A Complex Interrelationship between Rectal Temperature and Dairy Cows’ Performance under Heat Stress Conditions

Abstract

Upper limit of thermal stability and subsequent rise of thermoregulatory functions are affected by body temperature. This study was designed to determine the effects of rectal temperature (RT) on dairy cows’ performance (heart rates (HR), respiratory rates (RR), milk yield (MY), dry matter intake (DMI), digestibility, plasma concentration of vitamin C under hot climate. This study was carried out in 2009, in north-west of Tunisia using 30 Holstein cows in mid lactation. The experiment was performed in spring (15th of February-15th of March: P1) and summer (1st-30th of August: P2). On each test day, temperature-humidity index (THI), RT, HR, RR, MY, DMI, digestibility and plasma VC concentration were determined. All this parameters were affected (P 2 and r (correlation coefficient) of the regressions. R2 in regressions on RT (R2 (RT, DMI) = 0.92 (P 2 (RT, MY) = 0.91 (P 2 in regressions on THI (R2 (THI, DMI) = 0.76 (P 2 (THI, MY) = 0.63 (P 2 in regressions on RT confirms that rectal temperature constitutes a larger component of total variance of responses in dairy cows to hot environmental temperature.