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Title: Intake, Digestibility and N Balance of Steers Fed Gamagrass Baleage Topdressed at Two Rates of N and Harvested at Sunset and Sunrise.

Author
item SAUVE, A - North Carolina State University
item HUNINGTON, G - North Carolina State University
item WHISNANT, C - North Carolina State University
item Burns, Joseph

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2009
Publication Date: 1/25/2010
Citation: Sauve, A.K., Hunington, G.G., Whisnant, C.S., Burns, J.C. 2010. Intake, Digestibility and N Balance of Steers Fed Gamagrass Baleage Topdressed at Two Rates of N and Harvested at Sunset and Sunrise. Crop Science. 50:427-437

Interpretive Summary: The potential of increasing the total nonstructural carbohydrates (TNC) in perennial grasses by delaying cutting until the late PM has been shown. This has resulted in improved quality of the subsequent hay as expressed by increased steer dry matter intake or dry matter digestibility, or both. Because of the difficulty of making hay in the humid Eastern U.S., attributed mainly to the high humidity and frequency of PM showers, delaying cutting until the PM results in a days loss of drying time. This study examined the potential of baling gamagrass directly after cutting in the PM and the AM, wrapping the bales with plastic and preserving the forage as baleage. Gamagrass was produced under two rates of nitrogen with the idea that the excess TNC would be combined with excess nitrogen to increase nitrogen utilization.. Gamagrass cut in the PM had greater concentrations of TNC compared with the AM and gamagrass receiving the high nitrogen rate had greater nitrogen concentrations. After fermentation, however, 75% of the TNC fraction had been converted to either short chained fatty acids or alcohols and essentially lost to the fermentation process in the rumen. The greater nitrogen concentration was instrumental in improving the digestibility of DM, cellulose and nitrogen digestion. Gamagrass ensiled and stored well as baleage and was readily consumed by steers. However, the strategy of improving quality by harvesting in the PM was not achieved due to the conversion of TNC to fermentation products.

Technical Abstract: The diurnal accumulation of soluble carbohydrates in forages 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-1, direct baled after mowing in the PM (PM/LO and PM/HI) and AM (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. Steer DMI was not altered by harvest time or N rate (mean = 1.87 kg 100-1 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-1) as was cellulose digestion (P = 0.02; 656 vs. 617 g kg-1). The digestion of CP was greater (P =0.01) in the AM vs. PM baleage (519 vs. 443 g kg-1) and greater (P = 0.02) in HI vs. LO N rate (520 vs. 441 g kg-1). Fermentations differed (P < 0.01) between PM and AM baleage as pH averaged 5.4 vs. 4.5. 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) pre-baling was 120 g kg-1 in the PM and 97 g kg-1 in the AM, but after fermentation, averaged < 38 g kg-1 and explains the lack of steer response to the PM harvest. Gamagrass preserved well as baleage and was readily consumed by steers, however, the TNC fraction was not preserved.