IN-SACCO DEGRADATION CHARACTERISTICS OF ORGANIC-MATTER, NEUTRAL DETERGENT FIBER AND CRUDE PROTEIN OF FRESH GRASS FERTILIZED WITH DIFFERENT AMOUNTS OF NITROGEN

Thirty composite grass samples, containing mainly Lolium perenne, were taken at three measuring periods in the spring and summer of 1991 and 1992 and two in the autumn of 1992 and 1993 from plots fertilized wit h 150, 300 and 450 kg N ha(-1) year(-1), In each period X N plot combi nation, grass samples were taken at a dry matter (DM)-yield of 1500 to 2000 kg ha(-1) over four consecutive days and subsequently combined t o one composite sample. These samples were incubated in rumen and inte stinal cannulated lactating cows using the nylon-bag and mobile-nylon bag techniques to study the effects of N fertilizer on rumen degradati on of organic matter (OM), crude protein (CP) and neutral detergent fi bre (NDF) and on the intestinal digestibility of ruminal escaped CP (D RE(CP)), Nitrogen fertilizer increased CP content and decreased the co ntent of DM and sugar whereas NDF content and in vitro digestibility ( d(OM)) were not markedly influenced. The NDF content and d(OM) were mo re related to differences in age of the grass than to differences in t he amounts of N applied. The content of neutral detergent insoluble N (NDIN) was increased significantly at higher rates of N fertilization. However, this effect on NDIN was difficult to interpret because of th e fact that NDIN was highly influenced by the method of sample prepara tion, The N fertilizer had no effect on the content of acid detergent insoluble N (ADM) which was negligible compared to the level of NDIN. The washable OM fraction was not influenced by N fertilizer whereas th e washable CP fraction increased significantly. The results showed a d ecrease of the undegradable OM, CP and NDF fractions by using more N f ertilizer. The rate of degradation of potentially degradable, but inso luble OM, CP and NDF fractions increased significantly at higher level s of N fertilization. As a consequence, more N fertilizer decreased th e fraction of ruminal escaped CP (RE(CP)) significantly. However, duri ng the whole season the total amount of RE(CP) entering the small inte stine was increased although the increase was more pronounced in sprin g and early summer than in late summer and autumn. Only in autumn smal l intestine digestibility of RE(CP) tended to be higher at higher rate s of N fertilization.