Abstract
The objective was to evaluate vaginal temperature as a thermoregulatory response of Nellore heifers under different microclimatic conditions. The study was conducted during one year in an experimental area located at 54°37′W, 20°27′S, and 530 m of altitude in Brazil. Twenty-four Nellore females were reared in integrated crop-livestock-forestry systems with different shading patterns. The randomized complete block experimental design was utilized with a sub subdivided plots scheme, with plot corresponding to the production systems, the subplot to the season of the year, and the sub subplot, the hours of the day. To characterize the microclimate, data regarding air and black globe temperatures, and air relative humidity were collected and from them, temperature-humidity index was calculated. Vaginal temperature was obtained by using a bottom-type temperature logger (i-button) attached to an adapted intravaginal device. The black-globe temperature explained the variation on vaginal temperature. Increases on vaginal temperature were only observed, on average, two hours after the increase of black-globe temperature. The microclimatic conditions found in the systems, resulting from the various tree densities, modify the vaginal temperature in different degrees, demonstrating that the shading effect is not always accompanied by improvements in thermal comfort. The system with intermediate density showed a better microclimatic condition and, consequently, a lower increase in vaginal temperature. The interaction between air temperature, humidity and solar radiation resulted in adverse environmental conditions, however, Nellore heifers showed good adaptation to the environment. In conclusion, vaginal temperature is a good indicator to evaluate the thermoregulatory response in Nellore heifers.
Highlights
One of the limitations found in tropical beef cattle systems is the negative effect of heat stress on the productive indexes
Weak and positive correlations were observed with air temperature and dew point temperature, and very weak and positive correlation with black globe temperature and humidity index (BGHI)
Vaginal temperature and thermoregulatory response in Nellore heifers under different microclimatic conditions correlation with vaginal temperature, highlighting the strong correlation observed with black globe temperature
Summary
One of the limitations found in tropical beef cattle systems is the negative effect of heat stress on the productive indexes. Heat tolerance in cattle has been increasingly used as a selection tool for adaptation to more inhospitable regions. There are factors related to the environment, which involve climatic elements, and factors related to the animal, such as the physiological responses associated, mainly, with the thermoregulatory mechanism [2]. Attempts to establish criteria for classification of animals less or more adapted to particular environments, as well as to characterize the environment according to their thermal comfort condition, have been increasingly explored, since there are differences in the intensity of responses to adversities between species, breeds, and even individuals. Indexes related with climatic elements have been used as a tool to evaluate the environmental condition in which the animal is reared [1]
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