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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Livestock Nutrient Management Research » Research » Publications at this Location » Publication #190552
Title: EFFECTS OF PHASE FEEDING OF PROTEIN ON PERFORMANCE, BLOOD UREA NITROGEN CONCENTRATION, MANURE N:P RATIO AND CARCASS CHARACTERISTICS OF FEEDLOT CATTLE

Author
item VASCONCELOS, J - TAES
item GREENE, L - TAES
item Cole, Noel
item BROWN, M - WTAMU
item MCCOLLUM, F - TCE
item TEDESCHI, L - TAMU

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2006
Publication Date: 9/15/2006
Citation: Vasconcelos, J.R., Greene, L.W., Cole, N.A., Brown, M.S., McCollum, F.T., Tedeschi, L. 2006. Effects of phase feeding of protein on performance, blood urea nitrogen concentration, manure n:p ratio and carcass characteristics of feedlot cattle. Journal of Animal Science. 84:3032-3038.

Interpretive Summary: As beef cattle mature, their protein requirements (as a percent of diet dry matter) decrease. By decreasing the dietary protein concentration late in the feeding period it may be possible to decrease nitrogen inputs, costs of gain, and ammonia losses without adversely affecting animal performance. Therefore, we conducted two experiments to determine the effects of phase feeding of crude protein (CP) on performance, blood urea nitrogen (BUN), manure N:P ratio, and carcass characteristics of steers fed in a feedlot. In experiment 1, 45 crossbred steers (BW = 423 kg) were individually fed a diet formulated to contain 13% CP (DM basis) for 62 d. On d 62, the dietary CP was either maintained at 13% or changed to contain 11.5% or 10% CP until harvest. Reducing the CP concentration of the diet did not affect average daily gain of steers from d 62 to 109 nor over the 109-d feeding period (1.45, 1.50 and 1.49 kg/d for 13%, 11.5%, and 10% CP, respectively). No differences between treatments were detected for BUN concentrations, gain:feed, dry matter intake, and carcass characteristics. In experiment 2, two trials were conducted using 204 (BW = 406 kg) and 162 (BW = 342 kg) crossbred steers housed in 21 and 18 pens in summer and winter, respectively. Data from trials 1 and 2 were pooled for statistical analysis. Steers were fed a diet formulated to contain 13% CP until the weighted approximately 477 kg; then diets were either maintained at 13% CP or reduced to contain 11.5 or 10% CP. Reducing the CP content of the diet did not affect ADG after the diet change, or throughout the finishing period. Steers fed the 13% CP diet had greater BUN concentrations than steers fed the 11.5 and 10% CP diets. Pen surface manure had different N:P ratios (3.70, 3.72, and 3.96 for the 13% CP, 11.5% and 10% CP diets, respectively). Carcasses from cattle fed 11.5% CP diet had greater fat thickness, whereas carcasses from cattle fed 13% CP had a higher marbling score than steers fed the 11.5% or 10% CP diets. Other carcass characteristics, DMI, G:F, and manure composition did not differ among treatments. These results indicated that reducing crude protein concentration during the final 48-56 days of the finishing period does not adversely affect feedlot performance but can improve the N and P relationship in the manure.

Technical Abstract: Two randomized complete block design experiments were conducted to determine the effects of phase feeding of crude protein on performance, blood urea nitrogen (BUN), manure N:P ratio, and carcass characteristics of steers fed in a feedlot. In experiment 1, 45 crossbred steers (BW=423 kg) were individually fed a diet formulated to contain 13% CP (DM basis) for 62 d. On d 62, the dietary CP was maintained at 13% or formulated to contain 11.5% or 10% CP until harvest. Actual CP values were 12.75, 11.8 and 9.85%, respectively. Reducing the CP concentration of the diet did not affect (P = 0.54) ADG of steers from d 62 to 109 nor over the 109-d feeding period (1.45, 1.50 and 1.49 kg/d for 13%, 11.5%, and 10% CP, respectively; P = 0.85). No differences between treatments were detected for BUN concentrations on d 0, 62, and 109 (P = 0.65, P = 0.49, and P = 0.12, respectively). Gain:feed, DMI, and carcass characteristics did not differ among treatments (P > 0.10). In experiment 2, two trials were conducted using 204 (BW = 406 kg) and 162 (BW = 342 kg) crossbred steers housed in 21 and 18 pens (9 to 10 head/pen) during summer and winter in two trials, respectively. Data from trials 1 and 2 were pooled for statistical analysis and trial effect was added to the statistical model. Steers were fed a diet formulated to contain 13% CP until reaching approximately 477 kg. When pen average weight was 477 kg, diets were either maintained at 13% CP or reduced to contain 11.5 or 10% CP. Actual CP values were 12.3, 11.48, and 9.3% CP for treatments 13, 11.5, and 10%, respectively. Reducing the CP content of the diet did not affect ADG after the diet change (P = 0.16) or throughout the finishing period (P = 0.14). Immediately before the harvest, steers fed the 13% CP diet had greater (P < 0.001) BUN concentrations than steers fed the 11.5 and 10% CP diets. Pen surface manure had different (P = 0.024) N:P ratios (3.70, 3.72, 3.96 for the 13% CP, 11.5% and 10% CP diets, respectively). Carcasses from cattle fed 11.5% CP diet had greater fat thickness (P = 0.021), whereas carcasses from cattle fed 13% CP had a higher marbling score (P= 0.004) than steers fed the 11.5% or 10% CP diets. Other carcass characteristics, DMI, G:F, and manure composition did not differ (P > 0.10) among treatments. These results indicated that reduced CP concentration during the finishing period does not affect feedlot performance but can improve the N and P relationship in the manure.