Effects of Feeding a Finisher Feed Containing Ractopamine HCl to Pigs Sorted By Body Weight at Placement on Growing-Finishing Pig Growth Performance

Our objective was to determine the effects of feeding left over finisher diet containing ractopamine HCl (RAC) and 0.82% standardized ileal digestible (SID) Lys to grower pigs of different BW at placement in the finisher. A total of 1,188 pigs (PIC 359×1050; initially 16.6±0.16 kg) were used in a 72-d study. Pens of pigs were blocked by location and randomly allotted to 1 of 6 treatments. Treatments included three BW categories: light (12.0±0.27 kg), medium (15.9±0.38 kg), and heavy (21.9±0.55 kg); and two dietary strategies: standard grow-finisher diets throughout (Control) or 4.5 kg/pig of a late finishing feed containing 5 mg/kg RAC and 0.82% SID Lys fed at placement and then standard diets thereafter. There were 7 pens per treatment and 27 pigs per pen. Dietary strategy, BW category, and their interaction were included as fixed effects in the statistical model and location block as a random effect. An interaction (P<0.03) between BW and diet occurred for ADG and G:F from d 0-15. Pigs fed the finisher diet with RAC had reduced ADG and G:F within all three BW categories. However, the decrease was greater in the medium BW than the other two BW categories. Pigs fed the finisher diet with RAC had reduced ADFI compared to pigs fed the control (P<0.001) from d 0-15. Overall, ADG, ADFI, and G:F differed between the BW categories (P<0.001), with heavy pigs having greater ADG and ADFI, and poorer G:F. Pigs fed the 4.5 kg/pig of finisher diet with RAC had reduced growth rate (761 vs 784 g/d; P<0.001) and feed intake (1.61 vs 1.65 kg/d; P<0.005), but no evidence for differences were observed for G:F. In conclusion, feeding a finishing diet containing ractopamine during the early stages of the grower period reduced growth performance regardless of BW category due to a decrease in feed intake compared to pigs fed standard grow-finisher diets. This demonstrates that bins holding a finisher diet containing RAC and 0.82% SID Lys should be emptied prior to placement of the next group of pigs.

	Light		Medium		Heavy
Item	Control	RAC	Control	RAC	Control	RAC	SEM
d 0 to 15
ADG , g1	572d	499e	640c	544d	744a	689b	6.8
ADFI, g2	807	740	916	866	1,202	1,175	10.9
G:F, g/kg3	709c	674c	699c	628b	619b	586a	7.3
1 Diet x BW: P=0.018; 2 Diet: P<0.001, BW: P<0.001; 3 Diet x BW: P=0.026.