Effects of dietary starch source and buffers on milk responses and rumen fatty acid biohydrogenation in dairy cows fed maize silage-based diets

Effects of dietary starch source and buffers on milk responses and rumen fatty acid biohydrogenation of dairy cows fed maize silage-based diets were evaluated using 16 Holstein cows in an incomplete 4 × 4 Latin Square-design experiment with three periods. Each experimental period lasted for 3 weeks. The diets fed as a total mixed ration consisted (dry matter basis) of 450 g/kg maize silage, 50 g/kg coarsely chopped wheat straw and 500 g/kg concentrate. The four dietary treatments were formulated to be isonitrogenous, iso-starch, and to differ in the main starch source in the concentrate and the addition of buffers and neutralizing substances (B: sodium bicarbonate and magnesium oxide). Diets were formulated with concentrates based on wheat with (WB) or without B (W), or with concentrates based on maize with (MB) or without B (M). Dietary treatments did not affect dry matter intake, and maize-based concentrates tended to increase milk production—probably due to the different profile of end products of digestion. Addition of buffers did not affect productive responses. Dietary treatments had only small effect on most milk fatty acids. Maize diets induced lower 16:0, 16:1 cis-9 and odd-chain fatty acids (13:0, 15:0, 17:0 and 17:1 cis-9) and higher total C18 fatty acids than wheat diets. Results did not confirm the anticipated effect of rate of ruminal starch degradation on milk 18:1 trans-10. Dietary buffers led to more complete rumen biohydrogenation, with a decrease in almost all biohydrogenation intermediates, including rumenic acid. Explanations for effects of dietary buffers on rumen biohydrogenation pattern are needed.