Variation in milk cortisol during lactation in Murciano-Granadina goats

Fifty-seven goats were included in an experiment designed to study the effect of lactation stage, parity number, and mammary gland health status on milk cortisol concentration as a method to assess the welfare of Murciano-Granadina goats. The relationships of milk cortisol concentration with different production parameters (milk yield, milk composition, and mechanical milking ability: milk fractioning during milking and milking time) were also studied. The experiment lasted 8 mo and monthly samplings were carried out to determine total milk yield (MY), fractioning during milking (machine milk, MM; machine stripping milk, MSM), and milking time (MT), and a sample was taken from the total milk yield to determine milk cortisol concentration, somatic cell count, and milk composition (fat, protein, and lactose). To determine the infection status of the gland, an aseptic sample was taken for bacteriological analysis before each monthly sampling. Third-parity goats presented higher concentrations of milk cortisol than those of 1, 2, or ≥ 4 parities. Intramammary infection had no effect on milk cortisol concentration, and somatic cell count did not correlate with cortisol concentration. Cortisol presented a significant correlation with MY and MM, but showed no significant correlation with MSM, MT, or milk composition parameters. Variations in milk cortisol concentration in goats may be associated with different physiological factors in the animal (e.g., milk production level, lactation stage, and parity number) and therefore need not always indicate stress for the animal.