Roughage Sources and Levels in Steer Rations

Abstract

Two feedlot trials were conducted to study the performance of steers fed rations containing 5 or 20% rice straw, alfalfa hay, rice hulls, 5% oyster shells and all-concentrate. Total consumption of the 20% rice straw ration was greater than for other rations. However, concentrate intake was similar for the two levels of rice straw. The difference in carcass weights can be largely explained by concentrate intake. The similar concentrate intake, gain and carcass weight of rice straw fed steers suggest that 5% rice straw is adequate under conditions of this experiment while a comparison with the all-concentrate ration suggests that some roughage is needed. Alfalfa hay, possibly because of the fineness of grind did not satisfy this need. Gains, carcass weights and grades of steers fed 20% rice hulls, or 5% oyster shells were lower than when other rations were fed, indicating that these are not satisfactory roughage replacers at these levels. These data suggest that the response of fattening steers to roughage level depends on roughage source. Rumen fluid from steers fed 20% rice straw had the highest pH followed by rumen fluid from steers fed 20% rice hulls which was higher than from steers fed all-concentrate, 5% alfalfa hay, rice hulls or oyster shells Total volatile fatty acid concentration followed an inverse pattern in that rumen fluid from steers receiving 20% rice straw had a lower concentration than from steers fed other rations. Rumen fluid from steers fed 20% rice straw had more acetate and less propionate than from steers fed 20% rice hulls and the fluid from both had more acetate and less propionate than from steers fed other rations.