Abstract

SARAVIA, Celmira; ASTIGARRAGA, Laura; VAN LIER, Elize  and  BENTANCUR, Oscar. Impact of Heat Waves on Dairy Cows in Salto (Uruguay). Agrociencia Uruguay [online]. 2011, vol.15, n.1, pp.93-102. ISSN 1510-0839.

The aim of this study was to characterise summer meteorological determining factors (MDF) of different severity in Salto (Uruguay) and their impact on the physiological and productive responses of dairy cows. The MDF were characterised according to the mean temperature-humidity index (THI), average hours per day with THI ³72 and minimum and maximum daily temperatures. Rectal temperature (RT) and respiratory frequency (RF) of the cows were taken at 6:00 and 15:00 h, and the time spent grazing (GT) during daytime. One severe heat wave (SHW), three light heat waves (LHW) and days of no heat wave (NHW) were identified. The MDF affected RT and RF of the cows (P<0,0001). The RF and RT (6:00 and 15:00) were higher in SHW compared to LHW and NHW (P<0,0001). Grazing time was less during SHW compared to LHW and NHW (P<0,0001). The production of milk, fat and protein were lower during SHW (P<0,0001) than during LHW and NHW. Somatic cell count was lower during SHW than LHW but not NHW (P=0,0618). During SHW cows did not maintain normothermia and spent less time grazing, reducing productivity. During LHW cows recovered normothermia during the night, with no reduction in productivity compared to NHW.

Keywords : heat stress; rectal temperature; respiratory frequency; grazing time; milk production and composition.

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