Milk production and ruminal digestion in lactating dairy cows grazing temperate pastures and supplemented with dry cracked corn or high moisture corn

We studied the effects of dry cracked corn (DC) replacement by high moisture corn (HMC) as energy supplement on ruminal digestion of dry matter (DM) components, food intake, milk production and composition, and live weight change (LWC) in lactating dairy cows grazing pastures. Treatments were: T1, 9.0 kg of HMC (74% DM) and T2, 6.8 kg of DC (85.9% DM). Cows grazed winter oats and ryegrass pasture (in vitro DM digestibility: 81.0% and crude protein: 21.3%). Six Holstein lactating cows were surgically fitted with permanent ruminal cannula and grouped in a crossover design to study ruminal digestion. Milk production and composition were assessed in 22 Holstein cows alloted to T1 (n=12) and T2 (n=10) in a completely randomized design corrected by covariate, using milk production and composition registered for 15 days prior to starting the experiment. Eight cows per treatment were used to estimate the total intake. Total dry matter intake and forage intake were not different between treatments (P≥0.10). Ammonia N concentration was significantly lower (P≤0.01) in T1 (12.87 mg dl−1) than in T2 (19.09 mg dl−1); however, ruminal pH and total volatile fatty acids were not different (P≥0.10). The soluble fraction of starch was higher (P≤0.01) for HMC (T1: 42.53%; T2: 1.29%), and the fractional rate of starch digestion in the rumen was also higher (P≤0.01) for HMC (T1: 9.93% h−1; T2: 6.15% h−1). The ruminal digestion of neutral detergent fiber was not significantly different between treatments (P≥0.10). Starch in feces tended (P≤0.10) to be higher in T2 (514.9 g per day) than in T1 (410.0 g per day), in agreement with higher (P≤0.05) starch digestibility in the total tract of high moisture corn (T1: 90.26%; T2: 86.87). Milk production and composition was not different (P≥0.10) between treatments, although T1 tended (P≤0.10) to have a higher protein percentage (T1: 3.39%; T2: 3.30%). No significant differences in LWCs (P≥0.10) were found. Higher ruminal starch digestion of HMC could explain the lower ruminal ammonia concentration observed in T1. Except for the tendency to produce milk with a higher protein concentration, differences in rumen environment did not affect milk production and composition.