Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 2000
Publication Date: April 1, 2001
Interpretive Summary: Corn varieties containing the mutant brown midrib gene (bm3) have lower lignin content, and as a result, exhibit a greater digestibility of the fiber fraction. Because, predicted energy values are largely based on the fiber content of forges and do not consider decreased lignification, the energetic value of bm3 corn silage is severely underestimated. Thus, the objectives of this experiment were to determine the effects of feeding bm3 corn silage on energy balance in lactating and non-lactating dairy cows. The result of this study showed that the increase in milk production observed with feeding bm3 corn silage is a function of increased dry matter intake rather than improved efficiency of converting feed energy to milk energy. Inclusion of bm3 in the ration of non-lactating cows at maintenance energy intake increased dry matter and organic digestibility and the efficiency of conversion of feed energy to energy available for metabolism compared with cows fed rations containing typical corn silage. Nevertheless, calculated net energy for lactation values were similar for bm3 corn silage and typical corn.
Effects of genotype and level of intake on net energy for lactation values of corn silage were evaluated by indirect calorimetry in lactating and dry, nonpregnant dairy cows. Six multiparous Holstein cows in early lactation were fed diets containing either brown midrib (bm3) or isogenic normal corn silage. Dietary treatments were isogenic and bm3 diets fed ad libitum, and bm3 diet restricted-fed. Dry matter intake was 2.4 kg/d greater for cows fed the bm3 diet ad libitum compared with cows fed the isogenic diet. Apparent digestibilities of dry matter (DM), organic matter, neutral detergent fiber, and acid detergent fiber were greater for cows restricted-fed bm3 than the isogenic diet. In Experiment 2, six dry, nonpregnant Holstein cows were fed maintenance diets containing either bm3 or isogenic corn silage. Apparent digestibilities of DM, organic matter, neutral detergent fiber, and acid detergent fiber were greater for cows fed bm3 compared to isogenic corn silage. Digestible energy and metabolizable energy were greater for maintenance diets containing bm3 compared with isogenic corn silage, respectively. These data indicate increased milk production observed with feeding bm3 is a function of increased DM intake rather than an increase in energetic efficiency. Increased organic matter digestibility of bm3 corn silage resulted in greater intakes of digestible energy and metabolizable energy values in cows fed at maintenance levels of intake. However, calculated net energy for lactation values of bm3 and isogenic corn silages were similar at both productive and maintenance levels of feeding.