Effects of high environmental temperatures on physiological and nutritional status of prepubertal Holstein heifers

摘要

A series of studies were carried out to determine the effects of increasing environmental temperature (20 to 28 to 33 degrees C) at a constant (60%) relative humidity on the physiological responses, energy and nitrogen balance of prepubertal Holstein heifers (n=4, initial body weight=198 +/- 3 kg). The relatively high environmental temperatures of 28 and 33 degrees C increased rectal temperature by 0.2 and 1.2 degrees C and increased respiration by 23 and 58 breaths per min, respectively. At 28 degrees C, dry matter intake was similar to that at 20 degrees C, whereas at 33 degrees C dry matter intake was lower (P < 0.10) by about 9%. However, the dry matter digestibility was higher (P < 0.05) at 33 degrees C than at 20 degrees C, hence the thermal treatments did not affect daily weight gain. At 33 degrees C blood urea nitrogen increased whereas hematocrit and plasma glucose concentrations decreased. At 33 degrees C energy and nitrogen intake were lower (P < 0.10), while energy and nitrogen digestibility were higher at 33 degrees C than at 20 degrees C. Urinary nitrogen was elevated at 33 degrees C resulting in lower nitrogen retention. Although, energy retention as fat did not differ (P > 0.10) among the treatments, energy retention as protein was lower (P < 0.05) at 33 degrees C than at 20 degrees C or 28 degrees C. These results confirmed that the effects of environmental temperature on prepubertal heifers were severe above 28 degrees C. (c) 2007 Elsevier B.V. All rights reserved.