The influence of oscillating dietary protein concentrations on finishing cattle. I. Feedlot performance and odorous compound production

¹ USDA, ARS; US Meat Animal Research Center, Clay Center, NE 68933-0166

^* To whom correspondence should be addressed. E-mail: ferrell{at}email.marc.usda.gov.

	Abstract

We hypothesized that oscillating dietary CP concentration, which may improve N retention of finishing beef steers, would reduce manure odor compound production and total N inputs while yielding comparable performance. Charolais-sired steers (n = 144; 303 ± 5 kg initial BW) were used in a completely randomized block design (6 pens/treatment). The steers were fed to 567 kg on the following finishing diets based on dry-rolled corn: 1) LOW (9.1% CP), 2) Medium (MED; 11.8% CP), 3) HIGH (14.9% CP), or 4) LOW and HIGH oscillated on a 48-h interval for each feed (OSC). Steers fed LOW (7.80 kg/d) tended (P = 0.08) to have less DMI than steers fed either MED (8.60 kg/d) or OSC (8.67 kg/d), but not less than steers fed HIGH (8.12 kg/d). Daily N intake was greatest (P < 0.01) for steers fed HIGH (189 g), intermediate for MED (160 g) and OSC (164 g), and least for LOW (113 g). The ADG was lower (P < 0.01) for steers fed LOW (1.03 kg) than for those fed MED (1.45 kg), HIGH (1.45 kg), or OSC (1.43 kg). Similarly, steers fed LOW had a lower adjusted fat thickness (P < 0.01) and yield grade (P = 0.05), and tended (P = 0.10) to have less marbling than steers fed the other 3 diets. In slurries with feces, urine, soil, and water, incubated for 35 d, nonsoluble CP was similar among slurries from steers fed MED, HIGH, or OSC, but was less (P < 0.01) in slurries from steers fed LOW. However, throughout the incubation period, slurries from steers fed either HIGH or OSC had greater (P < 0.01) concentrations of total aromatics and ammonia than those from steers fed either LOW or MED. Also, the slurries from steers fed OSC had greater (P < 0.01) concentrations of branched-chain VFA than manure slurries from steers fed any of the other diets. These data indicate that although there is no apparent alteration in the performance of finishing steers fed diets with oscillating dietary protein, there may be undesirable increases in the production of compounds associated with malodor.

Key Words: beef steers, odor, protein oscillation

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