Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2007
Publication Date: 6/1/2007
Citation: Archibeque, S.L., Freetly, H.C., Cole, N.A., Ferrell, C.L. 2007. The influence of oscillating dietary protein concentrations on finishing cattle. II. Nutrient retention and ammonia emissions. Journal of Animal Science. 85(6):1496-1503. Interpretive Summary: It has been suggested that oscillating dietary protein concentrations will improve nitrogen usage by finishing cattle as a method of minimizing environmental impacts. Reduced nitrogen excretion results in less potential for the production of ammonia, which is labile and has undesirable environmental impacts/implications. The present study indicates that the reduction in ammonia emissions caused by oscillating dietary protein are smaller than the impact of simply feeding lower protein diets. However, steers fed oscillating protein have a higher level of productivity than those fed the lower protein diets.
Technical Abstract: We hypothesized that oscillating dietary CP concentrations would improve efficiency of N use and reduce N loss to the environment. Charolais cross steers (n = 8; 315 +/- 21 kg BW) were used in a replicated 4 x 4 Latin Square design. The steers were allowed ad libitum access to the following diets: 1) Low (9.1% CP), 2) Medium (Med; 11.8% CP), 3) High (13.9% CP), or 4) Low and High diets oscillated on a 48 h interval (Osc). Dry matter intake did not differ among treatments (P = 0.46), but N intake differed (P < 0.01) from 94 (Low) to 131 (Med), 142 (High), and 133 g/d (Osc), as designed. Dry matter digestibility increased (P < 0.01) from 71.8 (Low) to 75.8 (Med), 77.7 (High), and 77.5% (Osc). Nitrogen digestibility increased (P < 0.01) from 62.2 (Low) to 67.2 (Med) to 70.1% (High) and 70.9 (Osc). Nitrogen retention was greater (P < 0.01) in steers fed the Osc diet (55.0 g/d) than either the steers fed the Low (34.8 g/d) or High (40.2 g/d) diets. However, N retention of steers fed the Med diet (49.8 g/d) differed (P = 0.02) only from the steers fed the Low diet. Urinary urea N did not differ between steers fed either the Med (19.5 g/d) or Osc (21.3 g/d) diet, but was lower (P < 0.01) for those fed Low (8.2 g/d) and greatest for those fed High (39.2 g/d). Daily heat production (kcal/BW0.75) tended (P = 0.09) to be less for the steers fed the Low (177) diet than those fed the Med (189), High (188), or Osc (182) diets. Cumulative in vitro ammonia volatilization from the manure of steers fed the Osc diet was lower (P < 0.01) for the initial 5 d of incubation than those fed the Med diet, yet there was no difference after 11 d of incubation. Additionally, there was a decrease (P < 0.01) in in vitro ammonia volatilization as protein concentration in the diet decreased from High to Med to Low. These data indicate that oscillating dietary protein improved N retention of finishing steers compared to those in both high and low N diets and that these changes were great enough to similarly alter ammonia volatilization from manure.