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Nitrogen losses from outdoor feedlots are an important environmental issue facing beef producers. Two methods that may lower N losses are cleaning pens more frequently to prevent exposure of manure N during collection on pen surfaces or increasing the C:N ratio of manure by increasing organic matter (OM) on the pen surface. Feeding diets lower in OM digestibility or directly adding OM to pen surfaces may increase the C:N ratio and decrease N losses. In Exp. 1, calves in the winter/spring or yearlings in the summer were fed diets lower in digestibility (BRAN) or fed in pens with sawdust additions (SAWDUST) to increase the C:N ratio and OM on the pen surface. These two treatments were compared to conventional feeding and pen management systems (CONTROL). While decreasing digestibility did depress performance as measured by feed efficiency, feeding BRAN did increase OM on the pen surface and decreased N losses compared to CONTROL in the winter/spring but did not affect N losses or increase manure N during the summer. Adding SAWDUST directly to pens yielded similar results to BRAN, with decreased losses in the winter/spring and little effect during the summer compared to CONTROL. However, when manure was composted, N recovery during composting was increased for both the BRAN and SAWDUST treatments compared to CONTROL suggesting that OM may decrease N losses when manure is composted. In Exp. 2, diets similar to CONTROL and BRAN were evaluated as a 2 X 2 factorial treatment design experiment. The other factor evaluated was cleaning frequency. Pens were either cleaned monthly or cleaned once at the end of the winter/spring feeding period. Performance of steers was similar to results in Exp. 1, with lower feed efficiency for cattle fed BRAN compared to the CONTROL treatment. Dietary treatment and cleaning frequency treatments interacted for N balance in the feedlot. Nitrogen losses were decreased and manure N increased for cattle fed BRAN compared to CONTROL if pens were clean monthly. If pens were not cleaned until the end of the feeding period, diet had little effect on N losses. Interestingly, N losses were similar between both cleaning frequency treatments for cattle fed CONTROL. In Exp. 3, 54 pens were used to evaluate the impact of monthly cleaning on N removal in manure during the summer months. The same diet was fed in all pens, resulting in similar performance across treatments. Cleaning pens monthly increased the amount of manure N removed per steer by 3.74 kg or 66.2% compared to pens cleaned once at the end of the feeding period. These data suggest that cleaning pens more frequently and adding OM to pen surfaces or compost may decrease N losses from outdoor feedlot pens. Treatment responses appear to be dependent on ambient temperature or season, suggesting that future research needs to address both summer and winter/spring feeding periods typical of beef cattle operations. |
