Digestibility, ruminal fermentation, nitrogen balance and methane production in Holstein steers fed diets containing soy sauce cake at 10 or 20%.

Two feeding trials were performed to evaluate the effect of soy sauce cake (SSC) on digestibility, ruminal fermentation and nitrogen (N) balance as well as methane production in Holstein steers. Six animals received a diet without or with the SSC at 10% (Experiment 1) and 20% (Experiment 2) in a 2 × 2 crossover design with a balance trial and respiratory exchange measurement. The SSC feeding showed a strongly inhibitory effect on methane production when its proportion was elevated up to 20%. The digestibility of nutrients with the 10% SSC treatment was similar to that of the control, whereas that for the 20% SSC treatment was significantly decreased in comparison with the control. The 20% SSC treatment also inhibited ruminal fermentation. A lower N partition to urine and a higher N partition to retention were observed in the animals receiving the 20% SSC treatment. These results suggested that SSC feeding at 20% suppressed methane production and changed the N balance; however, the feeding level of 20% caused deterioration in some productive aspects, such as nutrient digestibility and ruminal fermentation. In addition, a feeding level of SSC at 10% of the diet should be considered a reasonable level in cattle.