Extent and economic effect of heat loads on dairy cattle production in Australia

Objective To investigate the extent of heat load problems, caused by the co mbination of excessive temperature and humidity, in Holstein-Friesian cows in Australia. Also, to outline how milk production losses and consequent co sts from this can be estimated and minimised. Procedures Long-term meteorological data for Australia were analysed to det ermine the distribution of hot conditions over space and time. Fifteen dair y production regions were identified for higher-resolution data analysis. B oth the raw meteorological data and their integration into a temperature-hu midity thermal index were compiled onto a computer program. This mapping so ftware displays the distribution of climatic patterns, both Australia-wide and within the selected dairying regions. Graphical displays of the variati on in historical records for 200 locations in the 15 dairying regions are a lso available. As a separate study, production data from research stations, on-farm trials and milk factory records were statistically analysed and co rrelated with the climatic indices, to estimate production losses due to ho t conditions. Results Both milk yields and milk constituents declined with increases in t he temperature-humidity index. The onset and rate of this decline are depen dent on a number of factors, including location, level of production, adapt ation, and management regime. These results have been integrated into a far m-level economic analysis for managers of dairy properties. Conclusion By considering the historical patterns of hot conditions over ti me and space, along with expected production losses, managers of dairy farm s can now conduct an economic evaluation of investment strategies to allevi ate heat loads. These strategies include the provision of sprinklers, shade structures, or combinations of these.