Lactation performance, in situ degradability, and rumen fermentation of Holstein cows fed BMR-6 sorghum silage versus corn silage based diets

The objectives of the study were to determine 1) the lactation performance, in situ degradability, and rumen fermentation of Holstein cows fed a bmr-6 sorghum silage (SS) vs. a leading non-bmr corn silage (CS) variety and 2) degradation kinetics of DM and starch from sorghum grain isolated from SS. In Experiment 1, four second lactation Holstein cows (578 ± 41 kg BW) in mid lactation, 101 to 113 DIM, were randomly assigned to diets containing SS or CS in a 2 × 2 crossover design with 14-d adaptation periods followed by 7-d collection periods. Cows were individually housed in open corrals (3.3 by 10 m) and fed once daily at 1000 h. Diets were formulated to supply 28% of the DM as each silage. Additionally, the diets were formulated to supply similar concentrations of NDF and total tract digestible starch, assuming 50% starch digestibility for SS. This was accomplished by replacing a portion of the steam-flaked corn (8% of diet DM) in the SS diet with 4% each of soy hull pellets and cottonseed hulls in the CS diet. All other dietary ingredients were similar between treatments. Milk production (32.6 vs. 31.4 ± 5.7 kg/d; P > 0.725) and percentages and yields of milk components did not differ (P ≥ 0.246). In situ degradability of CS and SS were determined at 0, 6, 12, 18, 24, 36, 48, and 72 h. Cows fed CS had greater (P ≤ 0.001) DM, OM, and NDF disappearances compared with cows fed SS at all incubation times. There was a treatment × time interaction (P = 0.004) for rumen pH recorded with greater pH at 1, 2, 3, 11, 12, 17, 23, and 24 h relative to feeding for SS. Total gas and methane produced from samples taken 3 h after feeding were greater (P ≤ 0.002) for SS than for CS. The grain portion of SS was manually separated and ruminally incubated for 0, 3, 6, 12, 18, 24, 36, 48, and 72 h during Experiment 2. There were no differences (P > 0.315) between DM and starch disappearances of the sorghum grain until 18 h (P ≤ 0.001). The DM disappearance continued to increase up to 72 h, but maximum starch disappearance, 55.7%, was reached at 18 h. Sorghum silage is an energy forage that may be used in lactating cow rations in areas where water availability may limit corn silage production; however, NDF and starch degradation should be improved.