The protection of the unsaturated fatty acids of dried grass and sunflower seed against biohydrogenation by rumen micro-organisms : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University

Abstract

Ryegrass which had been dried and treated with HCHO was incubated with the rumen contents of a pasture-grazed cow. The protein in the grass was protected from degradation by the rumen microbes. The degree of protection of the protein increased with the rate of HCHO application over the range 0.5-2.0 g HCHO per 100 g of dried grass. At the highest rate of HCHO application, the digestibility of the forage dry matter (measured in vitro) was a little less than that of the untreated forage. In vitro incubations with rumen fluid also showed substantial protection of 18:3 in dried grass which had been treated with HCHO. Again, the degree of protection increased with the rate of application of HCHO. The upper level of HCHO treatment which was also the optimum was higher than the level recommended by other workers for the protection of protein in dried forage. Dried grass obtained from a commercial source was treated with HCHO (2 g HCHO/lOO g dried grass) and was fed to a cow from a monozygous twin pair. Intake was reduced and an underfeeding response was observed. The proportions of 18:2 and 18:3 in the milk fat of the cow were not elevated. This lack of response probably was due to a combination of the depressed intake by the cow and the low levels of endogenous lipid (compared with spring pasture) in the grass used. A supplement of sunflower seed and casein which had been treated with HCHO was fed to a cow. Milk fat containing about 10 moles % 18:2 was produced. When a supplement of sunflower seed and casein which had not been treated with HCHO was fed, a much smaller increase in the content of 18:2 in the milk fat was observed.