Effect of alfalfa silage storage structure and roasting corn on production and ruminal metabolism of lactating dairy cows.

The objective of this study was to determine if feeding roasted corn would improve production and nutrient utilization when supplemented to lactating cows fed 1 of 3 different alfalfa silages (AS). Forty-two lactating Holstein cows (6 fitted with ruminal cannulas) averaging 77 d in milk and 43 kg of milk/d pretrial were assigned to 2 cyclic changeover designs. Treatments were AS ensiled in bag, bunker, or O2-limiting tower silos and supplemented with ground shelled corn (GSC) or roasted GSC (RGSC). Silages were prepared from second-cutting alfalfa, field-wilted an average of 24 h, and ensiled over 2 d. Production and N utilization were evaluated in 36 cows during four 28-d periods, and ruminal fermentation was evaluated with 6 cows during five 21-d periods. Experimental diets contained 40% AS, 15% corn silage, and 35% of either GSC or RGSC on a dry matter basis. No significant interactions between AS and corn sources were detected for any production trait. Although the chemical composition of the 3 AS was similar, feeding AS from the O2-limited tower silo elicited positive production responses. Yields of 3.5% fat-corrected milk and fat were increased 1.7 kg/ d and 150 g/d, and milk fat content was increased 0.3% when cows were fed diets based on AS from the O2-limiting silo compared with the other 2 silages. The responses in milk fat were paralleled by an average increase in acid detergent fiber digestibility of 270 g/d for cows fed AS from the O2-limiting tower silo. However, ruminal concentrations of lipogenic volatile fatty acids were unchanged with AS source. Cows fed RGSC consumed 0.6 kg/d more dry matter and yielded 30 g/ d more protein and 50 g/d more lactose than cows fed GSC diets. There was no evidence of increased total tract digestibility of organic matter or starch, or reduced ruminal NH(3) concentration, when feeding RGSC. Free amino acids increased, and isovalerate decreased in rumen fluid from cows fed RGSC diets. However, responses in production with roasted corn were mainly due to increased dry matter intake, which increased the supply of energy and nutrients available for synthesis of milk and milk components.