Heat loss efficiency and thermoregulation responses of Nellore cows

Abstract: Nellore cattle is well adapted to tropical environmental conditions with good thermoregulatory characteristics. However, knowledge related to body temperature regulation and acclimatization mechanisms are still scarce. This investigation aimed to understand the heat loss efficiency and thermoregulation responses of Nellore cows in tropical climate conditions. In this study was used 16 healthy purebred Nellore cows classified by heat loss in efficient and non-efficient using the vaginal temperature continuously monitored by data-loggers. The rectal, tail and ocular temperatures, sweating rate and respiratory frequency were also measured to understand the thermoregulatory responses and correlate to previous classification. In our findings, were noticed that according to heat loss classification the nonefficient cows showed greater amplitude of temperature variation. The body temperature increased from 12:00 PM to 19:00 PM with gradual decreased from 19:00 PM to 07:00 AM, reaching the peak in both groups at around 16:00 PM. In addition, the efficient cows presented higher sweating rate than non-efficient that presented higher rectal temperature, therefore the reduction of body temperature by improving evaporative mechanisms is a good trait of acclimatization to heat. No statistical difference was observed for the other physiological variables between groups. In conclusion, the methodology to classify the cows by heat loss using vaginal data loggers allowed us to distinguish Nellore cows according to their body temperature regulation, being feasible and reproducible. Furthermore, the efficiency to heat loss of this bred was mainly associated with sweating capacity