum at parturition of 551.4 (sd 70.86) pg ml-1. The oestradiol decreased again after parturition to the same level as during mating (P>0.05). © 1993 BailliÈre Tindall.