Abstract
This chapter describes the growth hormone (GH) release in calves selected for high and low dairy merit. The possible association between growth hormone release and dairy merit was studied using four provocative tests in British Friesian calves from lines selected for high and low milk yield. Animals were tested in 5 batches with each calf receiving 3 of 4 tests. Blood was sampled via jugular cannulae at −15, −5, 5, 10, 15, 20, 30, 60, 90, 120 min relative to injection. Serum was kept frozen until assayed by RIA for GH. Response was measured as the mean value during 5, 10, 15, 20 min following injection of GRF. TRH and GRF + TRH and 15, 20, 30, 60 min following arginine injection. Data were analyzed in logarithmic scale and adjusted for effects of sex, batch, and diet. The difference in GH response was consistently higher in the high animals although the difference was only significant after the GRF injection. High animals also tended to have higher baseline concentrations. These findings indicate that GH release may be an indicator trait of breeding value for milk yield and thereby be of special value in MOET selection schemes.
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