Thermoregulatory responses of Saanen goats fed increasing levels of sugarcane in place of corn silage

Abstract

The present study evaluates the thermoregulatory responses of goats fed with sugarcane (Saccharum officinarum L.) in place of corn (Zea mays L.) silage. Twelve Saanen goats with average body weight (BW) of 45.22 ± 5.3 kg and 42.23 ± 2.66 days of lactation were distributed in Latin square, 4 × 4. The experiment was divided into four intervals of 21 days each, with 14 days of adaptation to the experimental diets and 7 for data recording. Four levels of sugarcane (0%, 33%, 66%, and 100%) were used, in isoprotein diets formulated in the proportion of 50:50 (roughage:concentrate), based on corn (Zea mays L.) and soybean (Glycine max L.) meal. Meteorological data and bioclimatic indices were used to monitor the thermal environment of the animals. Thermoregulatory responses were evaluated in each period, with measurements of the physiological variables, rectal temperature (RT, ºC), heart rate (HR, beat/min), respiratory rate (RR, mpm) and skin temperature (ST, ºC), every two days, and sweating rate (SR, g/m²/h) only once. No differences (P > 0.05) were observed in the diet with sugarcane for ST, RR, SR and BW (kg), but the effect was significant (P < 0.01) for RT and HR. Nevertheless, even at the highest level of replacement, RT did not exceed the normal physiological levels of the animals. However, the observed values of HR and RR indicate the occurrence of heat stress throughout the experiment. Tachypnea and tachycardia occurred at significantly higher levels in the afternoon compared to the morning, suggesting that the animals activated thermoregulatory mechanisms to dissipate heat at the hottest times of the day. It was concluded that lactating Saanen goats, with production of up to 2.03 kg/day of milk, have their thermoregulatory responses (RT and HR) partially influenced by sugarcane, in replacement of corn silage in the diet.