In artificial rearing, calves are separated from their dam usually within 24h after birth
and any further social contacts to the mother are prevented. Although this is common
in practice we expect severe consequences on the health state, weight gain and
stress response of the young calf. Two groups of calves suckled by their mother (unrestricted
contact, n=14; contact twice daily for 15 minutes each before milking, n=15)
were compared to two control groups that were both fed via automatic milk feeder
(maximal six times daily, n=14; twice daily, n=14). The calves of the four treatment
groups were kept in the same barn and cows were milked twice daily. All calves were
weaned at 13 weeks of age. The calves were weighed weekly until 3 weeks after
weaning. The health state of each animal was assessed daily and all veterinary treatments
were recorded until weaning. Stress response to a long-term stressor (absence
of the mother) was assessed by stimulation of the HPA axis by ACTH administration
(at 11 weeks of age). For statistical analyses, linear mixed-effects models were used.
The health state of both suckled groups was poorer (p=0.046, caused by diarrhoea),
but the number of animals that had to be treated by a veterinarian did not differ. During
the milk feeding period, weight gain was better in suckled calves (p<0.001). After
weaning, the weight gain of all treatment groups was diminished, especially in suckled
calves (p<0.001). Cortisol response to ACTH administration was reduced in calves fed
via an automatic milk feeder (p<0.001). The higher weight gain in suckled calves
before weaning can be explained by the large milk amounts the calves received.
These results suggest that suckled calves show fewer signs of chronic stress. We
conclude that rearing without contact with the mother causes chronic stress in young
calves in terms of desensitization of the HPA axis
