Chromium supplementation and substitution of barley grain with corn: effects on metabolite and hormonal responses in periparturient dairy cows.

Summary Thirty-two multiparous Holstein cows were used to investigate the effects of chromium- l-methionine (Cr-Met) supplementation and dietary grain source on metabolic indices throughout the periparturient period. Cows were fed a total mixed ration with the concentrate portion based on ground barley (barley based diet, BBD) - or ground corn (corn-based diet, CBD) from 21 days before anticipated calving through 28 days after calving. The Cr-Met was supplemented at dosages of 0 or 0.08 mg of Cr/kg of metabolic body weight throughout the experiment. Thus, treatments were in a 2 (Cr-Met) × 2 (grain sources) factorial arrangement. Plasma glucose, non-esterified fatty acids, triglyceride, very low-density lipoprotein, blood urea nitrogen (BUN), insulin, glucagon, cortisol and insulin-like growth factor-I (IGF-I) concentrations were not affected by chromium supplementation on calving day (d 0). However, there was a trend for decreased β-hydroxybutyrate (BHBA) and increased cholesterol on d 0 in cows fed the Cr supplemented diet. On d 21 postpartum (wk 3 p.p.), plasma glucagon concentration tended to be greater in cows fed the Cr supplemented diet. However, other plasma metabolite and hormone measures were not affected by Cr supplementation in wk 3 p.p. There was no effect of grain source on d 0 plasma metabolic and endocrine measures. In wk 3 p.p., a significant difference was found only for plasma concentration of glucagon that was higher for cows fed the BBD compared with the CBD. There was an interaction of Cr-Met supplementation and grain source in wk 3 p.p. plasma concentration of BUN to decrease in CBD and increase in BBD, supplemented with Cr-Met. No Cr by grain interactions were observed for other plasma metabolic variables on d 0 and in wk 3 p.p. These results indicate that Cr-Met supplementation and substituting barley grain with corn throughout the transition period have only moderate effects on metabolic and endocrine parameters. [ABSTRACT FROM AUTHOR]