Sleep and rest in calves - relationship to welfare, housing and hormonal activity

Adequate rest and sleep is essential for the welfare of young growing animals. Sleep regulates the secretion of several hormones and is essential for brain development. Lying deprivation affects the pituitary-adrenal axis in bulls and reduces GH secretion in dairy cows. Several environmental factors are thought to affect calves' sleep and rest. The effects of housing or management on the sleep of farm animals is therefore of concern regarding the animals' welfare. The rhythms of rest and activity of calves have been proposed as potential measures of the extent to which farm animals have adapted to their environment. Thus far, however, very little systematic work has been conducted in order to identify and understand the meaning of resting behavior for calves.

In this dissertation, a non-invasive method to register sleep electrophysiologically from young calves was developed, and the electrophysiological findings were validated against their resting behavior to find the best behavioral estimates for identifying sleep phases. Also, the effects of potential environmental stressors on calves' resting behavior were studied. Calves' GH and cortisol secretion patterns were followed after relocation or housing on softer or harder floor types.

In conclusion, electrophysiological data can be recorded non-invasively from freely moving, group-housed calves, and observations of resting behavior can identify when calves are asleep, although further work is needed to use behavior to identify the phases of sleep. The calves effectively maintain their total resting time under several potential environmental stressors such as low temperature, isolation, and hard flooring. Aging and environmental conditions mainly affect the proportions of different resting postures rather than the total time spent resting. As with the resting behavior, stressors such as relocation or floor type do not easily affect the levels of rest-related hormones such as cortisol and GH. Consequently, resting time may not be a sufficiently sensitive measure of environmental quality in young calves, unless the environment is very stressful. To identify those environmental factors which may disturb calves' sleep or rest will require additional research.