Stress in dairy calves suckled or not by their dam assessed from cortisol in hair

Summary

Allowing suckling the dam is considered to improve the welfare of calves but separation from the dam at weaning can be highly stressful. We questioned if dairy calves reared with their dam experience more or less stress before and after weaning than calves artificially reared. Cortisol concentration in hair is assumed to reflect stress accumulated over days, weeks or even months. We compared hair cortisol in calves reared or not with their dam. Three groups of 9 calves were used at the INRAE Herbipôle experimental farm: ‘Control’ calves separated from dams immediately after birth and fed with an automatic milk feeder until weaning at 11 weeks of age, ‘Dam’ calves suckled by their dam between morning and evening milking until 11 weeks of age, ‘Mixed’ calves suckled by their dam for 4 weeks then reared as Control calves. Hair samples were taken from each calf's shoulder before weaning (calf age, 60.3 ± 4.3 days) and 30 days after weaning. The hair was washed and dried before cortisol extraction and determination using Salimetrics ELISA kit at the Swedish University of Agricultural Sciences. Hair cortisol concentration was lower in Dam calves than in other calves both before weaning (19.9 pg/mg for Dam calves vs. 26.9 pg/mg; P = 0.02) and after weaning (11.2 pg/mg for Dam calves vs. 15.5 pg/mg; P = 0.08). Before weaning, the Dam calves grazed during the day whereas other calves remained in indoor pens. Cortisol increases with activity and should thus be higher in Dam calves if they were as stressed as the other calves. This reinforces the conclusion that calves with their dam are less stress than calves without their dam. During the week following weaning, Dam calves mooed more than other calves, suggesting intense stress, which did not reduce the difference in hair cortisol with other calves. Despite stress at weaning, rearing dairy calves with their dam seems thus to result in less stress than rearing them without the dam.