Impact of heat stress on Holstein breeding performance conducted in a semi-arid Mediterranean climate. Case of Western Algeria.

The dairy cattle husbandry systems in semi arid climate require adapting as a response to climate change. In this study, we focus on semi arid climate of Mediterranean region to assess the effect of heat stress on productive and physiological parameters of Holstein cows. The temperature-humidity index (THI), calculated as a combination of ambient temperature and relative humidity, was used to characterize heat stress. The averages of index (THI) are 71.7, 83.6 and 72.6 respectively for spring; summer and autumn. when the THI increased from average value 12 unit between spring and summer, the cows decreased their daily milk production (DMP) and dry matter intake (DMI) by 17.6 % kg/day and 22 % respectevelly. THI value was negatively correlated to DMP with regression equation DMP (kg /day) = -0,36THI+40.8 (r2 =0.72).  in semi arid condition a daily increase was observed for RT, RR an HR respectively when the THI value increased from 71.7 to 83.6 (RT 38.6˚C to 39.1˚C; RR 49.3 inspiration/min to 71.6 inspiration/min and HR 52.6beat/min to 72.7 beat/min for spring and summer respectively) with positive correlation between THI and RR, HR and RT. significant seasonal variation was detected for all physiological parameters for spring, summer and autumn period. Summer heat stress affected the physiological functions of lactating Holstein cows reared under semi arid Mediterranean climatic conditions. The Holstein breed cows are sensitive to heat stress in semi arid conditions. In the context of cow breeding practiced in conditions of semi-arid heat stress, it is necessary to find alternatives in terms of management or genetic improvement, in order to alleviate the impact of climatic stress on performance and physiological parameters.