IMPACT OF NONFIBER CARBOHYDRATE ON INTAKE, DIGESTION, AND MILK-PRODUCTION BY DAIRY-COWS

Four concentrations of dietary nonfiber carbohydrate (42, 36, 30, and 24%) were evaluated using eight multiparous Holstein cows (662 kg of B W; 63 DIM) in replicated 4 x 4 Latin squares with 28-d periods. Shelle d com and soybean meal were partially replaced with wheat middlings, d ried brewers grains, and soy hulls to formulate 36, 30, and 24% nonfib er carbohydrate diets. Decreasing dietary nonfiber carbohydrate decrea sed DMI, did not affect actual or fat-corrected milk production, incre ased milk fat percentage, and decreased milk protein percentage and pr oduction. Apparent total tract DM and OM digestibilities were highest for 36% and lowest for 24% nonfiber carbohydrate diets. Digestibility of NDF was lowest for die 42% nonfiber carbohydrate diet. Ruminal pH a nd acetate:propionate increased, and total VFA concentrations decrease d, as dietary nonfiber carbohydrate decreased. Ruminal degradation of alfalfa hay DM and NDF were higher for low nonfiber carbohydrate diets . Significant depression of DMI (.9 to 1.8 kg/d) coincided with dietar y nonfiber carbohydrate concentration at or below 30%. Results indicat e that diets for cows producing 40 kg/d should contain more than 30% n onfiber carbohydrate and suggest little benefit of 42 over 36% nonfibe r carbo-diets.