Effect of duration of limit feeding on nitrogen and phosphorus metabolism, growth performance, and carcass characteristics of Holstein × Zebu finishing steers

Objectives were to determine effects of the duration of limit feeding on nitrogen (N) and phosphorus (P) metabolism, growth performance, and carcass characteristics of finishing steers. Twenty-five Holstein × Zebu steers (average initial BW = 319 ± 16.2 kg; age = 19 ± 1.0 mo) were used. Five steers were slaughtered to provide baseline empty BW (EBW) and empty body composition (EBC) at d 0. Remaining steers were randomly allotted to 1 of 4 treatments: ad libitum-fed for 84 d (AL84); limit-fed (LF) for first 28 d (R28); LF for first 42 d (R42); and LF for 84 d (R84). During LF periods, steers fed R28, R42, and R84 were limit-fed to 85% of ad libitum based on AL84 steer DMI. All steers were fed 40% corn silage and 60% concentrate (DM basis) for 84 d. Total excretion of feces and urine were collected during 2 periods: d 25 to 27 (period 1), and d 73 to 75 (period 2). Nitrogen and P intake, urine and fecal excretions, and absorption and retention were quantified. Steers were weighed on d 1, 28, 42, and 84. The DMI, ADG, and G:F were evaluated during: d 1 to 28, d 29 to 42, and d 43 to 84. Individual EBW, EBC, and carcass characteristics were recorded. The DM, N, and P intakes were greater (P<0.01) for AL84 steers than R28, R42, and R84 steers when steers in R28, R42, and R84 treatments were LF. When transitioned to ad libitum feeding, R28 and R42 steers had similar (P>0.05) DM, N, and P intakes compared to AL84 steers. Fecal N and urinary P excretions did not differ (P≥0.40) among limit-fed and ad libitum-fed steers in either period. However, greater (P=0.02) fecal P excretions were observed in steers fed for ad libitum intake in period 2. The EBW, EBW gain (EBWG), whole body N retention, and P retention in period 1 and 2 were similar (P>0.05) in steers fed R28 and R42, in relation to AL84 steers. Steers fed R84 had the least (P<0.05) whole body N retention, EBW, and EBWG. Final BW, overall ADG, G:F, and HCW were not affected (P≥0.10) by treatment. Limit-feeding Holstein × Zebu steers for 84 days did not alter overall ADG, final BW, or carcass characteristics. Limit-feeding Holstein × Zebu steers can be used up to 42 days to reduce N and P excretion in feedlot, without impairing retention.