Studies on serum progesterone levels in Zebu×Holstein heifers during pre- and peripubertal periods

Abstract

The peripheral serum progesterone levels of six normal Zebu×Holstein heifers (75% Holstein inheritance) during the prepubertal period (−150 days) were low (0.23±0.06 ng/ml). They reached maximal values (0.73±0.06 ng/ml) by −45 days (P<0.05 for progesterone values on −90th vs. −45th days) and thereafter decreased to the base level at the time of puberty. The mean (±SEM) age and body weight at puberty of these six heifers were 720±20.70 days and 260.67±8.82 kg, respectively. The serum progesterone levels remained low (0.38±0.17 ng/ml) during early oestrus (up to 28 h) and gradually increased to 2.3±0.84 ng/ml by the 15th day of the cycle.