GENETIC AND NONGENETIC EFFECTS ON ERYTHROCYTE OSMOTIC FRAGILITY IN LACTATING HOLSTEIN COWS AND ITS ASSOCIATION WITH YIELD TRAITS

Blood samples from 262 lactating Holstein cows were analyzed to determ ine the resistance of erythrocytes to hypotonic NaCl solutions. The an imal model contained stage of lactation, herd, parity, and season as f ixed effects, milk yield as a covariate, and 520 random animal effects . A derivate-free algorithm of REML procedure was applied for estimati on and prediction. The results suggested higher hemolysis rates and me an corpuscular fragility in first than in later lactations and decreas ed erythrocyte fragility in cows in late lactation. A negative linear regression of percentage of hemolysis on weekly milk yield was signifi cant. Heritability estimates were .58 +/- .14 for hemolysis rate at 11 1 mM NaCl and .47 +/- .18 for mean corpuscular fragility. Estimates fo r hemolysis rates decreased with increasing osmotic fragility at lower NaCl concentrations. Phenotypic correlations between erythrocyte frag ility traits and 305-d milk, fat, and protein yields were all negative and low. Moderately negative genetic correlations between red blood c ell osmotic fragility and fat yield and fat percentage and slightly po sitive genetic correlations between red blood cell osmotic fragility a nd protein yield and protein percentage suggested possible alterations in erythrocyte membrane stability if milk component traits were targe ts for genetic selection.