Production response of lactating cows to diets based on corn or forage sorghum silage produced from first or second harvest
The objective of the trial was to compare the production response of lactating Holstein cows to corn or forage sorghum silage produced from two crops. Corn was planted in April and harvested in July (CS1). A second crop was planted in July and harvested in November (CS2). A brachytic dwarf forage sorghum was planted in April, harvested in July (FS1), fertilized, and harvested a second time in November (FS2). All forage was ensiled in plastic bags and stored until the production trial began. Silages contained (DM basis) 8.0, 8.5, 9.0, and 9.5% CP; 39.0, 38.3, 54.2, and 55.1% NDF; 3.55, 2.83. 7.72, and 7.77% acid detergent lignin; and 48.1, 47.7, 31.5, and 29.1 NFC, for CS1, CS2, FS1, and FS2, respectively. Forty-eight mid-lactation Holstein cows (153.5 DIM, 36.5 kg milk, and 3.2 % fat) were assigned randomly to one of for diets differing in forage source. Cows were fed individually once daily behind Calan doors for 5 wk. Diets were balanced to provide equal concentrations of protein, fiber, and energy. No differences were observed in DMI, milk yield, or milk composition among treatments: 23.1, 21.1, 21.0, and 19.9 kg/d DMI; 34.5, 34.4, 34.9, and 35.1 kg/d milk; 3.34, 3.22, 3.40, and 3.52% fat; and 2.73, 2.63, 2.61, and 2.65% protein for CS1, CS2, FS1, and FS2, respectively. Concentrations of MUN (mg/dl) were higher (P = 0.03) for FS1 and FS2 compared with CS1 and CS2 (16.2, 16.3, 11.6, and 13.9, respectively). Results of this trial suggest that brachytic forage sorghum silage can support similar as corn silage. Forage harvested from the regrowth of brachytic forage sorghum also supported similar performance as the first harvest. The higher MUN observed for diets based on forage sorghum reflects most likely reflects differences in fermentable carbohydrate compared with corn silage diets.
Keywords: Corn silage, forage sorghum, milk yield