ERYTHROCYTE FRAGILITY IN "DOUBLE-MUSCLED" CATTLE

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Abstract
Osmotic fragility of erythrocytes was determined on heparinized whole blood, sampled from a group of 95 cattle consisting of 73 normal animals from three breed groups and 22 animals showing varying degrees of the double-muscling (DM) trait. Four age groups and two sex groups were sampled from each breed group. Mean corpuscular fragility (MCF) values (the NaCl equivalence producing 50% hemolysis) were interpolated from a fragility curve derived for each animal. The DM breed group had significantly increased erythrocyte fragility as compared to the other breed groups. As animal age increased, the fragility of the erythrocytes was significantly decreased. Sex did not appear to influence erythrocyte fragility. Erythrocyte fragility was also related to the degree of phenotypic expression of the DM trait. Phenotypically extreme DM cattle had increased erythrocyte fragility as compared to phenotypically moderate- to normal-muscled animals of the DM group. Erythrocyte fragility in two of the other breed groups overlapped into the erythrocyte fragility range of the phenotypically moderate- to normal-muscled animals of the DM group, while the remaining breed group showed a decreased erythrocyte fragility. This overlapping provides adequate grounds for the rejection of the erythrocyte osmotic fragility test used in this study as a means of unequivocal identification of DM carriers in cattle. Despite the rejection of this test as a means of carrier detection, the suggestion that DM cattle may have a "generalized membrane defect" is still considered valid.
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