Effects of Reduced Starch Diets and Starch Digestibility on Nutrient Digestibility, Microbial Protein Flow, and Lactation Performance of Dairy Cows.

摘要

A meta-analysis, two animal experiments, and one data mining experiment were conducted to determine the effects of feeding reduced-starch (RS) diets and starch digestibility on dairy cattle performance.;A meta-analysis was conducted to determine the effects of feeding RS diets on intake, lactation performance, and ruminal parameters. Dietary starch was reduced by partial replacement of grain with non-forage fiber sources or forages. Dry matter intake, milk, fat, and protein yield were decreased as dietary starch was reduced. Total ruminal volatile fatty acid concentration was decreased as dietary starch was reduced. Molar proportion of ruminal acetate was increased as dietary starch was reduced. Reducing dietary starch decreased lactation performance of dairy cows.;The first animal experiment determined the effects of normal or RS diets and finely- or coarsely-ground corn on performance of lactating dairy cows. Milk and protein yields were reduced for cows fed RS diets, however, fat-corrected milk was increased for cows fed the normal-starch finely-ground corn and RS coarsely-ground corn diets. Ruminal digestibility of NDF was increased for cows fed the RS diets. Total tract digestibility of NDF was greater on the RS diets, while total tract starch digestibility was greater on the RS diets and the finely-ground corn diets. Cows fed the finely ground corn diets had greater ruminal propionate and lower rumen pH.;The second animal experiment determined the effects of feeding RS diets by partially replacing corn grain with soyhulls (SH) or corn silage (CS), or CS and grain with SH. Partial replacement of corn grain with SH or CS increased milk fat content compared with partial replacement of CS and corn grain with SH. Partial replacement of corn grain with SH or CS increased total tract NDF and starch digestion. Diet digestibility and performance of mid-lactation cows fed RS diets by partially replacing corn grain with SH or CS was similar to or improved compared to cows fed a normal-starch diet.;The third experiment tested whether total tract starch digestibility can be predicted from the concentration of starch in fecal dry matter. Total tract starch digestibility was predicted accurately from fecal starch concentration.