| Abstrakt: |
Crossbred harrows (n = 144; 80 kg) from four farrowing groups were phenotypically selected intc fat (FAT) and lean (LEAN) pens using ultrasound. The difference in 10th-rib fat depth between the LEAN and FAT groups was ≥0.5 cm. Within a farrowing group! pigs were assigned to pens (five pigs per pen and eight pens per phenotype) to equalize pen weight and fat depth. Pigs were fed a corn-soybean meal diet con taming 19% CP, 1.0% added animal/vegetable fat, and 1.1% lysine (as-fed basis). Half the pens received 10 ppm (as-fed basis) of ractopamine (RAG) during the 28-d finishing phase. At 7-d intervals, live weight and feed disappearance were recorded to calculate ADG, ADFI, and G:F, and 10th-rib fat depth and LM area were ultrasonically measured to calculate fat-free lean and fat and muscle accretion rates. During the first 7 d or feed, LEAN pigs fed RAG gained less (P < 0.05) thar FAT pigs fed RAG or LEAN and FAT pigs fed the control diet (RAG x phenotype; P = 0.02); however, RAC did not (F > 0.25) affect ADG after the second, third, and fourth weeks, or over the entire 28-d feeding period! Although wk-2 and -3 ADG were higher (P ≤ 0.03) in LEAN than in FAT pigs, phenotype did not (P = 0.08) affect overall ADG. Dietary RAG decreased (P ≤ 0.05) ADFI over the 28-d feeding trial, as well as in wk 2, 3, and 4, but intake was not (P > 0.20) affected by phenotype. Neither RAG nor phenotype affected (F > 0.10) G:F after 7 d on trial; however, RAG improved (P ≤ 0.04) wk-3, wk-4, and overall G:F. Lean pigs were more efficient (P ≤ 0.05) in wk 2 and 3 and over the duration of the trial than FAT pigs. Ultrasound LM accretion (ULA) was not (P ≥ 0.10) affected by RAG; however, LEAN pigs had greater (P ≤ 0.02) ULA in wk 2 and 4 than FAT pigs. Although fat depth was lower (P < 0.01) in RAC-fed pigs than pigs fed the control diet, ultrasound fat accretion rate indicated that RAG-pigs deposited less (P = 0.04) fat only during wk 4. In addition, calculated fat-free lean (using ultrasound body fat, ULA, and BW) was increased (P < 0.05) in RAG pigs after 3 and 4 wk of supplementation. In conclusion, RAC enhanced the performance of finishing swine through decreased ADFI and increased G:F, whereas carcass lean was enhanced through decreases in carcass fat and increases in carcass muscling. [ABSTRACT FROM AUTHOR] |
