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

Abstract

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 2×2 factorial plan for 7 days. There were no feeding×lying interactions, and feeding level did not affect plasma cortisol concentrations, adrenocorticotrophic hormone (ACTH) and cortisol responses to challenge with 15 μg corticotrophin-releasing hormone (CRH), or ACTH and cortisol responses to CRH following the administration of 0.3 mg dexamethasone. Compared with free-lying animals, lying-restricted cows had increased basal plasma cortisol concentrations, and reduced ACTH and cortisol responses following CRH 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.