Illness and milk feeding level effects on calf behaviour

A consequence of the high rates of morbidity and mortality of calves on North American dairy farms is the necessity to develop tools for early identification of sickness. As the trend to group-housing increases, the use of automated feeding systems eases the study of feeding behaviour of individual calves within the group. Little is known about the behavioural changes associated with the onset of disease in dairy calves, especially changes in feeding and resting behaviour. The first study of this dissertation examined the effect of milk feeding level on the feeding and resting behaviour of group-housed dairy calves fed with an automated feeding system. In two separate experiments, calves allowed high levels of milk (ad libitum milk replacer and 12 L/d milk) showed reduced frequency of visits to the milk feeder with visits spread throughout the day and a low intake of concentrate until weaning. Low-fed calves (4 L/d milk or milk replacer) had a high frequency of visits to the milk feeder, however the majority of these visits (~ 90%) were unrewarded (i.e. no milk was served) and resulted in increased milk feeder occupancy times compared to high fed calves. Calves fed low levels of milk also spent less time lying down at 4 to 5 wks of age than high fed calves, probably due to the increased number of visits to the milk feeder. No differences in the incidence of illness were found between treatments. These results provide evidence that milk feeding level affects the expression of feeding behaviour, so it must be considered when assessing behavioural changes related to illness. A second study set out to explore the use of a supplemental heat source by sick calves on preference and lying behaviour. During their first 3 d of life calves fed high (12 L/d) or low (4 L/d) levels of milk did not differ in lying times nor did they show differences in preference for the use of the external source of heat. Although no calves were diagnosed with illness during the experiment, calves showed a marked preference for heat, spending more than 50% of their time under heat lamps regardless of environmental temperature fluctuations. In the third study, I set out to determine which behaviours were more susceptible to change in calves afflicted with mild sickness. Calves injected with a mild dose of endotoxin showed a decrease in the time spent at the hayrack, time spent self-grooming and ruminating. Moreover, when sickness was induced, calves showed an increase in the time spent lying and standing inactive. Lastly, the feeding behaviour of naturally sick calves and healthy counterparts fed high or low levels of milk from 4 previous studies was investigated. Sick calves fed high levels of milk showed a decrease in milk intake, visits to the milk feeder and duration of the visits during the day disease was diagnosed and during the subsequent 3 d. Sick low-fed calves only showed a reduction in the duration of the visits to the milk feeder. In conclusion, milk feeding level plays an important role in the understanding of the behavioural changes occuring at the onset of disease. Providing an external source of heat may increase the welfare of newborn calves and may also prove to be a useful tool for identifying sick animals, but further validation studies involving sick calves are needed. Monitoring reductions in milk intake and visits to the automatic feeder in high milk fed calves may be a useful measure in identifiying sick calves. In contrast, other behavioural indicators of activity level, such as standing or lying down, may be more sensitive when identifying sick calves fed low levels of milkLand and Food Systems, Faculty ofGraduat