Effects of brown midrib corn silage on the energy balance of dairy cattle

Effects of genotype and level of intake on net energy for lactation values of corn silage were evaluated by indirect calorimetry in two experiments us ing lactating and dry, nonpregnant dairy cows. In experiment 1, six multipa rous Holstein cows in early lactation were fed experimental diets containin g either brown midrib (bm3) or isogenic normal corn silage. Dietary treatme nts were isogenic and bm3 diets fed ad libitum, and the bm3 diets restricte d-fed. Dry matter (DM) intake was 2.4 kg/d greater for cows fed the bm3 die t ad libitum compared with cows fed the isogenic diet. Apparent digestibili ties of DM, organic matter, neutral detergent fiber, and acid detergent fib er were greater for cows restricted-fed bm3 than the isogenic diet. In expe riment 2, six dry, nonpregnant Holstein cows were fed maintenance diets con taining either bm3 or isogenic corn silage. Apparent digestibilities of DM, organic matter, neutral detergent fiber, and acid detergent fiber were gre ater for cows fed bm3 compared with isogenic corn silage. Digestible energy and metabolizable energy were greater for maintenance diets containing bm3 compared with isogenic corn silage, respectively. These data indicate incr eased milk production seen in other studies is a result of increased DMI ra ther than an increase in energy efficiency. Increased organic matter digest ibility of bm3 corn silage resulted in greater digestible energy and metabo lizable energy values in cows fed at maintenance energy intake. However, ca lculated net energy for lactation values of bm3 and isogenic corn silages w ere similar at both productive and maintenance levels of feeding.