Effect of β-mannanase and Lysine Level During Ractopamine Feeding 35 Days Prior to Marketing on Growth Performance and Carcass Characteristics of Finishing Pigs

Abstract Text: Crossbred pigs (343) were blocked by ancestry, sex, and initial BW (97.3 kg) and allocated to mixed gender pens (5 or 6 pigs/pen) to 5 treatments with 10 or 12 pens/treatment. Dietary treatments included: 1) low lysine (0.80% SID Lys; LL); 2) LL+mannanase (0.08 MU/kg); 3) high lysine (0.95% SID Lys; HL); 4) HL+mannanase (0.08 MU/kg); 5) As treatment 3 + 3% CWG (CWG). Diets were corn-soy based (LL and HL=3335 and CWG=3517 kcal ME/kg) and contained 7.5 ppm ractopamine. One pig/pen was harvested on d 7 and 21, with remaining pigs harvested on d35. For d 0-7, 7-21, and 0-35 pigs fed the HL diets tended (P<0.10) to have greater G:F than pigs fed LL diets. For d 21-35 (P<0.09) and 0-35 (P<0.04) pigs fed LL diets had greater ADFI than pigs fed HL diets. Pigs fed enzyme had increased ADFI (P<0.05) d 21-28 and tended (P<0.10) to have improved ADG (984 vs 937 g/d) from d 21-35. For all time periods, pigs fed the CWG diet had greater G:F (P<0.02), during d 21-35 and 0-35 had greater ADG (P<0.04), and for periods 7-21 (P<0.01) and 0-35 (P<0.07) had reduced ADFI compared to pigs fed the HL diet. Pigs harvested on d 7 fed enzyme diets had increased (P<0.02) carcass yield and tended to have increased (P< 0.06) loin depth. Pigs fed LL diets had increased (P<0.05) backfat (BF) depth compared to pigs fed HL diets on d 7. Pigs fed HL diets harvested on d 21 had reduced (P<0.01) BF depth and increased (P<0.02) percent lean versus pigs fed LL diets, pigs fed CWG had increased (P<0.02) BF depth d 21 and d 35 and reduced (P<0.03) percent lean d 21 compared to pigs fed the HL diet. Overall, pigs fed HL diets had reduced (P<0.03) BF depth and increased (P<0.06) percent lean when compared to pigs fed LL and CWG diets.  In conclusion, pigs fed HL diets had reduced ADFI but improved G:F compared to pigs fed LL diets, which was further enhanced by addition of fat to treatment 3.  Pigs fed mannanase numerically improved growth rate by 5% and G:F by 3% the last 2 weeks of the study, with a greater response in the low lysine diets (ADG - 7.8% d 21-35, 3.1% overall, and G:F – 5.5% d 21-35), which may warrant further study in ractopamine diets.

Keywords: mannanase, lysine, ractopamine