Factors associated with the housing environment of calves in relation to the prevention of respiratory disease

Abstract

Respiratory disease is a multifactorial disease that is a major cause of morbidity and mortality in calves. The main emphasis of this thesis is surrounding the housing environment and its effect on the calf during the pre-weaning phase of life. The housing environment can affect disease levels as well as general performance in calves. An important physical aspect of calf housing is ventilation as it allows the removal of airborne microorganisms, particulate matter and moisture from the air. In the first instance, the best method is to prevent the generation of such fomites. In this work, the factors of the quality of straw bedding material and presence of calves were analysed for the outcomes of particle and total bacterial count. Results showed that the presence of calves can increase the levels of particles and total bacterial count. This study showed that there was no effect of straw quality on particulate matter and total bacterial count within the range of straw types used.

Within the calf housing, there can be areas of the microclimate that can cause the calf to display a response such as removing itself from the hostile environment. This behavioural response was examined in relation to specific air temperature (5oC, 10oC, 15oC) and wind speed combinations (0m/s, 1m/s, 3.3m/s). Overall it was found that calves showed an aversion to increasing wind speed and that there was no significant effect of air temperature on any of the behavioural measures.

The calf is exposed to naturally occurring variations in air temperature, wind speed and air quality on a daily, and occasionally hourly, basis during this vulnerable period of life. The ramifications of being exposed to such variations in terms of calf growth in the first month of life were examined in a longitudinal study of 299 dairy and dairy cross beef calves over one year. A longer period of exposure to temperatures below the lower critical temperature for calves had a significant effect on the daily liveweight gain.

The variation in environmental conditions provides potential stressors to the young calf which can increase the susceptibility to disease. An indicator of respiratory disease is an elevation in core body temperature which is normally assessed by taking a rectal temperature measure. As part of this work, a non-invasive method for temperature acquisition was explored. The association between rectal temperature and the temperature obtained from thermal imaging the area surrounding the medial canthus was established as being weak. Despite incorporating the environmental factors that influenced the thermal image temperature (air temperature and wind speed) into a predictive model, there was only a very minor improvement in the relationship but not enough to establish thermal imaging as a reliable method for obtaining the core body temperature of calves. Although repeatable, the temperature gained from thermal imaging may phenotypically not reflect core body temperature.

In conclusion, this thesis has provided supporting evidence to accentuate specific aspects of calf housing such as protection from draughts at calf level and the identification of risk factors in terms of air quality. It also highlights the impact the housing environment can have on the growth of the calf pre weanin