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A normal corn silage hybrid (Mycogen FQ7511) was cut at a normal height (leaving 10-15 cm of stalk) or a high height (leaving 46-51 cm of stalk) and a BMR hybrid (F2F797) was harvested at a normal-cut height (leaving 10-15 cm of stalk). High cutting of FQ7511 increased the concentrations of DM (+4%), CP (+5%), NEL (+3%) and starch (+7%) but decreased the concentrations of ADF (-9%), NDF (-8%) and ADL (-13%) compared to normal-cut FQ7511. The 30 h NDF-D of normal-cut FQ7511, high-cut FQ7511 and normal-cut BMR corn silage was 51.7, 51.4, and 63.5%, respectively. Corn silages were fed to cows and comprised 45% of the TMR ration DM. Diets were isonitrogenous and isocaloric. Thirty Holstein cows (average 81 ± 48 DIM) were blocked by production and DIM and randomly assigned to ten simultaneous 3 × 3 Latin squares. Each period consisted of a 3-wk period and the data from last 10 d of each period was used for statistical analysis. Mean separation was performed using the Least Significant Difference procedure when the treatment effect was significant. Milk production, milk protein production and milk lactose % were greater (P < 0.05) for cows fed normal-cut BMR (48.8 kg/d, 1.40 kg/d, 4.88%) than for those fed normal-cut FQ7511 (46.8 kg/d, 1.34 kg/d, 4.82%) or high cut 7511 (47.7 kg/d, 1.36 kg/d, 4.83%). Cows fed high-cut FQ7511 had milk with less fat (3.48%) than cows fed high-cut silage (3.60%). Cows fed BMR corn silage tended to produce more (P < 0.12) 3.5% FCM than cows fed the other silages. Dry matter intake was not affected by treatment. Feed efficiency (kg of 3.5% FCM milk/kg of DMI) was greater (1.83, P < 0.05) for cows fed normal-cut BMR than those fed normal-cut 7511 (1.77) or high cut 7511 (1.75) corn silages. Cows fed normal-cut BMR had milk with a lower (P < 0.05) MUN (14.8 mg/dl) than did other treatments (average of 16.2 ml/dl). Harvesting a normal corn hybrid at a high-cut height improved its nutritive value but the improvement in feeding value to lactating cows was not equivalent to that found when cows were fed BMR corn silage harvested at a normal-cut height. [ABSTRACT FROM AUTHOR]

A brown midrib (BMR) hybrid and a silage-specific non-BMR (7511FQ) hybrid were harvested at a normal cut height leaving 10 to 15 cm of stalk in the field. The non-BMR hybrid was also cut at a greater height leaving 45 to 50 cm of stalk. Cutting high increased the concentrations of dry matter (+4%), crude protein (+5%), net energy for lactation (+3%), and starch (+7%), but decreased the concentrations of acid detergent fiber (-9%), neutral detergent fiber (-8%), and acid detergent lignin (-13%) for 7511FQ. As expected, the BMR corn silage was 30% lower in lignin concentration than 7511FQ. After 30 h of in vitro ruminal fermentation, the digestibility of neutral detergent fiber for normal cut 7511FQ, the same hybrid cut high, and the normal cut BMR hybrid were 51.7, 51.4, and 63.5%, respectively. Twenty-seven multiparous lactating cows were fed a total mixed ration composed of the respective silages (45% of dry matter) with alfalfa haylage (5%), alfalfa hay (5%), and concentrate (45%) (to make the TMR isocaloric and isonitrogenous) in a study with a 3 x 3 Latin square design with 21-d periods. Milk production was greater for cows fed the BMR hybrid (48.8 kg/d) compared with those fed the normal cut 7511FQ (46.8 kg/d) or cut high (47.7 kg/d). Dry matter intake was not affected by treatment. Feed efficiency for cows fed the BMR silage (1.83) was greater than for those fed high-cut 7511FQ (1.75), but was not different from cows fed the normal cut 7511FQ (1.77). Cows fed the BMR silage had milk with greater concentrations of lactose but lower milk urea nitrogen than cows on other treatments. Harvesting a silage-specific, non-BMR corn hybrid at a high harvest height improved its nutritive content, but the improvement in feeding value was not equivalent to that found when cows were fed BMR corn silage. [ABSTRACT FROM AUTHOR]