The effect of zilpaterol supplementation and RFI on growth performance

Abstract Text:

The effect of zilpaterol supplementation and RFI on growth performance

L. J. Walter*¹, T. J. McEvers¹, N. D. May¹, J. A. Reed¹, J. P. Hutcheson², and T. E. Lawrence¹

¹West Texas A&M University, Canyon, ² Merck Animal Health, Summit, NJ.

Supplementation of zilpaterol hydrochloride (ZH) impacts live cattle performance. Research has not focused on individual intake or the impact upon residual feed intake (RFI) when cattle are supplemented ZH. A 308 day serial-harvest trial was conducted in Holstein steers (n=110) blocked by 11 harvest dates (d252-534) and assigned to ZH or control treatments (n=5 per treatment per harvest). Individual DMI was collected using the GrowSafe system and rations were sampled monthly for proximate analysis (CP = 14.5±0.7; NE_m = 2.2±0.1 Mcal/kg; NE_g = 1.5±0.03 Mcal/kg). Every 28 days, DMI, ADG and SBW (BW*0.96) were calculated. Within each 28 day period, prior to ZH supplementation, RFI was calculated for each steer with a regression equation (coefficients of metabolic BW and shrunk BW gain); steers were assigned to a high or low RFI. Statistical analysis for data generated prior to ZH supplementation was conducted using a mixed model with fixed effects of RFI and days on feed (DOF) and random effects of harvest group and head count per feeding node; DOF was a repeated measure. Analysis of data during the ZH supplementation period was conducted using a mixed model with the fixed effects of ZH, DOF, and RFI and the random effect of harvest group. Intake prior to ZH supplementation was associated with RFI (P<0.01); the high group consumed more DM than the low group (10.7 vs. 9.4 kg). A quadratic relationship between DMI and DOF was observed (P<0.01); an inflection point occurred at day 392. Gain efficiency (G:F) was also influenced (P<0.01) by RFI; steers in the high RFI exhibited a G:F of 0.13 whereas low RFI steers were 0.15. As DOF increased, ADG and G:F exhibited a linear decrease (P<0.01). During the ZH supplementation period, steers of the high RFI consumed more DM (P<0.01; 10.6 vs. 9.5 kg) than those of the low RFI. However, steers supplemented ZH consumed less (P=0.03) DM (9.7 vs. 10.3 kg).  No ZH x RFI interaction (P=0.42) was observed for DMI.  Daily gain was not different (P≥0.22) between ZH treatments or RFI group. However, G:F tended (P=0.07) to be greater for steers supplemented ZH; RFI did not affect G:F (P=0.39).  

Keywords:

DMI, RFI, zilpaterol