Short communication: Production response of lactating dairy cows to brachytic forage sorghum silage compared with corn silage from first or second harvest.

A completely randomized lactation trial was conducted to compare the production response of lactating Holstein cows to diets based on corn or forage sorghum silage harvested from 2 crops. Corn was planted in March and harvested in July (corn silage-summer; CSS) and a second corn crop was planted in July and harvested in November (corn silage-fall; CSF). A brachytic dwarf brown midrib forage sorghum was planted in April, harvested in July (forage sorghum-summer; FSS), fertilized, and harvested a second time in November (forage sorghum-fall; FSF). All forage was ensiled in plastic bags and stored until the production trial began. Silages contained (dry matter basis) 8.0, 8.5, 9.0, and 9.5% crude protein; 39.0, 38.3, 54.2, and 55.1% neutral detergent fiber; and 3.6, 2.8. 7.7, and 7.8% acid detergent lignin, for CSS, CSF, FSS, and FSF, respectively. Forty-eight mid-lactation Holstein cows (153.5±37.2d in milk, 35.7±6.2kg/d of milk, 3.2±0.6% fat, 611.8±67.0kg of body weight, and 2.96±0.09 body condition score) were assigned randomly to 1 of the 4diets differing in forage source. Cows were individually fed experimental diets once daily behind Calan doors for 5wk. Diets were formulated to contain 38.7% of the experimental forages and balanced to provide equal concentrations of protein, fiber, and energy. No differences were observed in dry matter intake and yields of milk and components, but milk fat percentage was lower for CSS and CSF compared with FSS and FSF, being 3.20, 2.91, 3.42, and 3.53%, respectively. Milk lactose percentage was lower for CSS compared with CSF but was not different from FSS or FSF. Concentrations of milk urea nitrogen were lower for CSS and CSF compared with FSS and FSF (10.6, 13.4, 14.9, and 15.3mg/dL, respectively). No differences were observed in body weight or body condition score change during the trial. Results of this trial suggest that silage produced from brachytic forage sorghum, as either the first or the ratoon crop, can support similar intake and performance as diets based on corn silage.