Abstract

Adrenal activity in cattle can be measured by changes in plasma glucocorticoid concentrations. Cows treated with synthetic adrenocorticotrophic hormone (ACTH) to stimulate the adrenal cortex exhibited elevated plasma cortisol concentrations for 4-5h. Concentrations of faecal glucocorticoid metabolites (FGM) peaked between 8-9.5h after ACTH treatment, 2.5 fold higher than basal (P<0.05) and remained elevated for 13h (range, 11.1-16.1h). Faecal glucocorticoid concentrations were monitored in two strains of Holstein Friesian (HF) dairy cows farmed in New Zealand under two systems: NZ pastoral and North American concentrate-based. The overseas (OS) and New Zealand (NZ) HF were fed a pasture-based diet (Grass) or a total mixed ration (TMR) throughout lactation. Faecal samples were collected on four occasions during lactation. Faecal glucocorticoid concentrations of the cows fed Grass were consistently higher (P<0.05) than cows fed TMR. There was also a significant genotype effect; FGM concentrations of the NZ HF cows were higher than OS HF cows (P<0.05). In a separate study, no obvious trends were evident in FGM in NZ HF grazing pasture at three stocking rates (2.2, 3.2, 4.3 cows per hectare). Measuring FGM can be used to monitor acute adrenal activity in cows, but is more difficult to interpret as a measure of chronic stress.

CJ, Morrow, ES Kolver, KA MacDonald, GA Verkerk, and LR Matthews

Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 52-55, 2001