Effects of social and physical stressors on growth hormone levels in dairy cows

Abstract

Plasma concentrations of growth hormone (GH) were studied in 40 Friesian cows in a balanced block design. The cows were assigned to four treatments: (1) control, tie stalls; (2) deprivation of lying from 09:00 to 16:00 and from 22:00 to 05:00, tie stalls; (3) social isolation, tie stalls; (4) slatted floor, crowding in box. Plasma GH concentrations were measured after 23 d of treatment during an 8-h serial blood sampling as well as prior to and after a short test. On day 24, GH response was measured in a serial blood sampling for 0.5 h prior to and for 5 h following intravenous administration of adrenocorticotrophic hormone (ACTH). Deprivation of lying down reduced the level of GH in all sampling series, while no difference was found between treatments 1, 3, and 4. Plasma concentrations of GH prior to and after the test were not different. While concentration of plasma GH of deprived cows did not respond to ACTH challenge, an immediate and transient increase in plasma GH was found in the cows on the other three treatments. Mean plasma concentrations of GH were found to be repeatable between successive days. The results demonstrate that alterations in GH levels, among others, may be a valuable indicator of the biological cost of different environmental challenges. Key words: Dairy cows, stress, ACTH, GH release