Effect of brachytic2 mutation in corn silage on performance, apparent total-tract digestibility, and greenhouse gas emissions of lactating Holsteins fed 2 concentrations of dietary neutral detergent fiber.

Corn hybrids carrying the brachytic2 (br2) mutation have reduced plant height and improved plant standability. The objective of this study was to evaluate the effect of feeding corn silage (CS) from br2 corn with CS from conventional tall corn on feed intake, productivity, total-tract nutrient digestibility, and greenhouse gas emissions of Holstein cows fed diets with high or low dietary NDF. Twenty primiparous and 20 multiparous Holstein cows (76 ± 31 DIM, 46 ± 9.0 kg milk/d, 658 ± 83 kg BW) were enrolled in a randomized complete block design with a 14-d pretreatment period in which all cows were fed a common diet and a 42-d period in which cows were fed 1 of 4 diets. Experimental diets contained br2 or tall CS at 2 dietary NDF contents (25% and 30%). Low-NDF diets had 17% CP, 32% starch, and 17% forage NDF (forNDF); high-NDF diets had 18% CP, 23% starch, and 24% forNDF. Data were analyzed using PROC GLIMMIX of SAS 9.4. Contrasts were used to determine the effect of CS hybrid, the effect of NDF content, and their respective interaction. Cows fed br2 CS had greater DMI (27.5 vs. 26.5 kg), ECM (44.6 vs. 42.9 kg/d), and protein yield (1.38 vs. 1.33 kg/d) than did cows fed tall CS. Cows fed low-NDF diets had greater DMI (25.9 vs. 28.2 kg), yields of milk (42.6 vs. 45.5 kg/d), and protein (1.28 vs. 1.42 kg/d), but lower ECM/DMI (1.73 vs. 1.64) than cows fed high-NDF diets. The apparent total-tract digestibilities of NDF and CP were greater for diets with br2 than tall CS, and high-NDF diets had greater total-tract digestibilities of NDF, starch, and CP than low-NDF diets. Lastly, CH4 output (520 vs. 460 g/d), CH4/DMI (20.1 vs. 17.0 g/kg), and CH4/ECM (11.5 vs. 10.1 g/kg) were greater for cows fed high NDF than low NDF but not altered by corn hybrid. We observed no interactions of hybrid × fiber content, except for DMI, where the increase in DMI from feeding br2 compared with tall CS was greater in the high-silage, high-NDF diets. In conclusion, br2 CS increased productivity of lactating cows compared with CS from a tall hybrid of similar NDF and starch content.