The aim of the present study was to determine the effects of the potential methane reducer
fumaric acid on the fattening performance and acid-base balance of growing bulls fed two different silage types as
roughage (maize and grass silage). A total of 62 fattening bulls (German Holstein breed, initial
body weight: 266 +/- 42 kg), randomly assigned to eight feeding groups, received four levels of
fumaric acid (0, 100, 200 or 300 g/
d) at each silage type. The daily feed and water intake and the live weight were measured over the whole testing period of 280 days. In blood samples, blood cells and blood
gases as a parameter of
acid-base status were analysed. Feed and faeces were collected to determine the apparent nutrient digestibility. Five animals from each group fed maize or grass silage, supplemented with 0 g or 300 g
fumaric acid, were slaughtered at 580 kg
body weight. After slaughter, rumen fluid pH was measured and dressing percentage was calculated. Neither the total feed intake (8.81 +/- 0.07 kg/d) nor the daily
weight gain (1277 +/- 24 g/d) was influenced significantly by treatments.
Fumaric acid supplementation did not influence the erythrocyte count or the blood gas concentration. The silage type significantly influenced the apparent digestibility of the whole diet. The dressing percentage was slightly higher (p < 0.1) after
fumaric acid supplementation. No signs of an incompatibility to
fumaric acid on the animals were observed over the whole experimental period. However, it seems to be necessary to conduct more long-term studies with different silage types and addition of organic
acids combined with direct measurements of methane.