UTILIZATION OF GRASS-SILAGE BY CATTLE - EFFECT OF SUPPLEMENTATION WITH DIFFERENT SOURCES AND AMOUNTS OF PROTEIN

Forty-eight crossbred beef steer calves, initial live weight of 260 kg , were used to examine production responses when grass silage was supp lemented with fish meal (FM) or soybean meal (SBM) during a 210-d feed ing period. The silage was available on an ad libitum basis either alo ne or supplemented with 100, 225, 350, or 500 g of FM or 600 g of SBM/ d. Increasing levels of FM resulted in a linear increase in live weigh t gain (P <.001) and gain:feed ratio (P < .001). The FM supplementatio n had no effect (P =.79) on silage DM intake. The FM supplement increa sed plasma albumin concentration (P <.05) but did not affect plasma gl ucose (P >.20) The steers were shipped to market when they had 8 mm of fat over the longissimus muscle as determined by ultrasound. Sensory evaluation of roasts from steers fed 0, 225, 350, or 500 g/d of FM ind icated a positive linear (P <.01) increase in flavor and decrease in j uiciness as FM level increased. There were no differences (P >.15) in live weight gain, intake, or gain:feed ratio between isonitrogenous su pplements of FM and SBM. However, the additional gain resulting from S BM and FM indicated that, on a crude protein basis, SBM was approximat ely 80% as effective as FM in increasing live weight gain in steers fe d grass silage.