No abstract

Two experiments were conducted to evaluate the influence of supplemental aminooligosaccharides (AOS) on the disappearance and fermentation of diets for lactating cows, and its effects on milk yield and quality. In the first study, diets containing 0 or 0.2% AOS (dry matter basis) were incubated for 24, 48 and 72 h with ruminal fluid to evaluate the in vitro dry matter disappearance (IVDMD) and fermentation characteristics. The addition of AOS improved IVDMD of diets, induced higher total bacterial and cellulolytic bacterial counts and decreased the number of bacteria that produce lactate compared to the control. At 24 h incubation, AOS increased volatile fatty acid concentrations and the molar proportion of propionate, though at 48 and 72 h incubation AOS did not affect the fermentation characteristics of the diets. In a further experiment, milk yield and milk quality were evaluated using 50 Holstein dairy cows (193 days in milk). Cows were randomly assigned to the diets tested in the in vitro study. Feed intake was not modified by AOS. Milk yield of cows fed AOS was significantly higher than that of cows not supplemented. Because AOS tended to decrease the percentage of fat in milk, fat and solid-corrected milk content were similar for the two treatments. Percentage and yield of non-fat solids, protein and lactose, and the somatic cell count in milk were not affected by AOS. The milk urea-N concentration of the cows fed AOS was lower than of those not supplemented. Supplementing AOS enhanced the disappearance and fermentation characteristics of the diet. Further studies with cows earlier in lactation are necessary to evaluate the effects of AOS on milk yield and milk components.

One in vitro assay and one in vivo trial with ruminally cannulated Holstein steers were conducted to evaluate the effects of a dietary substitution of soybean meal by a urea and slow-release urea source of fermentation and degradation of diets for cattle. The experimental diets consisted of the total mixed rations defined as the control with soybean meal (SBM), U (urea), SRU (slow-release urea), and SRU+U+AA (0.42% + 0.42% + 1% amino acids methionine and lysine). The dietary substitution of SBM by U or SRU reduced (P < 0.05) the total gas production (V), microbial mass and degradation at 72 h incubation under the in vitro conditions, as well as the degradation rate (c) and the total volatile fatty acids (VFA) in the rumen of the steers; however, when the dietary substitution of SBM was by U+SRU+AA, those values did not decrease. In the steers, the dietary substitution of SBM by U and SRU reduced the ruminal degradation rate and the total VFA, and increased the ammonia N, but when SBM was substituted by U+SRU+AA in the diets, these changes were not observed. No advantage of SRU over U was found. The dietary substitution of SBM by U, SRU, U+SRU+AA did not modify the molar proportion of the VFA in the rumen nor were there changes in the nutrient digestion or excretion. Both the in vitro assay and the in vivo trial indicated that replacing SBM with U or SRU increases the ruminal ammonia N concentrations and reduces the degradation rate in the rumen, although those undesirable findings were not found when the SBM was replaced by U+SRU+AA. Therefore, it is feasible to replace the SBM with a combination of urea, slow-release urea, lysine and methionine in the diet for the ruminants.