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 < 0.001) when the THI increased from 65.62 (P1) to 83.27 (P2). Regression analyses were carried out between THI index and some parameters (HR, RR, MY, DMI, digestibility, plasma concentration of vitamin C) and between RT and same parameters (HR, RR, MY, DMI, digestibility, plasma concentration of vitamin C). Characteristics of regression analyses in the two modes were different as also were R2 and r (correlation coefficient) of the regressions. R2 in regressions on RT (R2 (RT, DMI) = 0.92 (P < 0.01); R2 (RT, MY) = 0.91 (P < 0.001)) was markedly higher relative to R2 in regressions on THI (R2 (THI, DMI) = 0.76 (P < 0.001); R2 (THI, MY) = 0.63 (P < 0.001)). The two regressions modes suggest that increasing R2 in regressions on RT confirms that rectal temperature constitutes a larger component of total variance of responses in dairy cows to hot environmental temperature.
Highlights
RT is a sensitive indicator of thermal balance and may be used to assess the negative effects of hot environments on growth, lactation and reproduction of dairy cows [1]
The present study was part of a large study aiming to detect the relationship between RT and several parameters, such as heart rates (HR), respiratory rates (RR), milk yield (MY), dry matter intake (DMI), digestibility, and plasma concentration of vitamin C under high environmental temperature
The diets fed to animals during the experiment contained, on average, 32.3% DM, 13.9% crude protein (CP), and 41.8% Neutral Detergent Fiber (NDF) on a DM basis in spring
Summary
RT (rectal temperature) is a sensitive indicator of thermal balance and may be used to assess the negative effects of hot environments on growth, lactation and reproduction of dairy cows [1]. It has been reported that body temperature is usually maintained by the thermoregulatory system within 1 ̊C of its normal under ambient conditions that do not impose severe heat stress [2]. Increased RT signifies lack of thermal balance and increased water intake to replace increased evaporative losses [6].The amplitude of the body temperature rhythm increases as ambient temperature rises [7]. Evaluation of these lag times, changes in amplitude and other features of the body temperature rhythm in response to different environmental stressors may provide an insight into how dairy cows change their thermoregulatory mechanisms during periods of heat stress [8]. The present study was part of a large study aiming to detect the relationship between RT and several parameters, such as heart rates (HR), respiratory rates (RR), milk yield (MY), dry matter intake (DMI), digestibility, and plasma concentration of vitamin C under high environmental temperature
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
