Chromium improves production and alters metabolism of early lactation cows in summer.

Metabolic demands of early lactation introduce enormous challenges to dairy cows when coincided with environmental stresses. The objective of this study was to determine effects of a chromium (Cr) supplement on feed intake and blood indicators of nutrient metabolism in early lactation cows in summer. Fifteen Holstein cows at 38±6 days in milk were grouped based on parity and randomly assigned to three supplemental doses of 0, 0.05 and 0.10 mg Cr/kg of BW(0.75) . Cows received a basal mixed ration with a forage to concentrate ratio of 57.7:42.3, twice daily at 09:00 and 16:00 h for 9 weeks. The first 2 weeks were for adaptation, and the following 7 weeks were for weekly sampling and data collection. The Cr supplement (a Cr-methionine product with 10% Cr and 90% Met from a compound containing one atom of Cr and three molecules of Met) was mixed with 100 g of ground corn and top dressed with the morning feed. The average ambient temperature-humidity index was 77.7 units during the study. Dry matter intake increased from 21.8 to 24.2 and 23.7 kg/day when 0.05 and 0.10 mg Cr/kg BW(0.75) was provided respectively. Milk output of energy, fat, protein and total solids increased by providing Cr at 0.05 mg but not 0.10 mg/kg BW(0.75) . Both doses of Cr increased milk protein content, but the higher Cr dose reduced feed efficiency compared with control. While rectal temperature and body condition score were unaffected, cows receiving 0.05 mg and not 0.10 mg Cr/kg BW(0.75) tended to have greater respiration rate than control cows. Blood insulin and non-esterified fatty acids concentrations and the insulin to glucagon ratio decreased, and serum albumin increased when cows received 0.05 mg of Cr/kg BW(0.75) . Blood glucose, glucagon, insulin-like growth factor-1, total protein, globulins, urea, BHBA, triglycerides, cholesterol, cortisol, progesterone, and high- and very low-density lipoproteins were not affected. Therefore, supplemental Cr supply at 0.05 and 0.10 mg/kg BW(0.75) improved feed intake, only at 0.05 mg/kg BW(0.75) increased milk secretion, and mainly at 0.05 mg/kg BW(0.75) altered peripheral nutrient metabolism in early lactation Holstein cows under high ambient temperatures.