Nycthemeral changes in plasma cortisol levels in preruminant calves with different milk proteins.

Preruminant calves bearing indwelling catheters in the hepatic artery, the portal and the hepatic veins were fed with two kinds of diets, a conventional curdled milk diet and a milk diet which was uncurdled in the abomasum. Measurements of plasma cortisol in blood sampled regularly during the 24 hr of the day indicated that with curdled milk, cortisol concentrations were significantly higher than with uncurdled milk. Nycthemeral changes were characterized by high values before meals and by postprandial decreases. Between meals, several peak values were observed and in the night a regular increase occurred. With both kinds of meals, cortisol evolutions were similar though peak values were higher with the curdled milk.