Ammonia emissions and performance of backgrounding and finishing beef feedlot cattle fed barley-based diets varying in dietary crude protein concentration and rumen degradability.

Koenig, K.M., McGinn, S.M., and Beauchemin, K.A. (2013). "Ammonia emissions and performance of backgrounding and finishing beef feedlot cattle fed barley-based diets varying in dietary crude protein concentration and rumen degradability.", Journal of Animal Science, 91(5), pp. 2278-2294. doi : 10.2527/jas2012-5651  Access to full text

Abstract

Crossbred beef steers (n = 312) were used in an experiment with a completely randomized design during the growing (235 ± 1.6 kg initial BW) and finishing (363 ± 2.7 kg) phase to determine the effects of dietary CP concentration and rumen degradability on NH3 -N emissions, growth performance, and carcass traits. Diets were barley based and consisted of 55% silage and 45% concentrate in the backgrounding phase and 9% silage and 91% concentrate in the finishing phase. For each phase, there were 4 dietary treatments (6 pens of 13 cattle per diet): the basal diet with no protein supplementation (12% CP backgrounding and 12.6% CP finishing) or supplemented (14% CP) with urea (UREA), urea and canola meal (UREA+CM), or urea, corn gluten meal, and xylose-treated soybean meal (UREA+CGM+xSBM). Feed intake and BW of cattle were measured at 3-wk intervals. One pen of steers fed the 12 or 12.6% CP and 1 pen fed 1 of the 14% CP diets were housed in 2 isolated pens to quantify NH3 -N emissions using the integrated horizontal flux technique with passive NH3 samplers. In the backgrounding phase final BW, ADG, and G:F were less (P < 0.05) in cattle fed the 12% CP and UREA compared with the UREA+CM and UREA+CGM+xSBM diets. Nitrogen-use efficiency of cattle fed UREA+CM and UREA+CGM+xSBM was equal to that of cattle fed 12% CP and averaged 19.8%. In the finishing phase, there was no effect (P > 0.10) of CP supplementation on BW, DMI, ADG, G:F, N-use efficiency, and carcass traits. The NH3 -N emissions from December to February during the backgrounding phase ranged from 4.3 to 25.6 g N/(steer{bullet operator}d) and 3.8 to 16.3% of N intake and from April to July during the finishing phase ranged from 9.7 to 76.4 g N/(steer{bullet operator}d) and 4.4 to 26.7% of N intake. Differences in NH3 -N emissions between the pens of cattle fed the backgrounding diets with 12 and 14% CP were not detected. For cattle fed the 12.6 and 14% CP finishing diets, NH3 -N emissions tended (P ≤ 0.16) to be less for 2 of the 5 periods and averaged 14.4 and 28.1 g N/(steer{bullet operator}d) and 7.7 and 12.7% of N intake, respectively. The NH3 -N emitted as a % of N intake averaged 42% less for cattle fed 12.6% compared with 14% CP. Feeding the barley-based concentrate diet to finishing cattle with 12.6% compared with 14% CP diets reduced NH3 -N emissions with no effect on performance. Feeding the barley-based forage diet to backgrounding cattle with 12% CP, however, reduced performance compared with growing cattle fed supplementary degradable and undegradable true protein.

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