THE EFFECT OF MIXING STRESS ON THE INCIDENCE OF OSTEOCHONDROSIS IN PIGS: SCANNING ELECTRON MICROSCOPY

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Abstract
The object of this study was to determine the effect of mixing stress on the development of osteochondrosis, using scanning electron microscopy. Sixteen litters of eight pigs per litter were randomly assigned to one of four different treatment groups involving combinations of preweaning handling and postweaning mixing stress. Before weaning, all pigs were subjected to normal handling procedures, but one of the groups was handled with exceptional care. After-weaning treatments involved various amounts of mixing stress varying from no mixing to mixing every month. All pigs received standard starter, grower and finisher diets ad libitum (19, 16 and 14% crude protein, respectively). Eight pigs from each of the four treatment groups were randomly selected for slaughter at 3, 4, 5 and 6 mo of age. After slaughter elbow and knee joints were examined grossly and histologically by light and scanning electron microscopy for evidence of osteochondrosis. Handling and mixing stresses had no significant effect on performance in the grower or finisher periods. Mixing stress had no significant effect (P > 0.05) on the average lesion scores of cartilage from any of the sites studied. No differences were apparent under light microscopy in the morphology of humeral and femoral condylar cartilage of pigs from any of the treatment groups. Under scanning electron microscopy the surface of normal porcine condylar cartilage appeared very smooth with numerous clusters of chondrocytes evidenced by small protrusions from the surface. Pigs from the two mixed treatment groups showed extensive surface wear (osteoarthrosis) at the age of 6 mo. The results indicated that mixing stress had little effect on the incidence of osteochondrosis but may be involved in the progression of osteoarthrotic changes with advancing age. Key words: Scanning electron microscopy, swine, osteochondrosis, mixing stress

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