In vitro mixed ruminal microorganism fermentation of whole cottonseed coated with gelatinized corn starch and urea

We conducted an in vitro mixed ruminal microorganism fermentation study to determine the effect of coating whole cottonseed with gelatinized corn star ch and feed grade urea. Treatments were arranged as a 3 x 4 factorial to pr ovide three concentrations of starch (0.0, 2.5, and 5.0%) and four concentr ations of urea (0.0, 0.25, 0.5, and 1.0%). All treatments were prepared fro m one lot of whole cottonseed. Batch culture fermentations were conducted u sing anaerobic medium that contained 20% (vol/vol) ruminal fluid in 160-ml serum bottles. Whole cottonseed was ground to pass through a 6-mm screen an d weighed amounts (0, 0.4, 0.8, and 1.2 g) were added to the serum bottles. As starch increased, H-2, CH4, total volatile fatty acids, and molar propo rtions of propionate increased linearly, whereas pH, molar proportions of a cetate, and the acetate to propionate ratio decreased linearly. L-Lactate c oncentrations were highest with 2.5% starch compared with 0 or 5.0%. As the amount of urea in the coating increased, pH and CH4 increased linearly, wh ereas H-2 concentrations decreased linearly. Ammonia concentrations exhibit ed a quadratic response due to moderate increases with the addition of 0.25 and 0.5% urea, and a greater increase was observed with 1.0% urea. Interac tions between starch and urea were observed for H-2, CH4, NH3, and L-lactat e. Concentrations of H-2 decreased and CH4 was relatively constant as urea increased in the presence of 0 and 2.5% starch, but increased with 5% starc h. L-Lactate concentrations were unchanged (0% starch), higher (2.5% starch ), or lower (5.0% starch) as urea increased. Ammonia concentrations increas ed after urea exceeded 10% of the starch concentration. The addition of ure a did not prevent the decline in pH, but did reduce H-2 and CH4 accumulatio n with 2.5% starch.