Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 27, 1998
Publication Date: N/A
Interpretive Summary: Eighty to ninety percent of the protein-nitrogen fed to beef cattle is subsequently excreted in the feces and urine. In the feedlot, much of this excreted nitrogen can be converted to ammonia by soil and fecal bacteria and lost to the atmosphere. This loss of nitrogen not only contributes to concerns about odor, but also lessens the fertilizer value of the manure collected from feedlot pens since it decreases the nitrogen content of the manure and increases the nitrogen:phosphorus ratio of the manure. If animals retained more of the nitrogen (i.e. Protein) they were fed, it would lead to decreased requirements for protein in the diet and to decreased amounts of nitrogen that could potentially pollute the air and/or water. This research was conducted to determine if the animals metabolic system could be adjusted to increase the efficiency of nitrogen utilization and thus decrease the amounts of nitrogen required in the diet. Sheep were efed diets that contained deficient (10%), marginally adequate (12.5%) or above adequate (15%) concentrations of crude protein. Other animals were fed the deficient and above adequate diets at 24-h or 48-h intervals. In the first experiment, oscillating the dietary protein concentration at 48-h intervals increased nitrogen retention but in the second experiment, it did not. This was probably due to differences in the proteins fed in the two diets. These results suggest that protein requirements of ruminants may be decreased via oscillating dietary protein concentrations. However, additional research is need to confirm these results and/or to determine the optimal regimens to use under practical conditions.
Technical Abstract: Nitrogen excreted by beef cattle can be lost by volatilization to the atmosphere, lost by runoff and percolation or be retained in manure. Improving the retention of dietary N should decrease N losses to the environment. To this end, the effects of oscillating concentrations of dietary protein (CP) on nutrient retention was determined using lambs fed a a90% concentrate diet. Ten St. Croix lambs were used in two 5 x 5 Latin square experiments. Dietary treatments consisted of the following: 1) 10% CP, 2) 12.5% CP, 3) 15% CP, 4) 10% and 15% CP diets oscillated at 24-h intervals, and 5) 10% and 15% CP diets oscillated at 48-h intervals. Supplemental N was provided by cottonseed meal in Trial 1 and by a 50:50 (N basis) blend of cottonseed meal:urea in Trial 2. Nitrogen retention increased linearly (P < .01) with increasing N intake in both trials (.77, 1.33, and 1.89 g/d for 10, 12.5, and 15%, respectively in Trial 1; .94, 1.78, and 2.19 g/d for 10, 12.5, and 15%, respectively in Trial 2). Compared to continuously feeding the 12.5% CP diet, oscillating the 10 and 15% CP diets on a 24-h basis did not significantly affect N retention in either trial. Oscillating dietary CP at 48-h intervals did not affect N retention in Trial 2 (1.82 g/d) but increased (P < .05) N retention by 38% in Trial 1 (1.87 g/d). Phosphorus, K, and Na excretion were not affected by dietary treatments in Trial 1. In Trial 2, P retention increased (linear, P < .05) with increasing dietary CP and was greater (P < .05) by lambs on the 48-h oscillation treatment than by lambs fed the 12.5% CP diet. These results suggest that oscillating dietary CP concentration might potentially improve utilization of N by ruminants fed high-concentrate diets.