Manure Concentration of N:P, Animal Performance, and Blood Urea Nitrogen Concentrations of Feedlot Steers Phase Fed Diff

1. Manure Concentration of N:P, Animal Performance, and Blood Urea Nitrogen Concentrations of Feedlot Steers Phase Fed Different Levels of Protein. L.W. Greene1, 2 and J. T. Vasconcelos1,3 1Texas Agricultural Experiment Station - Amarillo2West Texas A&M University, Canyon 3Texas A&M University

2. Introduction • Cattle are started on high concentrate finish diets at approximately 750 lbs and fed to an average weight of 1250 lbs. • Early in the feeding period, cattle have a greater deposition of lean tissue and less deposition of fat compared to later in the feeding period. • As animals mature through the feeding period, the composition of gain changes -- protein gain decreases and fat gain increases in relative proportion.

3. Introduction • The typical feedlot diet in the Southern Plains contains 13.0 to 13.5% Crude Protein (% N X 6.25)

4. Average excess = 50 g/d Crude protein excess or deficiency (g/d) during feeding period given a typical diet (adapted from Galyean) Days on Feed Days on Feed

5. Nitrogen retained, % of intake % Collection Period

6. Introduction • The typical feedlot diet in the Southern Plains contains approximately 0.33% P • The typical feedlot steer requirement for P is likely < 0.18%.

7. Average excess 6.7 g/d Phosphorus excess or deficiency (g/d) during feeding period given a typical diet (adapted from Galyean) Days on Feed

8. Phosphorus retained, % of intake % Collection Period

9. Introduction Source Crude Protein, % Phosphorus, % Corn grain 9.8 0.31 Corn silage 9.0 0.27 Sorghum silage 11.0 0.25 Alfalfa hay 22.0 0.30 Cottonseed meal 46.0 0.93 Dried distillers grains 28.0 0.90+ • The typical feedlot diet does not contain supplemented P. • The dietary P is supplied from the dietary ingredients.

10. Objective • Determine the effects of phase-feeding of protein in finishing steers on • Steer performance • Blood urea nitrogen concentration • Manure N concentration • Manure P concentration • Carcass characteristics

11. Methods One hundred eighty four steers Randomized block design (blocked by weight into heavy medium and light and by start date) 54 steers started on June 6, 2003 130 steers started on June 17, 2003 Steers were housed in 21 pens (7 pens/treatment)

12. Methods Three dietary treatments 1. Control diet – 13% Crude protein diet fed continually throughout the feeding period 2. 11.5% Crude protein – 13% Crude protein diet fed until cattle the average of the block reached 477 kg, then switched to an 11.5% crude protein diet 3. 10.0% Crude protein – 13% Crude protein diet fed until cattle the average of the block reached 477 kg, then switched to no supplemental crude protein diet

13. Methods The supplemental protein was supplied from equal amounts of nitrogen from urea and cottonseed meal

14. Methods Ingredient composition of finishing diets (DM basis)

15. Methods Analyzed chemical composition of finishing diets.

16. Average Daily Gain P-value =0.912 Beginning until diet change kg/d

17. Average Daily Gain P-value =0.213 Diet change until finish kg/d

18. Average Daily Gain P-value =0.094 Beginning until finish kg/d

19. Dry matter intake P-value =0.619 Beginning until diet change kg/d

20. Dry matter intake P-value =0.008 Diet change until finish kg/d

21. Dry matter intake P-value =0.056 Beginning until finish kg/d

22. Gain efficiency P-value =0.832 Beginning until diet change Kg gain/ Kg intake

23. Gain efficiency P-value =0.294 Diet change until finish Kg gain/ Kg intake

24. Gain efficiency P-value =0.094 Beginning until finish Kg gain/ Kg intake

25. Plasma Urea Nitrogen (mg/dL) P-value =0.8100 P-value =0.0001 P-value =0.8280 Day 0 Diet change Harvest

26. Pen surface manure concentration P-value =0.600 Nitrogen %

27. Pen surface manure concentration P-value =0.931 Ammonia Nitrogen %

28. Pen surface manure concentration P-value =0.549 Organic Nitrogen %

29. Pen surface manure concentration P-value =0.642 Phosphorus %

30. Pen surface manure concentration P-value =0.038 Nitrogen:Phosphorus

31. Carcass Characteristics P-value =0.227 Fat thickness, cm

32. Carcass Characteristics P-value =0.192 Longissimus area, cm2

33. Carcass Characteristics P-value =0.459 Kidney, Pelvic and Heart Fat, %

34. Carcass Characteristics P-value =0.663 Hot carcass wt, kg

35. Carcass Characteristics P-value =0.763 Live weight, kg

36. Carcass Characteristics P-value =0.874 Dressing percentage, %

37. Carcass Characteristics P-value =0.173 Marbling score

38. Carcass Characteristics P-value =0.174 Yield grade

39. Summary • Variation of crude protein in the experimental diet resulted in lower than expected crude protein intake. • Reducing crude protein intake to 8.3% reduced feed intake and tended to reduce ADG when summarized across the entire feeding period. • No differences were detected in manure nutrient concentrations but the N:P ratio was increased when the lower CP diet was fed. • No differences were detected in USDA Carcass Characteristics.