Effects of grain processing and bovine somatotropin on metabolism and ovarian activity of dairy cows during early lactation

This study compared the effects of exogenous bovine somatotropin (bST) on t he metabolism and ovarian activity of cows fed diets differing in ruminally degradable starch. Twenty-four multiparous and eight primiparous Holstein cows in early lactation were divided into four groups and fed diets contain ing 39% grain as steam-flaked sorghum or steam-rolled corn with or without bST for 90 d in a 2 x 2 factorial design. Flaked sorghum improved energy st atus of cows during early lactation, tending to increase plasma glucose and insulin. Administration of bST decreased plasma urea nitrogen and increase d nonesterified fatty acids (NEFA). Plasma levels of beta-hydroxybutyrate ( BHBA) and hepatic concentrations of triglycerides were not altered by treat ments. Temporal changes in plasma glucose, urea nitrogen, NEFA, and BHBA we re detected in a quadratic manner and insulin increased linearly with time, but treatments did not affect postpartum changes in these metabolites. The re were greater decreases in body weight and net energy balance in cows on bST during the first 7 wk of treatment. Cows receiving bST took longer to r each the nadir of negative energy balance, and bST tended to delay the peri od to reach a positive energy balance. Follicular populations and incidence of cystic ovaries were not affected by treatments, but cows receiving bST had fewer double ovulations. Flaked sorghum increased plasma progesterone d uring the early luteal phase of the first two postpartum estrous cycles. Fe eding more ruminally degradable starch improved the energy status and lutea l activity of cows in early lactation.