Interaction of potassium carbonate and soybean oil supplementation on performance of early-lactation dairy cows fed a high-concentrate diet.

Potassium carbonate supplementation is known to improve milk fat synthesis and to modify milk mineral composition in dairy cows. The objective of the current experiment was to evaluate the effect of KCO on production performance, biohydrogenation of fatty acids (FA), and mineral composition of milk in early-lactation dairy cows fed a high-concentrate diet with or without soybean oil (SBO), as a source of polyunsaturated FA. Twenty-eight ruminally fistulated Holstein cows were used in a randomized complete block design. The experiment lasted 33 d, including a 5-d pretreatment collection period used as a covariate. Experimental treatments were arranged as a 2 × 2 factorial with 0 or 1.5% KCO and with 0 or 2% SBO, and balanced to contain 40% forage (57% corn silage + 43% grass silage) and 60% concentrate. Preplanned orthogonal contrasts were used to assess the effects of KCO, SBO, and their interaction. Feeding KCO did not affect milk yield, but tended to increase 4% fat-corrected milk and fat yield when combined with SBO. However, adding SBO to diets increased milk yield. Dietary KCO supplementation did not affect milk fat concentration of trans-10 18:1 or any other identified biohydrogenation intermediates. Soybean oil supplementation decreased milk fat concentration of C16 and de novo synthesized FA, and increased preformed FA. Among the other effects of SBO supplementation observed, concentrations of cis-9,trans-11 18:2 increased, as well as most of the cis and trans isomers of 18:1 and 18:0. Milk urea N decreased in cows fed KCO as compared with unsupplemented diets. A positive relation was established between milk Cl concentration and milk yield, suggesting that the equilibrium of this ion is linked to the efficiency of lactogenesis. The effect of KCO on this mineral equilibrium in the mammary gland remains to be established. Overall, results have shown that potential effect of KCO on milk fat synthesis is dependent on the levels of dietary polyunsaturated FA.