RESPONSE OF MILK-YIELD, PLASMA-CORTISOL, AMINO-ACIDS, UREA AND GLUCOSE TO A SINGLE LOW-DOSE ADMINISTRATION OF ADRENOCORTICOTROPIC HORMONE IN LACTATING COWS

An experiment was conducted to determine the effects of a single low-d ose administration of adrenocorticotrophic hormone (ACTH) on milk yiel d, plasma cortisol, free amino acids, urea and glucose in lactating co ws. The animals were treated with either 6 IU synthetic ACTH or 5 mi p hysiological saline (control) administered intravenously via a jugular vein catheter. Blood was withdrawn 60 and 5 min pretreatment (baselin e), and 10, 20, 30, 60, 120, 180, 240, 300, 360, and 420 min post-trea tment. A rapid positive response (P < 0.05) in plasma cortisol occurre d within 10 min of administration of 6 IU ACTH. The maximum increase i n plasma cortisol concentration occurred at 1 h post-ACTH treatment an d plasma cortisol returned to baseline 4 h later. Until 7 d after ACTH administration, no effect on milk yield was recorded. In comparison w ith the saline-treated group, the ACTH-treated group exhibited a signi ficant (P < 0.05) increase in the plasma concentrations of 3-methylhis tidine, glycine, histidine, isoleucine, leucine, lysine, valine, and g lucose. In contrast, the concentrations of alanine, aspartate, glutama te, glutamine and proline decreased significantly (P < 0.05) after ACT H treatment. Hormone administration had no effect on the plasma argini ne, asparagine, methionine, phenylalanine, serine, threonine, tyrosine , and urea. These results demonstrate that the bovine species behaves like other mammalians with respect to its metabolic response to stress . Thus, during stress, ACTH increases adrenal cortical activity which, in turn, stimulates protein catabolism in muscle and gluconeogenesis from some non-essential amino acids.