Unique interrelationships between fiber composition, water-soluble carbohydrates, and in vitro gas production for fall-grown oat forages

Authors: Coblentz, Wayne; NELLIS, SAMANTHA - University Of Wisconsin; HOFFMAN, PATRICK - University Of Wisconsin; Hall, Mary Beth; Weimer, Paul; ESSER, NANCY - University Of Wisconsin; BERTRAM, MICHAEL - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2013
Publication Date: 10/25/2013
Publication URL: http://handle.nal.usda.gov/10113/57941
Citation: Coblentz, W.K., Nellis, S.A., Hoffman, P.C., Hall, M., Weimer, P.J., Esser, N.M., Bertram, M.G. 2013. Unique interrelationships between fiber composition, water-soluble carbohydrates, and in vitro gas production for fall-grown oat forages. Journal of Dairy Science. 96:7195-7209.

Interpretive Summary: Fall-grown oat forages that undergo winter-hardening in response to cold temperatures during the late-elongation or early-boot stages of growth can exhibit abnormally high concentrations of water-soluble carbohydrates (sugars). This phenomenon, where the forage plant produces more energy late in the plant’s life, is highly unusual among forages; it suggests that fall-grown oat can be utilized to extend the grazing season, or to produce a high-energy, late-season forage in northern latitudes. In order to evaluate how dairy cattle might react to this phenomenon, we evaluated in vitro gas production of selected fall-oat forages (to estimate rumen fermentation). Microbial fermentation, as measured by cumulative in vitro gas production, was accelerated at early incubation times, specifically in response to this large pool of rapidly fermentable carbohydrates. While unique in vitro fermentation characteristics of these forages were observed, production trials with lactating cows are needed to determine how to use these forages most efficiently in dairy diets. The highly sugared oat forages evaluated in this study exhibited estimates of energy density that were comparable to corn silage. It may be possible to replace some corn silage in dairy diets with fall-oat forage, thereby limiting starch within the diet, and providing more options for cropping rotations in dairy enterprises.

Technical Abstract: Recently, several research projects evaluated the potential of fall-grown oat (Avena sativa L.) for use as emergency fall forage to extend the grazing season, or for routine use as an additional forage production option. Sixty samples of ‘ForagePlus’ oat were selected from a previous plot study for analysis of in vitro gas production (IVGP) on the basis of 2 factors: i) high (N = 29) or low (N = 31) neutral detergent fiber (NDF; 62.7 ± 2.61 and 45.1 ± 3.91%, respectively); and ii) the range of water-soluble carbohydrates (WSC) within the high and low-NDF groups. For the WSC selection factor, concentrations ranged from 4.7 to 13.4% (mean = 7.9 ± 2.06%) and from 3.5 to 19.4% (mean = 9.7 ± 4.57%) within high- and low-NDF forages, respectively. Our objectives were to assess the relationships between IVGP and various agronomic or nutritional characteristics for high and low-NDF fall-oat forages. Cumulative IVGP was fitted to a single-pool nonlinear regression model [Y = MAX × (1 – e (–K × (t – lag)))], where Y = cumulative mL of gas produced, MAX = maximum cumulative mL of gas produced at infinite incubation time, K = rate constant, t = incubation time (h), and lag = the discrete lag time (h). Generally, cumulative IVGP after 12, 24, 36, or 48 h within high-NDF fall-oat forages was negatively correlated with NDF, hemicellulose, lignin, and ash, but positively correlated with WSC, nonfiber carbohydrate (NFC), and total digestible nutrients (TDN). For low-NDF fall-oat forages, IVGP was positively correlated with growth stage, canopy height, WSC, NFC, and TDN; negative correlations were observed with ash and crude protein (CP), but not generally with fiber components. These responses also were reflected in multiple regression analysis for high- and low-NDF forages. After 12, 24, or 36 h of incubation, cumulative IVGP within high-NDF fall-oat forages was explained by complex regression equations utilizing (lignin/NDF)2, lignin/NDF, hemicellulose, lignin, and TDN2 as independent variables (R2 = 0.432). Within low-NDF fall-oat forages, cumulative IVGP at these incubation intervals was explained by positive linear relationships with NFC that also exhibited high coefficients of determination (R2 = 0.749). Gas production was accelerated at early incubation times within low-NDF forages, specifically in response to large pools of WSC that were most likely to be present as forages approached boot stage by late-fall.