The Effect of Top-dressing Glucose Precursores on Performance and Body Temperature Indices in Holstein Bull Calves during Heat Stress

The experiment designed to evaluate the effects of a glycerol based supplemental product on growth and dry matter intake (DMI) in Holstein bull calves during controlled heat stress (HS). Before the start of the experiment, bull calves (n= 14, 163.6 ± 30.1 kg BW) were allocated to thermal neutral conditions [26.5 ± 3.4°C] for 7 d (period 1; P1). During this period, productive parameters as well as DMI is measured as covariate for the subsequent HS period. Following P1, a cyclical HS pattern was implemented for 21 d (P2) where daily ambient temperatures ranged from 29.1 to 39.7°C. During P2, half of the HS calves (n=7) received a control diet (CON) and the other half received the control diet supplemented with a product containing gluconeogenic precursors (GLU, 300 g/d)). Throughout each period feed and water intake were measured daily and respiration rate and rectal temperature were recorded at 0600, 1100 and 1500 h daily. The diet had no effect on DMI. Although HS markedly reduced growth as expected, supplemental GLU did not affect body weight gain. Supplemental GLU decreased respiratory rate at 1500 h (P