Intake, Digestibility, and Nitrogen Balance of Steers Fed Gamagrass Baleage Topdressed at Two Rates of Nitrogen and Harvested at Sunset and Sunrise

摘要

Maximum diurnal accumulation of soluble carbohydrates in warm-season grasses is an economic way of increasing hay quality; however, in the humid East, haymaking is difficult. This study evaluated gamagrass (Tripsacum dactyloides L.), topdressed with either 56 (LO) or 168 (HI) kg N ha super(-1), direct baled after mowing in the afternoon (PM/LO and PM/HI) or morning (AM/LO and AM/HI), wrapped with plastic film, and conserved as baleage. The four baleage treatments were evaluated by steers for dry matter intake (DMI), digestibility, and N retention. Neither harvest time nor N rate altered DMI (mean = 1.87 kg 100 super(-1) kg body weight). Digestion was similar between PM and AM baleage but greater (P = 0.05) for HI vs. LO N rate (536 vs. 506 g kg super(-1)) as was cellulose digestion (P = 0.02; 656 vs. 617 g kg super(-1)). The digestion of crude protein was greater (P = 0.01) in the AM vs. PM baleage (519 vs. 443 g kg super(-1)) and greater (P = 0.02) in HI vs. LO N rate (520 vs. 441 g kg super(-1)). Fermentations differed (P < 0.01) between PM and AM baleage, as pH averaged 5.4 and 4.5, respectively. Greatest (P < 0.01) amounts of alcohols and least fatty acids occurred in PM baleage and N rate reduced (P < 0.01) alcohols but increased fatty acids. Total nonstructural carbohydrates (TNC) prebaling was 120 g kg super(-1) in the PM and 97 g kg super(-1) in the AM, but baleage averaged <38 g kg super(-1) and explains the lack of steer response to the PM harvest. Gamagrass preserved well as baleage and was readily consumed, but the TNC fraction was not preserved.