Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 20, 2004
Publication Date: July 26, 2004
Citation: Archibeque, S.L., Freetly, H.C., Cole, N.A., Ferrell, C.L. 2004. Oscillating protein concentrations of finishing beef cattle diets improves nitrogen retention by improving nitrogen digestibility [abstract]. Journal of Animal Science 82(Suppl. 1):116. Technical Abstract: We hypothesized that oscillating dietary CP concentrations would improve N efficiency and thus decrease overall N requirements and minimize contribution of nutrients to environmental systems. Eight Charolais-cross steers (358 kg BW) were used in a replicated 4x4 Latin Square design. The steers were allowed ad libitum access to the following diets: 1) Low (Lo; 9.1% CP), 2) Med (11.8% CP), 3) High (Hi; 13.9% CP), or 4) Lo and Hi diets oscillated on a 48 h interval (Osc). Dry matter intake did not differ between treatments (P>0.05), but nitrogen intake varied (P<0.01) from 94 (Lo) to 131 (Med), 142 (Hi), and 133 g/d (Osc). Dry matter digestibility increased (P<0.01) from 71.8 (Lo) to 75.8 (Med), 77.7 (Hi), and 77.5 % (Osc). Nitrogen digestibility increased (P<0.01) from 62.2% (Lo) to 67.2 (Med), to 70.9 (Osc) and 70.1 (Hi). Nitrogen retention was greater (P<0.01) in the steers fed the Osc diet (55.0 g/d) than either the steers fed the Lo (34.8 g/d) or Hi (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 Lo diet. Urinary urea N was not different (P>0.10) between steers fed either the Med (19.5 g/d) or Osc (21.3 g/d) diet. Similarly, urinary urea as a percentage of total urinary N did not differ (P>0.10) between steers fed the Med (48.4) and Osc (51.5%) diets. Daily heat production tended (P<0.09) to be less for the steers fed the Lo (177) diet than those fed the Med (189), Hi (188), or Osc (182 kcal/BW0.75) diets. These data indicate that oscillating dietary protein will improve the N retention of finishing steers compared to those in both excessive and deficient N states, while steers fed a similar daily concentration of dietary N in a static form only improved N retention compared to steers deficient in dietary N. Digestive mechanisms may play a greater role in this improvement in N retention than endogenous handling of nonprotein N.