THE EFFECTS OF INCREASING DIETARY ROUGHAGE LEVEL AND SLAUGHTER WEIGHT ON THE FEEDLOT PERFORMANCE AND CARCASS CHARACTERISTICS OF BULLS AND STEERS

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Abstract
A serial slaughter experiment is described comparing 45 bulls and 44 implanted steers. Nine of each "sex" were slaughtered at the start of the trial and the remaining 71 were fed diets containing three roughage levels (20%, 50% and 80% alfalfa–brome hay) to two pen-average slaughter weights (450 kg or 580 kg). Cattle were about 12 mo old at the start of the trial, and bulls were heavier (290 kg vs. 269 kg) than steers. Increasing the level of roughage in the diet resulted in a significant decrease in average daily gain (ADG), and an increase in feed intake and feed per kilogram gained to both slaughter weights. Differences in digestible energy (DE) intake were not significant. Apparent digestibilities of dry matter, crude protein and DE were significantly decreased, and acid detergent fiber significantly increased, by increasing levels of roughage. Bulls grew faster than steers and required less feed per unit of gain to both slaughter weights. Increasing the level of roughage decreased warm carcass weight, dressing percent and all measures of carcass fatness to both slaughter weights. Cattle fed low levels of roughage reached an optimum grade (A1) at a lower carcass weight than those fed high levels of roughage, and remained in that grade for a shorter period of time. Fat-free body size tended to increase with roughage level. Steer carcasses were fatter than those of bulls and had lighter sample muscle weights and smaller sample muscle to bone ratios. Based on present feed costs the lowest roughage diet produced the cheapest liveweight gain.

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