Effects of Fish Meal on Nutrient Digestibility and Rumen Fermentation of High-Roughage Rations for Cattle2

The effects of good quality fish meal on nutrient digestibility and rumen fermentation were studied in rumen fistulated steers fed high-roughage diets. A ration with a 1:2.5 concentrate: roughage ratio was fed. The concentrate was a 22% protein supplement and the roughage was low-protein pangolagrass hay. Four levels of fish meal were studied by replacing 0, 33, 66 and 100% of the soybean meal in the concentrate with fish meal on an isonitrogenous basis. The four rations were fed to four mature rumen fistulated Hereford steers in a 4 × 4 latin square design. Fish meal level had no effect on nutrient digestibility, except for crude protein. Average digestion coefficients for all treatments were: dry matter, 59.8%; cellulose, 60.3%; and ether extract, 59.1%. Increasing fish meal level decreased crude protein digestibility from 53.7 to 49.4% (P<.01) and also decreased ruminal ammonia levels 2 and 4 hr. after feeding (P<.01). Total VFA concentrations 2 hr. post-feeding and the molar percent of rumen valerate at 0, 2- and 4-hr, post-feeding were decreased with increasing fish meal levels.