Quality Analysis of Summer-Annual Forages. II. Effects of Forage Carbohydrate Constituents on Silage Fermentation
1987
Fisher, D. S. | Burns, J. C.
Fermentation characteristics of many of the sorghum (Sorghum bicolor L.) types and cultivars within types and the consequent relationship between nonstructural carbohydrates and fermentation products of such forages has not been adequately examined. The objectives of this study were to examine fermentation products and changes in nonstructural carbohydrate fractions with ensiling and relate these to the unfermented forage characteristics of one millet (Pennisetum americanum L.), one corn (Zea mays L.), and eight sorghum cultivars. The buffering capacity of unfermented forage was found to be greater (P<0.01) in sorghum (9.8 mL 0.1 M lactate) than in corn (8.0 mL 0.1 M lactate). Starch was less susceptible to degradation during fermentation than sugar. High levels of starch resulted in fermentation and loss of a smaller proportion of the total nonstructural carbohydrates (TNG). Reductions in TNG ranged from 61 g kg⁻¹ for ‘Tifleaf-I’ millet to 239 g kg⁻¹ for ‘NK-367’ forage sorghum at Location 1 and 30 g kg⁻¹ for ‘Savanna-5’ grain sorghum to 167 g kg⁻¹ for NK-367 forage sorghum at Location 2. Predictive equations for the proportion of TNG retained after ensiling were developed using unfermented forage characteristics as independent variables. These regression equations accounted for 70 to 91% of the variation. By weight, the most important fermentation products were lactate (42.9–114.1 g kg⁻¹), acetate (9.4-39.4 g kg⁻¹), and ethanol (1.4–50.0 g kg⁻¹). Only small quantities of substrate were fermented to propionate (0.0ℓ1.3 g kg⁻¹), butyrate (0.3–1.6 g kg⁻¹), and acetaldehyde (0.4–1.3 g kg⁻¹)- Palatability was positively correlated with acetate (r=0.70*), propionate (r=0.91**), and total sugars in the silage (r=0.84**).
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