Effects of chromium supplementation on weight gain, feeding behaviour, health and metabolic criteria of environmentally heat-loaded Holstein dairy calves from birth to weaning.

The objectives of this study were to investigate the effects of chromium (Cr) supplementation on feed intake and meal pattern, weight gain and skeletal growth, and health and metabolic criteria of environmentally heat-loaded dairy calves during the pre-weaning period. Forty-eight newborn female calves were allotted randomly to a control group (no Cr supplement; Cr-) or a Cr group (Cr+) receiving 0.05 mg Cr (as Cr-methionine)/kg BW0.75 . Cr was provided in the liquid feed (colostrum and milk) during the pre-weaning period. The average maximum temperature-humidity index was 83.7 U, indicating severe environmental heat load. Despite reduced meal frequency and increased in inter-meal interval, Cr supplementation tended to increase starter feed intake and total dry matter intake as a result of increased meal size and duration. Respiration rate was lower in Cr+ calves. Calf growth, rectal temperature, faecal score and incidence of diarrhoea or pneumonia were not affected by Cr supplementation, but number of days with diarrhoea and treatment duration decreased during the pre-weaning period. Cr supplementation tended to increase resting time and decreased time devoted to non-nutritive oral behaviours. At weaning, serum concentration of glucose was lower but total protein and globulin concentrations were higher in Cr+ calves. In Cr+ calves, the activity of glutathione peroxidase was higher and lower on d 49 and 63 of the study, respectively, compared to the control calves. Activity of catalase was increased on d 21 and tended to decrease on d 35 in Cr+ calves. In general, Cr supplementation to environmentally heat-loaded dairy calves decreased non-nutritive oral behaviours, improved feed intake and decreased days with diarrhoea and treatment duration, but had minimal effects on weight gain, metabolism and indicators of oxidative stress or insulin function.