Impacts of excessive energy intake and supplementation with chromium propionate on development of insulin resistance in non-lactating dairy cows

Abstract

This experiment was designed to evaluate the effects of excessive energy intake and supplementation with chromium propionate on serum concentrations of glucose, insulin, non-esterified fatty acids (NEFA), and triacylglycerol (TG), as a model to evaluate the development of insulin resistance, in non-lactating /8 Holstein x Gir cows. Thirteen multiparous, ovariectomized cows will be maintained on a single pasture with no forage available for consumption. Cows will be ranked by body weight and body condition score (BCS), and randomly allocated to three experimental groups: Group 1) MAN: diet to provide 100% of their maintenance energy requirements without chromium supplementation (n = 4), Group 2) BEPSC: diet to provide 170% of their maintenance energy requirements without chromium supplementation (n = 4), Group 3) BEPCC: diet to provide 170% of their maintenance energy requirements with chromium supplementation (n = 5; 2,5g of KemTRACE, 0,4% chromium, mixed in 97,5g of semolina/animal/day). All diets will be offered twice daily via individual self-locking head gates from day 0 to 88. Cow body weight and BCS will be assessed on days 0, 15, 38, 70, and 88 of the experiment. Blood samples will be collected prior to and 2 h after the morning feeding every 4 days, and analyzed for serum concentrations of glucose, insulin, NEFA, and TG. Glucose tolerance tests will be performed on days 32 and 88 of the experiment to determine rate of glucose disappearance and rate of insulin excretion. All variables will be analyzed using a repeated measures approach with the PROC MIXED of SAS (SAS Inst., Inc., Cary, NC), using cows as experimental unit. Treatments MAN and BEPSC will be compared to evaluate the impacts of excessive energy intake on serum concentrations of the aforementioned substances and the development of insulin resistance, whereas treatments BEPSC and BEPCC will be compared to evaluate the impact of chromium propionate supplementation on these same parameters. (AU)