EFFECT OF INCREASING THE DIETARY LEVEL OF RAPESEED MEAL ON INTAKE BY GROWING BEEF STEERS

Three experiments were conducted to determine the effects of rapeseed meal on intake by cattle. In the first experiment, the effect of incre asing rapeseed meal level on intake, growth, and performance of growin g beef steers was evaluated. In the second experiment, the effect of e xtrusion (glucosinolate reduction) on supplement intake by steers was evaluated. In the third experiment, the effect of increasing dietary r apeseed meal level on supplement intake was evaluated. In the first ex periment, rapeseed meal replaced soybean meal at 0, 33, 67, or 100% of the supplemental protein. Dry matter intake, crude protein intake, an d serum thyroxine levels were decreased linearly (P < .01) with increa sing level of rapeseed meal in the supplement. Protein sources used in Exp. 2 were soybean meal, rapeseed meal, extruded rapeseed meal, and soybean meal containing rapeseed oil at the same level as the rapeseed meal. In Exp. 3, the protein sources were composed of different combi nations of rapeseed meal and soybean meal (100% rapeseed meal; 67% rap eseed meal and 33% soybean meal; 33% rapeseed meal and 67% soybean mea l; and 100% soybean meal). Supplement intake was measured at .5, 4, an d 24 h after feeding in both experiments. Extrusion treatment, which r educed glucosinolate content in rapeseed meal 75%, did not improve (P > .10) supplement intake. Rapeseed meal resulted in lower supplement i ntakes at .5 and 4 h than the Soybean meal and soybean meal + rapeseed oil supplements (P = .003). Increasing level of rapeseed meal in the supplement resulted in a linear decrease in supplement intake at .5 an d 4 h (P < .0001) and a trend (P = .08) toward decreased supplement in take at 24 h. From this research we concluded that high levels of rape seed meal will reduce intake by cattle.