Effects of Feeding Frequency and Exogenous Somatotropin on Lipolysis, Hormone Profiles, and Milk Production in Dairy Cows

¹ Department of Animal Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5

Effects of feeding frequency and exogenous bovine somatotropin on lactational performance and hormone profiles were examined with 12 multiparous Holstein cows. At 45 d postpartum, cows were assigned to one of two feeding systems. Concentrates were offered in two equal portions at 0800 and 1600 h or in 12 equal portions at 2-h intervals. Chopped alfalfa hay (2.6 kg/d) and barley silage (ad libitum) were fed at 0900 and 1500 h. At 136 d postpartum, cows within each feeding frequency were assigned in a single crossover design to injection of 30 mg of bST/d or solubilization vehicle. Feeding frequency did not influence any of the parameters measured nor did bST interact with feeding frequency. Somatotropin injection increased daily milk yield of cows by 4.4 kg and concentrations of fat and lactose in milk. Protein concentration and fatty acid composition of milk were not influenced by bST injection. Average plasma somatotropin concentrations were elevated threefold, peak concentrations were increased sevenfold, and concentrations at 48 h postinjection were 1.5 times control values. Plasma insulin concentrations were decreased by bST treatment. Results indicate that responses to short-term bST injection are not influenced by feeding frequency.

Key Words: feeding frequency • somatotropin • dairy cow

Submitted on August 11, 1989
Accepted on January 12, 1990