Relationships Between Fiber in Feedlot Diets and Growth Performance of Beef Cattle

A database (110 treatment means from 23 studies) was derived from the peer-reviewed literature to evaluate the effects of various measures of dietary fiber on growth performance of feedlot cattle. The measures of diet fibrousness were the percentage of traditional roughage sources in the diet, the percentage of neutral detergent fiber (NDF) supplied by traditional roughages, and the total dietary concentration of NDF. The growth performance variables evaluated were dry matter intake, average daily gain, gain-feed ratio, and hot carcass weight. Mixed-model regression methods were used to adjust for random slope and intercept effects associated with studies, and study-adjusted data were evaluated to assess the effects of each of the measures of fibrousness on each of the measures of growth performance. The quality of the regression relationships was assessed by determining the significance of slope and intercept estimates, the root mean square error and the associated coefficient of variation, and the coefficient of determination (r²). In contrast to a previous analysis of literature data, 60% of the studies in the present database included fibrous byproducts (primarily wet corn gluten feed and wet or dry distillers grains plus solubles). Among the growth performance variables, measures of fibrousness were most highly correlated with dry matter intake (total consumed per day or percentage of average body weight), and among the measures of fibrousness, total dietary NDF concentration consistently accounted for the largest percentage of variation in growth performance variables. For dry matter intake as a percentage of body weight, total dietary NDF concentration accounted for 63.3% of the variation in dry matter intake, compared with 19.6% and 29.9% for NDF from roughage and percentage of roughage in the diet, respectively. Similarly, total dietary NDF concentration accounted for 58.1% of the variation in total dry matter consumed per day, compared with NDF from roughage (18.3%) and the dietary percentage of roughage (25.9%). For each 1% increase in total dietary NDF, dry matter intake increased by approximately 0.023% of body weight or 0.11 kg/d. Average daily gain and hot carcass weight were not strongly associated with measures of fibrousness (r² values ranged from 0.001 to 0.122), reflecting the ability of feedlot cattle to compensate for lower dietary energy concentrations as NDF increased in the diet, at least within the ranges of NDF evaluated in the current database. As expected, with increased dry matter intake and little change in average daily gain, the gain-feed ratio was negatively associated with measures of fibrousness, with an r² value of 0.296 for the total dietary NDF concentration. Although more research is needed on the role of physically effective NDF in feedlot diets, present data confirm previous observations about the relationship between the total dietary NDF concentration and dry matter intake, extending this relationship to feedlot diets that contain substantial proportions of fibrous byproducts. The total dietary NDF concentration in feedlot diets should be an effective basis for exchanging dietary ingredients to maintain a similar growth performance of feedlot cattle.