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1 Animal Sciences Group of Wageningen UR, Division Animal Resources Development, Research Group Animal Welfare, 8200 AB Lelystad, The Netherlands
2 Department of Farm Animal Health, Ruminant Health Unit, Faculty of Veterinary Medicine, Utrecht University, 3584 CL Utrecht, The Netherlands
Corresponding author: B. Beerda; e-mail: bonne.beerda{at}wur.nl.
Increasing milk yields in modern dairy cows cause concern that high yield may impair the cows’ health and welfare, for example, via negative effects on metabolic status and hypothalamo-pituitary-adrenocortical (HPA) function. This study aims to investigate whether a high level of milk production, and the associated metabolic status, affects HPA function in dairy cows and changes their adaptive capacity. Additionally, it aims to establish whether possible effects of milk production level only show under challenging conditions. Holstein-Friesian cows, which produced on average 11,443 and 7727 kg of fat and protein-corrected milk (FPCM)/305 d in their previous lactation, were compared. During the dry period, the cows were fed to requirements or overfed. High milk yield and the concomitant large energy deficit were associated with 1) increased pituitary (re)activity, i.e., increased ACTH baseline concentrations and higher ACTH concentrations after corticotropin-releasing hormone (CRH) administration, and 2) decreased adrenocortical reactivity, i.e., lower cortisol responses after ACTH administration. Although significant, the effects of milk production level on HPA function were relatively small. Animals showed seemingly normal hormonal responses to CRH and ACTH administration. Also, cortisol baseline concentrations were unaffected. It seems, therefore, unlikely that the adaptive capacity of the high-producing cows was significantly impaired compared with their low-producing herdmates.
Key Words: milk production • metabolism • hypothalamo-pituitary-adrenocortical function • adaptive capacity
Abbreviation key: c = control, CRH = corticotropin-releasing hormone, EB = energy balance(s), FPCM = fat- and protein-corrected milk, HP = high producing, HPA = hypothalamo-pituitary-adrenocortical, LP = low producing, nAURC = net area under the response curve, NEB = negative energy balance(s), o = overfed
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