The effects of feed restriction and lying deprivation on pituitary-adrenal axis regulation in lactating cows

In order to examine the effects of moderate feed restriction and periodic lying deprivation on pituitary-adrenal axis function in lactating dairy cows, 32 non-pregnant Jersey cows were allocated to two levels of feeding (4% vs. 3% of body weight of dry matter daily) and lying restriction (free lying vs. prevention of lying from 15:00 to 06:45 h daily) in a 2 X 2 factorial plan for 7 days. There were no feeding X lying interactions, and feeding level did not affect plasma cortisol concentrations, adrenocorticotrophic hormone (ACTH) and cortisol responses to challenge with 15 mug corticotrophin-releasing hormone (CRII), or ACTH and cortisol responses to CRH following the administration of 0.3 mg dexamethasone. Compared with free-lying animals, lying-restricied cows had increased basal plasma cortisol concentrations, and reduced ACTH and cortisol responses following CRII challenge relative to pre-challenge baselines. Lying-restricted cows also had an increased plasma cortisol/ACTH ratio for the total area under the hormone response curves following CRH. Dexamethasone administration prior to CRH challenge produced a similar result to CRH challenge alone, indicating that there were no differences between lying-restricted and free-lying cows in negative feedback sensitivity of the pituitary to glucocorticoids. In conclusion, 7 days of moderate feed restriction did not appear to alter pituitary-adrenal axis function, whereas periodic lying deprivation reduced pituitary responsiveness to CRH and increased plasma cortisol/ACTH ratio following CRH challenge. (C) 2002 Elsevier Science B.V. All rights reserved.