Developing algorithm for the evaluating of impact of heat stress about dairy cattle crossbred

The aim of this study was to develop an algorithm to predict thermal environment for the creation of crossbred dairy cattle (½, ¾ and ⅞ Holstein-Zebu) and to assess of the impact of heat stress on their physiological parameters and productive performance. The algorithm was developed in the computer program VisuAlg 3.0. The prediction of the thermal environment was made based on the value of temperature and humidity index (THI). For the evaluation of the influence of the thermal stress caused by heat on the physiological parameters and productive performance of dairy cows were estimated based on the value of (THI), the rectal temperature (RT), the Surface Temperature (ST), the decline of the milk production (DMP) and the reducing the food intake of animals (RFI). To test the algorithm we considered the following scenario: air temperature (33°C), relative humidity (60%) and production potential in thermoneutral condition 20kg.cow-1.day-1. The prediction of thermal environment, performed by simulating the algorithm indicates that the animals are submitted to a condition of moderate heat stress, with (THI) 83.92. The rectal temperature and surface temperature values, estimated by the algorithm indicate that animals, regardless of the genetic group, are in thermal stress condition with an increase mean of 0.5°C in the rectal temperature and 1.5°C in surface temperature in relation for the animals created in thermoneutral environment. About the performance of the animals there was a 28.5% reduction in milk production of animals undergoing simulated thermal condition.