Fishmeal supplementation of steers fed on grass silage: effects on rumen function, nutrient flow to and disappearance from the small intestine

Four Hereford Yen Friesian mature steers equipped with rumen, duodenal and ileal cannulas were fed on either grass silage alone (S) or silage supplemented with fishmeal (150 gkg-1 silage dry matter intake; SFM) to assess effects on rumen fermentation, nutrient flow to and disappearance from the small intestine. The silage was a primary growth of perennial ryegrass with a total-N content of 24.5 gkg-1 dry matter (DM). Ruminal concentrations of acetate, butyrate and ammonia-N were not different between treatments and averaged 51.7, 8.9 and 8.4 mmoll-1, respectively. However, molar proportion of propionate was higher on SFM compared to S, 18.7 and 17.6 (SEM 0.18, P <0.05), respectively. The amount and efficiency of microbial protein synthesis were not different between treatments and averaged 71.0 gd-1 and 35.8 g Nkg-1 organic matter digested in the rumen, respectively. Fishmeal supplementation increased the flow of total-N ( P <0.05), non-ammonia-N ( P <0.05), and total amino acids ( P <0.05) at the duodenum. Amino acid disappearance was increased by fishmeal supplementation, 488 and 717 gd-1 (SEM 28.6, P <0.05) for S and SFM, respectively. The apparent absorption coefficient for the total amino acids from the small intestine [(expressed as duodenal - ileal)/duodenal] was also increased, 0.57 and 0.72 (SEM 0.028, P <0.06) for S and SFM, respectively.