Methane formation in faunated and ciliate-free cattle and its relationship with rumen volatile fatty acid proportions

Abstract

1. Twelve steers fitted with rumen cannulas were used in three separate experiments to investigate the effects of the presence or absence of rumen ciliate protozoa on methane production. The diet consisted of 850 g barley and 150 g protein supplement/kg, and was given in three feeds daily at a restricted level of 61 g/kg live weight^0.75. Animals were defaunated initially by allowingad lib. consumption of this diet and were then maintained ciliate-free by isolation or were faunated by inoculation with a mixed ciliate suspension. Samples of rumen fluid were taken routinely for the assessment of microbial populations and for volatile fatty acid (VFA) analysis and energy and nitrogen balances and digestibility measurements were made at intervals while animals were confined in respiration chambers.2. In each experiment the rumen VFA proportions changed from a high-propionate pattern under ciliate-free conditions to a low-propionate, high-butyrate pattern in the presence of ciliates: differences between treatments were highly significant (P < 0.001). There were also marked differences between treatments in CH, production but a reliable comparison was possible only in Expt 3, in which CH₄was significantly higher (P < 0.001) in the presence of a rumen ciliate population. In Expt 3 the increased loss of energy as CH₄in the faunated animals amounted to 44 MJ/100 MJ energy intake.3. Stoichiometric estimates of CH₄production derived from the observed VFA proportions showed good agreement with CH₄production as measured in respiration chambers. On average, the stoichiometric CH₄values overestimated CH₄production by a factor of 1.08.4. Highly significant linear relationships (P < 0.001) were observed between the molar proportion of each major VFA and the quantity of CH₄produced: the proportion of propionic acid was inversely related to CH₄and showed the lowest residual standard deviation of all the relationships examined.5. The losses of energy in faeces and urine did not differ between treatments hence the increased loss of energy as CH₄in the faunated animals resulted in a significant reduction in the metabolizability of the diet from 0.73 to 0.69 (P < 0.05). No significant differences were detected between treatments in heat production, apparent digestibility coefficients or N balance.6. It is suggested that the rumen ciliates, by modifying the rumen VFA proportions, are directly responsible for the increased CH₄production in faunated animals.