Site and extent of starch digestion of whole-plant maize silages differing in maturity stage and chop length, in dairy cows

The aims of this study were to determine the extent of starch digestion in the different digestive compartments in cows fed high whole-plant maize silage (WPMS) diets, and to evaluate the effect of maturity and chop length of WPMS on starch digestion, ruminal fermentation and milk production. The study was conducted on four dairy cows fitted with ruminal, duodenal, and ileal cannulas, in a 4 x 4 Latin square design. Dietary treatments differed in maturity stage (early vs. late) and chop length (fine vs. coarse) of WPMS. The WPMS were not processed. Diets, containing 80% WPMS, were fed at 90% of ad libitum intake level. Organic matter digestion in the different segments of the gastrointestinal tract and mean retention time of particles in the rumen and total tract, were similar between treatments. In late harvested WPMS, starch particle size distribution differed between coarse and fine chop length, and differences disappeared in rumen content. Total tract digestibility of starch was lower with late (95% of intake) than with early (99% of intake) stage. Starch ruminal digestion was high in comparison with diets containing similar proportion of starch provided by maize grain. Ruminal starch digestion was the highest with the early fine diet (95.4% of intake) and the lowest with the late coarse diet (71.3% of intake), and 70% of starch escaping ruminal digestion was digested in the small intestine. Starch digestion in hindgut was unaffected by treatments. The ruminal and total tract digestion of NDF and the ruminal pH, VFA, and ammonia concentrations were not or poorly affected by treatments. There was no difference in milk production and composition between treatments. Although differences in site of starch digestion between treatments were not statistically significant, this study suggested that the site and extent of starch digestion could be modulated by controlling maturity stage and chop length of WPMS, without affecting the energy value of the diet. (C) 2004 Elsevier B.V. All rights reserved.