Yeast cultures and multipurpose fodder trees as feed supplements for ruminants
The research described in this thesis consists of two components. The objective of the first one was to examine the role of yeast culture, based on Saccharomyces cerevisiae, as a rumen modifier and to examine the viability of yeast cells in the rumen and their mode of action in stimulating fermentation. For this purpose, two in vitro and four in vivo experiments were carried out. In vivo and in vitro experiments were undertaken to examine the viability of yeast cells in the anaerobic environment of the rumen. In vivo, the decline in numbers of viable yeast cells in the rumen of sheep receiving YC was slower than the outflow of Cr-mordanted yeast and PEG. In vitro experiments showed a weak growth under anaerobic conditions. It was concluded that yeast cells could not maintain sustainable growth in the rumen because their multiplication rate was slower than the outflow rate. If a yeast could be selected which grew in the rumen, there would be added beneficial effects on fermentation. In the second component, chemical analysis, in situ, 4 in vitro and one in vivo experiments were carried out to examine the potential nutritive value of multipurpose trees (MPTs) and to detect antinutritive factors or toxic substances. The first experiment aimed to study the chemical composition and degradability of MPTs, Medicago sativa hay (alfalfa) and Eragrostis abyssinica (teff). Chemical analyses showed that MPTs are rich in CP and minerals except phosphorous. The in vitro digestibility and in situ nylon bag technique showed that MPTs are promising protein supplements to low protein, poor quality tropical fodders and agricultural by-products and residues, provided their nutritive value is not limited by antinutritional factors.