Optimal Dietary Crude Protein Levels for Steer Calves Limit-Fed High-Concentrate Backgrounding Diets

High-concentrate diets fed during backgrounding may be a viable alternative for some operations if properly managed. Protein deposition plateaus at approximately 1.0 kg ADG with medium-framed steers and coincides with maximal gains for backgrounding calves. Higher ADG would result in increased fat deposition. Ad libitum consumption of high-concentrate diets during this phase would result in relatively high ADG. Limiting dry matter intake (DMI) to provide energy levels adequate to support 1.0 kg ADG would alleviate problems with excessive subcutaneous fat deposition. Limiting intake has increased the percentage of dietary crude protein ruminally digested and depressed microbial efficiency and yield. These effects may ultimately lead to duodenal crude protein supplies inadequate to support estimated growth rates. Many Midwestern producers believe cattle must be allowed ad libitum intake during the winter for acceptable feedlot performance to occur. Ad libitum intake maximizes the heat of fermentation component and stabilizes ruminal conditions. Limit-feeding high concentrate diets results in rapid consumption of relatively large quantities of readily fermented feedstuffs. Lactate production with this situation may exceed the calf\u27s rumen buffering capabilities. Monensin supplementation may improve feedlot performance of cattle on limit-fed high-concentrate (LFHC) diets. When energy is limiting growth, monensin improves ADG, and when energy supplies are adequate or in excess, monensin improves feed efficiency. These effects were probably the result of decreased acetate propionate ratios. Monensin has been shown to inhibit bacterial proteolytic rates, yielding increased dietary crude protein bypass. Monensin has also been shown to effectively reduce lactate production. The combined effects of limit-feeding high concentrate diets and monensin cause uncertainty concerning optimal dietary crude protein levels. Monensin levels required to elicit ruminal responses resulting in optimal performance are also unclear. The objective of this research is to determine the optimal levels of dietary CP and monensin in LFHC diets as evaluated by backgrounding performance of steer calves