| The objectives of this dissertation were A) to evaluate the lactation performance of cows fed brown midrib (BMR) corn silage, normal (NML) corn silage, and their mixture (MIX) that was harvested at two differing stages of maturity (36 and 42% DM), and B) the effect of feeding 35% (DM basis) NML corn silage (NML-LOW), 35% BMR corn silage (BMR-LOW), and 50% BMR corn silage ( BMR-HIGH) in a total mix ration (TMR) on dry matter intake (DMI), nutrient digestibility, and performance of high yielding early lactating dairy cows. When forages were harvested at a mature stage (42% DM), DMI was higher in cows fed BMR than those in NML and intermediate for cows fed MIX. Unexpectedly, yield of milk, 3.5% fat-corrected milk ( FCM) and energy-corrected milk (ECM) was similar among treatments. Because of higher DMI but similar yield of FCM, cows fed BMR corn silage tended to have a lower feed efficiency (FCM/DMI) than cows fed the other treatments. When forages were harvested at an ideal stage of maturity (36% DM), cows fed with BMR and MIX resulted in lower DMI compared to those fed NML corn silage. Despite having lower DMI, the cows fed BMR and MIX supported similar yield of milk, FCM, and ECM. Due to lower intake but similar productive performance, the cows fed BMR and MIX corn silage had higher feed efficiency than cows fed with NML corn silage. Cows fed BMR-HIGH and BMR-LOW resulted in higher yield of milk and ECM than cows fed NML-LOW but DMI was similar among treatments. The yield of FCM was higher in cows fed BMR-LOW than NML-LOW but similar to those in BMR-HIGH treatment. The apparent total tract digestibility of feed DM, organic matter, starch, crude protein, and neutral detergent fiber (NDF) was lower in cows fed NML-LOW compared to the other treatments. Results of this dissertation showed that feeding cows with BMR corn silage was beneficial in two of three lactation trials (increasing feed efficiency in one and increasing milk production in another) and thus, offer a great potential for dairymen to improve their net farm income. |
