MARÍA JESÚS CARABAÑO2
MOLDI ABDENNEBI 1
1Institute of Arid Regions, Médenine, Tunisia, Faculty of Sciences (F.S.G), University of Gabés, 4119 Gabés, Tunisia
2Depto. De Mejora Genética Animal, INIA, Ctra. De La Coruña Km 7.5, 28040 Madrid, Spain
Abstract - Characterisation of the response in the traits of economic interest to high heat loads is the first step to evaluate the need to introduce adaptation to extreme weather in breeding programmes. The main objective of our study was to evaluate the effect of temperature and humidity on the weightof kids from a Tunisian local goat breed. Growth recording from 2010to 2019 were merged with temperature and humidity data provided by the state meteorological agency. A total of 4,173 body weights in the caprine herd of the Arid Areas Institute of Médenine were used. Different models including alternatively the effects of heat load as a temperature-humidity index (THI), the average temperature (Tavg) and the maximum temperature (Tmax) on weight were used. Heat load on the day of recording or the average heat load of the 7 days previous to the day of weighing (THI7, Tavg7, Tmax7) were tried. Heat load was modelled either as a class effect (c) or through quadratic (quad) or cubic (cub) Legendre polynomials. Overall, 18 models were used. All models included effects of age and weight of dam, the interaction sex*type of birth and year of recording, plus random animal effects. Models using cTHI and cTavg7 provided the best goodness of fit, with Tmax models showing the worst performance. Heat tolerance thresholds were estimated at 21/20, 25/28, 68/66 for Tavg/Tavg7, Tmax/Tmax7, THI/THI7, respectively, from the cubic polynomial fit. Slopes of decay in expected weight after the threshold were around 300 g/degree of Tavg or THI above the threshold. According to these results, heat stress is limiting the growth of kids in this local breed of goats. Tavg and THI seemed to provide a better way of measuring heat load compared with Tmax. Average of heat loads in the period previous to recording of weights showed better results than heat load on the same date, but not for all the studied variables.