Assessment of heat stress in dairy cattle in Papua New Guinea.

The effects of breed (Friesian, AIS, Sindi-Sahiwal and Jersey), time of day (am v pm) and season of the year (hot or cool) on rectal temperature, pulse rate and respiratory rate were examined in the Highlands and Lowlands of Papua New Guinea. Two types of variation were investigated. Between-cow variation was the basis for the comparison of sites, seasons and breeds. Between-day variation was used to assess the effect of environmental temperatures on the animal parameters. Respiration rate and rectal temperature appeared more sensitive as indicators of heat stress than pulse rate and using these criteria the highlands climate was suitable for dairy cattle. Jerseys and Sahiwals showed lower respiratory rates compared with Friesians and AIS and their increase in rectal temperature during the day was less than the other two breeds but was not significantly so. The relationships between respiration rate and rectal temperature are discussed.