Prolactin response in beef cows and heifers suckling one or two calves

Publisher Website
Google Scholar
Abstract
Blood was collected, at 5 min intervals for 3 h, via jugular cannulation every 14 days during the first 4 mo. post partum from beef cows and heifers, 4 suckling 2 calves and 4 suckling 1 calf. Calves were isolated from the dams to prevent suckling for .apprx. 4 h before and 2 1/2 h during sampling to obtain baseline values for prolactin, measured by radioimmunoassay. During the last 30 min of sampling, calves were allowed to suck. Milk samples were also collected at 28 day intervals from 60 females, 30 with twins and 30 with single calves, beginning 2 wk after calving and continuing until calves were weaned at 180 days of age. No differences were observed between dams with 1 and 2 calves for baseline plasma prolactin level or for prolactin response to the suckling stimulus by 1 or 2 calves. Milk prolactin concentration was significantly higher (P < 0.01) for dams with 2 calves, probably reflecting the more frequent suckling that occurs with twins. Milk prolactin value in this study was not highly correlated with the post partum interval to 1st ovulation from another study on these animals. Prolactin evidently is not the primary factor controlling the longer post-partum interval to 1st ovulation in beef cattle with twins.