Characterization of Na+, K+ ATPase in erythrocytes of dairy cows: effect of diet and genetic selection for milk solids

The number and activity of Na + , K + ATPase units were assessed with 3 H-ouabain binding and 86 Rb + uptake methods, respectively, in erythrocytes from second-parity Holstein–Friesian cows at weeks 10 and 24 of lactation. The cows were either from S or C genetic lines for yield of milk fat and protein and were offered diets of either H or L forage content. The Scatchard method of analysis indicated that 3 H-ouabain binding was compatible with a single class of receptors of high affinity. S-line cows had higher milk yields (P