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.