A. Bouvet, L. Ruhnke and P.K. Basrur. Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario (Bouvet, Basrur) and Mycoplasma Laboratory, Veterinary Laboratory Services, Ontario Ministry of Agriculture and Food, Guelph, Ontario (Ruhnke).

A fragile site has been noted on the long arm of one of the X chromosomes in metaphase spreads of cultured blood from heifers afflicted with Baldy Calf Syndrome. This would suggest a direct association between the Baldy Calf Syndrome and the presence of the Fragile X. However, the skin lesions commonly seen in baldy calves are infected with Mycoplasma arginini and it is known that non-fermenting Mycoplasma spp. depleting the culture medium of arginine will induce chromosome breakage in human lymphocytes.

In order to determine whether Mycoplasma arginini isolated from the skin lesions of baldy calves would induce or augment the incidence of fragile sites similar to those noted in cultures of lymphocytes from baldy calves, cultures of blood samples from six normal Holstein-Friesian heifers were inoculated with Mycoplasma arginini compared to those in inoculated cultures. However, there was no significant increase in the percentage of metaphase spreads showing breakage on the X chromosomes in infected cultures.

The results of this study suggest that the Fragile X noted in lymphocyte cultures from baldy calves may not be elicited by Mycoplasma arginini infection, but may be a pleiotropic effect of the mutant gene for Baldy Calf Syndrome. The presence of autosome gaps and breaks in culture infected with Mycoplasma arainini could be correlated with the trend noted in previous studies that the frequency of autosome] alterations increases in cultures of skin collected from baldy calves as the condition progresses.

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