The production of volatile fatty acids in sheep on different pasture types : a thesis presented in partial fulfilment of the requiremenrts for the degree of Master of Agricultural Science at Massey University

The New Zealand economy depends largely on the efficient conversion of pasture to exportable animal products. The current emphasis on higher stocking rates increases the need for pastures best suited to animal production. Pasture species used in New Zealand are recognised as differing in their effects on animal production, these differences being loosely attributed to variation in "pasture quality". If the level of output of saleable product is the accepted measure of pasture quality, then the principal factors governing this are the quantity of feed consumed and its subsequent utilisation. A number of studies have shown that differences in food intake alone cannot account for the observed differences in animal performance. It has thus been considered important to investigate the factors affecting the utilisation of pasture by the animal. Volatile fatty acids (VFA) produced in the rumen are generally considered to account for 70 to 60 percent of the net energy requirements of ruminants, and their production must be a major determinant of feed utilisation. Differences in the ruminal concentrations and proportions of VFA have often been observed with pasture feeding and have been cited as possible reasons for differences in pasture quality. The investigation described here was undertaken as a preliminary study of the role of VFA production in determining the quality of New Zealand pasture species