ARS | Publication request: Effects of Phase Feeding of Protein on Performance, Blood Urea Nitrogen, and Carcass Characteristics of Finishing Beef Cattle: Ii. Group Fed Steers

Submitted to: Beef Cattle Research In Texas
Publication Acceptance Date: July 22, 2004
Publication Date: August 4, 2004
Citation: Vasconcelos, J.T., Greene, L.W., Cole, N.A., Mccollum, F.T. 2004. Effects Of Phase Feeding Of Protein On Performance, Blood Urea Nitrogen, And Carcass Characteristics Of Finishing Beef Cattle: Ii. Group Fed Steers. Beef Cattle Research In Texas. P. 135-139

Interpretive Summary: Over the past 30 years cattle feedlots have increased in size leading to greater concentrate of manure and the nutrients within the manure. Consequently, feed nutrients such as N, P and trace minerals are being concentrated in relatively small geographic areas. Because of changes in growth rate and body composition, requirements for metabolizable protein change during the finishing period. However, feedlot cattle are usually fed one common diet with a constant level of crude protein from about d 24 until they are harvested. Consequently, protein may be underfed early in the feeding period and overfed late in the feeding period. The question becomes, whether nutrient excretion can be reduced without negatively impacting animal performance. The objective of this study was to determine the effects of decreasing dietary protein concentration late in the feeding period (ie. phase feeding) on performance, blood urea nitrogen concentration, and carcass characteristics of group-fed finishing steers. One hundred eighty four steers (BW = 897 lb) were fed three protein strategies: 1) a 13% crude protein finishing diet for 120 days,2) 13% protein for 62 then reduced to 11.5% for 56 days, or 3) 13% protein for 62 days then 10% protein for the last 56 days. Reducing the CP content of the diet did not adversely affect performance or carcass characteristics of steers. These data suggest that dietary protein levels can be reduced to conserve nitrogen during the final stages of finishing without any reduction in animal performance.

Technical Abstract: One hundred eighty four steers (BW = 897 lb) were fed a 13% CP finishing diet until reaching 1,050 lb, when their diets were either maintained at 13% CP or reduced to 11.5% CP or to 10% CP. Reducing the CP content of the diet did not affect ADG after the diet change (P = 0.21) or throughout the finishing period (P = 0.09). Immediately before the harvest, steers fed the 13% CP diet had greater (P < 0.0001) blood urea N concentration (9.84 mg/dL) than animals fed the 11.5 % and 10% CP diets (7.02 and 4.75 mg/dL). Manure obtained from pen surface had different (P = 0.038) N:P ratios (3.87, 3.45, 3.56 for the 10% CP, 11.5% and 13.0% CP diets, respectively). Carcass characteristics, DMI, feed efficiency, and manure composition did not differ among treatments (P > 0.10). Data indicate that reducing CP levels during the finishing period does not affect feedlot performance.