Shelter studies using thermal models of cattle
The specification of shelter requirements of cattle requires knowledge of the complex interactions of climate, the enclosed animals and their enclosure. The modelling approach used in this research reduces this complexity by identifying the most significant components of the system. Four electrically heated physical thermal models of suckler cows with controlled internal temperatures and coverings of synthetic hair were used over two consecutive winter periods to simulate sensible heat losses from suckler cows kept in an unsheltered site and in three simple shelters. The measured reductions of unsheltered heat losses were (1) 2% (2) 6% and (3) 20% for shelters with respectively (1) just a roof (2) four solid walls, no roof and (3) a roof and four walls with ventilation openings. A mathematical model which predicts hourly and daily mean sensible heat losses from a suckler cow using measurements of air temperature, rainfall, windspeed and net radiation had previously been developed using a large thermal model. Climate modifying factors were derived for each shelter type by comparing hourly and daily mean measured heat losses with those predicted by the mathematical model. These factors were successfully validated using the second winter's data. The accuracies of heat loss predictions for the small thermal models in each shelter were similar to those for the original large thermal model. Examples are given for cattle sheltered by a forest and for calves sheltered by a creep to show how this model for prediction of heat losses in different shelters can be incorporated in a model of the whole system. Meteorological Office climate data was used to predict heat losses from cattle. This included a novel method for prediction of net radiation. The analysis indicated that predictions for a given site could be applied to a large area although this should be tested before any large scale analysis of records is undertaken.