COMPARISM OF TWO METHODS OF HEAT STRESS PREDICTION IN THREE INDIGENOUS BREEDS OF COWS IN IBADAN

Résumé

Increasing evidence has been shown by meteorologists of a consistent rise in air temperature globally. Among other side effects, heat stress will be induced in livestock species reared in the tropics. The tropics include all the areas on the Earth where the sun reaches a sub solar point, a point directly overhead at least once during the year. It is hot almost year round in these areas and Ibadan, lies in this zone with extended periods of high ambient temperature and humidity. Stress induced by heat severely depresses optimum productivity in all farm animals. In cows, milk secretion, growth rate, reproduction and efficient feed utilization are some of the productive processes impaired. Heat stress has traditionally been measured by physiological data (rectal temperature, respiratory rate, pulse rate, heart rate) while climatic data (temperature, relative humidity) has been used as well either singly or in combination with the former. This study assessed the better predictor of heat stress in indigenous cows using either physiological or climatic data singly and a combination of both methods. Pulse rate, heart rate and rectal temperature in each of the breeds were not significantly different. Average respiratory rate in N'Dama cows (39.54 beats/minute) was however significantly (P<0.05) lower than that in White Fulani (46 beats/minute) and Sokoto Gudali (48.74) cows respectively. This however did not reflect any form of heat stress as it was within the normal physiological range for cows (26-50 beats/minute). The temperature humidity index was 80.73 which showed a mild heat stress condition. It was observed from this study that use of both data gave a more reliable prediction than single use of either. In order for more precise evaluation however, it is suggested that climatic features like solar radiation, day length, wind speed and movement be incorporated into climatic data.