Adrenal responsiveness to a low-dose ACTH challenge in early and late lactating dairy cows

Abstract

To improve the evaluation of the chronic stress conditions, the adrenal responsiveness to low dose ACTH stimulation, in different lactation stages, was checked in 56 multiparous dairy cows from 2 herds (25-350 days in milk). Cows were retrospectively ranked in 3 stages: early (<75) average (75-150) and late (>150 DIM) lactation. Herd B (vs. herd A) showed higher basal cortisol and frequency of inflammation. Early stage (vs. others) showed higher basal cortisol, bilirubin, ceruloplasmin and haptoglobin, as well as lower ones of cholesterol and lower rise of plasma cortisol during ACTH challenge (P<0.001). Cortisol peak was also correlated negatively with ceruloplasmin, bilirubin, ROM, and positively with cholesterol, vitamin A and E. Both, basal cortisol and cortisol response to ACTH, are associated to inflammation but in opposite way: basal cortisol positively and cortisol response negatively. This latter results are likely due to lower transcortin synthesis, that could be ensued in early lactating cows suffering inflammation.