Effects of varying the degree of synchrony of energy and nitrogen release in the rumen on the synthesis of microbial protein in lactating dairy cows consuming a diet of grass silage and a cereal-based concentrate

The object of the experiment was to test the hypothesis that altering the d egree of synchrony in the ruminal release of available energy and nitrogen would affect microbial protein synthesis (MPS) when the diet contained a hi gh proportion of readily fermentable carbohydrate. Four lactating dairy cow s were given a basal diet of (kg DM. day(-1)) 8.0 grass silage, 4.2 barley and 1.8 groundnut meal containing 31.4g N kg(-1) DM. The experiment was des igned as a 4 x 4 Latin square with periods lasting 14 days. The treatments were (1) the basal diet given in two equal meals at 10:00 and 22:00h (BASAL ), supplemented with (2) 2.0kg maltodextrin given as a continous intrarumin al infusion (CONT), (3) 2.0 kg maltodextrin as two 6-h infusions starting a t 10:00 and 22:00 h (SYNC) and (4) 2.0 kg maltodextrin given as two 6-h inf usions starting at 16:00 and 04:00h (ASYNC). All three infusion treatments reduced (P < 0.05) the concentration of ruminal ammonia relative to BASAL b ut only the CONT and SYNC treatments increased (P < 0.05) MPS over the leve l with BASAL; the value for ASYNC was the same as that for BASAL. Lactic ac id was a minor product of the ruminal fermentation with all treatments. All three infusions reduced (P < 0.05) the plasma concentration of urea and th e urinary output of nitrogen but there were no differences among the infusi on treatments. It is concluded that with this diet, containing about 30% of DM as fermentable carbohydrate, altering the degree of synchrony in the ra tes of ruminal release of energy and nitrogen had a marked effect on MPS. ( C) 1999 Society of Chemical Industry.