Factors affecting in situ dry matter degradability of tropical forage:: 1.: Basal diet

Samples of alfalfa (Medicago sativa L.), braquiaria (Brachiaria decumbens Stapf), coast-cross (Cynodon dactylon x Cynodon nlemfuensis), jaragua (Hyparrehnia rufa Ness.) all milled to 5mm and braquiaria cut to 15mm were incubated in nylon bags for 6, 24 and 96 hours in rumen of three fistulated steers. During the first experimental phase, the animals were daily fed with jaragua hay, 2.4kg concentrate, and 25g mineral mixture. During the second phase, they were fed with alfalfa hay and mineral mixture only. The objective was to study the diet effect upon the parameters estimates of in situ dry matter degradability equation, DMD=A-B.e(-ct). The so obtained parameters for alfalfa were nor affected by diets. The value of the degradation potential for 5mm jaragua was greater with alfalfa diet. For 5mm coast-cross, 5mm braquiaria and 15mm braquiaria, using jaragua diet, the adverse conditions caused low values for degradation rate, affecting the application of the Orskov equation. Except for 5mm jaragua and alfalfa all other forages tested under jaragua diet found adverse ruminal condition in terms of microbial activity caused by low level of protein (3.3%) and their data could not be fitted in the suggested model.