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Effects of Source and Level of Added Zinc on Muscle Fiber Diameter and Skeletal Muscle Protein Turnover of Finishing Pigs Fed Ractopamine HCl

Wednesday, March 19, 2014
Grand Ballroom - Posters (Community Choice Credit Union Convention Center)
Chad B. Paulk , Kansas State University, Manhattan, KS
Mike D. Tokach , Kansas State University, Manhattan, KS
Jim L. Nelssen , Kansas State University, Manhattan, KS
Derris D Burnett , Kansas State University, Manhattan, KS
Mathew A Vaughn , Kansas State University, Manhattan, KS
Kelsey J Phelps , Kansas State University, Manhattan, KS
Steve S. Dritz , Kansas State University, Manhattan, KS
Joel M. DeRouchey , Kansas State University, Manhattan, KS
Robert D. Goodband , Kansas State University, Manhattan, KS
Terry A. Houser , Kansas State University, Manhattan, KS
Keith D Haydon , Elanco Animal Health, Greenfield, IN
John M. Gonzalez , Kansas State University, Manhattan, KS
Abstract Text:

A total of 320 pigs (PIC 327 × 1050, 98 kg BW) were used in a 35-d study to determine the effects of supplemental Zn on muscle fiber cross-sectional area (CSA) and muscle specific relative gene expression of finishing pigs fed ractopamine-HCl (RAC; Elanco Animal Health, Greenfield, IN).  Pens were randomly allotted to diets with 2 pigs per pen. Treatments (n=8) were a corn-soybean meal control diet (0.66% SID Lys), a diet (0.92% SID Lys) with 10 ppm RAC, the RAC diet plus 75, 150, and 225 ppm added Zn from ZnO or Availa-Zn (Zinpro, Eden Prairie, MN). All diets contained 55 ppm Zn from ZnSO4. One pig was randomly selected from 16 pens per treatment for collection of Longissimus lumborum muscle biopsies on d 0, 8, 18, and 32.  Pigs fed the RAC diets had increased (P=0.05) CSA of type IIA fibers and a trend for increased (P=0.10) type IIX CSA.  Pigs fed RAC diets with added Zn tended to have increased (quadratic, P=0.10) type IIB fiber CSA.  There were no treatment effects on number of fiber associated nuclei (P>0.10). Pigs fed RAC diets had increased (P=0.06) relative expression of IGF-1 on d 8 compared to those fed the control diet, but there were no differences on d 18 and 32 (P>0.10). Relative expression of IGF-1 decreased (quadratic, P<0.04) with increasing levels of Zn on d 8 and 18.   There was no difference in IGF-1 receptor (IGF-1R) expression (P>0.10) between pigs fed the control and RAC diets.  Pigs fed diets with increasing levels of Zn had a tendency for decreased (quadratic, P<0.08) relative expression of IGF-1R on d 18. Pigs fed RAC diets had increased relative expression of Pax7 on d18 (P<0.04) and a tendency for increased (P<0.08) expression on d 8 and 32; however, there was no response in the relative expression of Myf5, MyoD, and Myogenin.  Pigs fed increasing levels of added Zn had a tendency for increased (linear, P<0.10) relative expression of Pax7 on d 8 and 18; however, there was no response in the relative expression of Myf5, MyoD, and Myogenin.  Therefore, RAC-stimulated hypertrophy occurred independent of satellite differentiation.  Additional Zn did not dramatically increase muscle fiber CSA, possibly due to a reduction of muscle IGF-1 and IGF-1R mRNA expression caused by the Zn.  

Keywords: IGF-1, ractopamine-HCl, zinc