Assessment and control of conditions in the rumen to increase utilization of fibrous roughages in ruminants
CHAPTER 2 Five experiments were conducted to investigate the dietary factors within the rumen environment which could contribute to the rate of degradation of straw. Three sources of digestible cellulose and/or hemicellulose (unmolassed sugar beet pulp, citrus pulp and dried grass) and two sources of natural proteins (fish meal and soya bean meal) were investigated for their ability to increase degradation of straw In. sacco in sheep, as supplements to untreated straw. The untreated straw used in these experiments was adequately supplemented with rumen degradable nitrogen, sulphur, vitamins and minerals. Unmolassed sugar beet pulp and dried grass when given at a level of 150 g.kg DM-1, increased both the rate and extent of DM degradation of straw In sacco. Citrus pulp and soya bean meal had no effect on straw degradation while fish meal increased the extent of straw DM degradation. The rumen NH3 levels and pH in both the control and supplemented animals were above the range that would be expected to cause an inhibition in fibre digestion. It was concluded that digestible cellulose/hemicellulose and fish meal improved the conditions in the rumen for fibre degradation in animals given straw diets. CHAPTER 3 The supplementary effects of unmolassed sugar beet pulp and fish meal on intake, digestibility and growth performances of sheep, given either untreated or ammonia treated straw, were investigated using twenty four sheep. The experimental design was a 2 x 2 x 2 factorial layout. Unmolassed sugar beet pulp and fish meal increased untreated straw digestibility by 10% and intake by 16-22%. The supplements had no effect on the digestibility or intake of basal ammonia treated straw. Ammonia treatment alone however increased the intake and digestibility of untreated straw by 76% and 16%, respectively. The growth achieved in this experiment was highly correlated to the intake of total digestible DM. CHAPTER 4 Two experiments were conducted to study the supplementary effects of unmolassed sugar beet pulp and fish meal on intake, digestibility and growth performance of cattle given either untreated or ammonia treated straw. Twenty four Hereford x Friesian steers and thirty two Friesian cross steers and bulls were used for the two experiments respectively. The first experiment was conducted for ten weeks, while the second experiment was continued for twenty weeks. Both the experiments were of 2 x 2 x 2 factorial design. Unmolassed sugar beet pulp and fish meal when given in a combination increased the intake and digestibility of untreated straw. Similar to the results of the sheep experiment (Chapter 3) these supplements did not change the intake or digestibility of ammonia treated straw. Ammonia treatment however increased the intake by 22 and 2 and digestibility by 26 and 14% in these two experiments. The growth observed in the first experiment was higher than expected, but in both experiments growth was related to total digestible DM intake. CHAPTER 5. Methods to predict the rate and extent of roughage degradation in different rumen environments were investigated. The activities of two particle-bound microbial enzymes were measured, glutmate dehydrogenase (GDH) and carboxymethyl cellulase (CMCase). A method was developed and standardized to measure particle-bound microbial enzymes after incubating straw contained in nylon bags in the rumens of sheep given different diets. Using this method particle-bound enzyme activities were correlated with dry matter degradation in the rumen. Particle-bound NAD-linked GDH activity showed no relationship to dry matter degradation while particle-bound CMCase activity showed a very high correlation with the rate and extent of straw degradation. It was concluded that measuring particle-bound CMCase activity at 8 or 16 hr incubation periods could be useful in predicting the rate and extent of DM degradation of straw. CHAPTER 6 The results were discussed in relation to the view that the 'rate limiting: steps' that control digestion and intake of low quality roughages such as rate of fibre degradation, rate of particle size reduction, and the rate of passage of undigested material from the rumen depend upon: (a) proportion of the fibre-degrading organisms in the total microbial population (b) factors related to the roughage such as 'fragility' (c) animal species (i.e. sheep or cattle). Practical implications of the findings for animal production were evaluated on a nutritional and economical basis and it was concluded that the judicious supplementation of untreated straw with a source of digestible cellulosic/hemicellulosic material and a slowly degrading natural protein could replace ammonia treatment of straw, but has to be reassessed in different parts of the world depending on the availability and cost of the supplements.