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 moistur e corn (HMC) as energy supplement on ruminal digestion of dry matter (DM) c omponents, food intake, milk production and composition, and live weight ch ange (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 o ats and ryegrass pasture tin vitro DM digestibility: 81.0% and crude protei n: 21.3%). Six Holstein lactating cows were surgically fitted with permanen t ruminal cannula and grouped in a crossover design to study ruminal digest ion. Milk production and composition were assessed in 22 Holstein cows allo ted to T1 (n = 12) and T2 (n = 10) in a completely randomized design correc ted by covariate, using milk production and composition registered for 15 d ays 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 greater than or equal to 0.10). Ammonia N concentration was significantly lower (P less than or equal to 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 greater than or equal to 0 .10). The soluble fraction of starch was higher (P less than or equal to 0. 01) for HMC (T1: 42.53%; T2: 1.29%), and the fractional rate of starch dige stion in the rumen was also higher (P L 0.01) for HMC (T1: 9.93% h(-1); T2: 6.15% h(-1)). The ruminal digestion of neutral detergent fiber was not sig nificantly different between treatments (P greater than or equal to 0.10). Starch in feces tended (P less than or equal to 0.10) to be higher in T2 (5 14.9 g per day) than in T1 (410.0,0 per day), in agreement with higher (P l ess than or equal to 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 greater than or equal to 0.10) between treatments, althoug h T1 tended (P less than or equal to 0.10) to have a higher protein percent age (T1: 3.39%; T2: 3.30%). No significant differences in LWCs (P greater t han or equal to 0.10) were found. Higher ruminal starch digestion of HMC co uld explain the lower ruminal ammonia concentration observed in T1. Except for the tendency to produce milk with a higher protein concentration, diffe rences in rumen environment did not affect milk production and composition, (C) 2001 Elsevier Science B.V. All rights reserved.