02590nam a2200253 a 450000100080000000500110000800800410001910000200006024501260008026001790020652017460038565000130213165000160214465000100216065000200217065000100219065000110220065000160221165300190222765300240224670000290227070000210229970000160232015329722025-01-30       2006    bl uuuu     u00u1 u    #d1 aFINOCCHIARO, R.  aGenetic and environmental components of susceptibility to heat stress n mediterranean dairy sheep.h[electronic resource]  aIn: WORLD CONGRESS ON GENETICS APPLIED TO LIVESTOCK PRODUCTION, 8., 2006, Belo Horizonte, MG. Proceedings... Belo Horizonte: Instituto Prociência, 2006. 4 f. 1 CD-ROM.c2006  aMediterranean countries are characterized by exposure to considerable heat between three and six months annually. High ambient temperature, solar radiation, wind speed and relative humidity, cause the effective temperature of the environment to be above the thermo-neutral zone of the animals (5 to 25ºC; McDowell, 1972) and therefore heat stress occurs (Bianca, 1962). Heat stress is one of the limiting factors in dairy production in hot climates and is hard to account for by management in the extensive grazing-based farming system of Mediterranean dairy sheep where animals are rarely kept indoors. The interest of our study was to investigate if in the Mediterranean area heat stress has an effect on dairy sheep performance. Some studies (Ames et al., 1971; Sevi et al., 2001) on sheep heat stress investigated changes in rectal temperatures, respiration rates, volumes of air inhaled and other physiological functions. Unfortunately, such measurements are costly and not feasible on a large scale in practical farming circumstances, which leads to insufficient data quantity, especially for genetic studies. In the present paper the methodology of Ravagnolo et al. (2000) based on using weather station data for Holstein cattle was pplied to Valle del Belice dairy sheep. The animals were investigated with the following aims: 1) to estimate the effects of hot weather conditions on milk production traits by using nformation from a weather station, 2) to locate the point at which heat stress starts for dairy sheep, 3) to determine a heat stress function suitable for studying genetic tolerance against heat stress, and 4) to estimate the additive genetic variances of general and heat tolerance effects on milk production traits.  aEwe milk  aHeat stress  aSheep  aBioclimatologia  aCalor  aStress  aTemperatura  aOvino leiteiro  aProdução de leite1 aVAN KAAM, J. B. C. H. M.1 aB. PORTOLANO, B.1 aMISTRAL, I.