Abstract #73

# 73
Effects of a brown midrib corn silage hybrid with enhanced starch digestibility on production and nutrient digestibility in lactating dairy cows.
Alexander Tebbe*1, William Weiss1, 1Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH.

Feeding corn silage hybrids selected for high fiber digestibility can increase energy intake and milk production, but these hybrids often have reduced starch digestibility. A hybrid with enhanced fiber and starch characteristics may improve feed efficiency. The objective was to determine the nutritional value of corn silage from a brown midrib (bm3) hybrid selected for floury endosperm (bm3-Plus; Unified, Dow AgroSciences, Indianapolis, IN) compared with an isogenic bm3 and a conventional dual-purpose (DP) hybrid. Twenty-one Holstein cows averaging 105 DIM were used in 7 replicated 3 × 3 Latin squares with 28 d periods. Two of the 7 squares were used to measure nutrient digestibility via total collection of urine and feces. Cows were blocked by parity and randomly assigned to 1 of 3 diets formulated to contain similar concentrations of corn silage (46% of DM) and nutrients (34.3% NDF, 23.2% starch, and 17.0% CP) but contain different corn silage hybrids: (1) DP (38.6% NDF, 36.9% starch), (2) bm3 (40.2% NDF, 29.9% starch), and (3) bm3-Plus (41.0% NDF, 29.8% starch). Based on in vitro digestibility, the bm3 hybrids had less digestible starch (3 h incubation) and higher NDF digestibility compared with DP; however, between bm3 hybrids, in vitro starch digestibility was similar. Hybrid did not affect DMI (average 25.7 kg/d; P > 0.10) or in vivo NDF digestibility (average 51.5%; P > 0.10). Feeding bm3-Plus increased (P < 0.09) yields of milk and milk energy about 2 kg/d and 1.6 Mcal/d, respectively, compared with DP and bm3 hybrids. The bm3-Plus diet increased (P < 0.01) feed efficiency nearly 6% compared with bm3 and DP (milk energy/DMI; 1.10 vs 1.04 Mcal/kg) likely from greater (P < 0.04) total-tract starch digestibility (88.3 vs 85.0%). Compared with standard bm3, cows consuming bm3-Plus had less biohydrogenation intermediates in milk fat and greater milk fat content (3.1 vs 2.9%; P < 0.04) indicating potentially better rumen conditions. Feeding silages with both enhanced fiber and starch digestibility had improved nutritional value compared with a conventional hybrid or a hybrid selected for greater fiber digestibility.

Key Words: corn silage hybrids, digestibility, brown midrib