Ruminal degradation characteristics of neutral detergent fibre (NDF), starch and crude protein (CP) in concentrate ingredients were estimated in dairy cows using nylon bag incubations. Soluble fraction (starch, CP), undegradable fraction (NDF, CP), lag time (NDF) and rate of degradation of the insoluble but degradable fraction (NDF, starch, CP) were measured and showed large variation. Based on measured and partly estimated characteristics ratio's were calculated between total rumen available CP and carbohydrates, between soluble CP and soluble carbohydrates and between insoluble rumen available CP and insoluble rumen available carbohydrates. Ratio's varied largely between feeds and between soluble and insoluble fractions. It is concluded that such ratio's can be used to optimize the composition of concentrates with regard to rumen fermentation. (Abstract retrieved from CAB Abstracts by CABI’s permission)

S U M M A R YIn three experiments, carried out in 1985 and 1986 in the Netherlands, the effects of herbage maturation and rate of nitrogen fertilization on rumen degradability of organic matter (OM) and crude protein (CP) in fresh herbage (Lolium perenne) were studied using the nylon bag technique. Experimental farms at Lelystad and Swifterbant (clay soil) and Achterberg (sandy soil) provided the herbage samples. From the results, the content of digestible CP entering the small intestine (DPI) was estimated.Crude protein content and in sacco degradability of OM and CP decreased with increasing grass maturity and with decreasing rate of N application. With every 100 g/kg DM decrease in CP content, the estimated content of DPI decreased by 19 g/kg DM, no matter how the CP content was manipulated.

Degradation in the rumen of dairy cows of nitrogenous compounds in 35 grass silages and 12 grass hays was studied by means of the nylon bag incubation technique. Silages varied in dry matter content, crude protein content and date of harvesting; hays varied mainly in crude protein content. Measurements in both forages were washable (W), degradable (D) and undegradable fraction (U) and rate of degradation (ks) of D. W and U were measured as the residue after washing without incubating (W) or after 336 h in the rumen (U). N escape (E) was calculated from these data, assuming a ruminal passage rate of 4-5'% per hour. E (N escape from the rumen) in hays was substantially higher than in silages, mainly because a large proportion of N compounds in silage became soluble during the ensiling process. Of the total variation in E, around 80% could be explained in both forages. In silage, E was positively influenced by dry matter content, negatively by crude protein content and positively by the number of days elapsed since 1 April. This effect of day of harvesting was mainly through an increase of U and may not be beneficial to the animal. In hays crude protein content was the major factor explaining variation in E.

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