Differences in some blood characters between Zebu type cattle, British breeds of cattle, and crosses between these two types are delineated. Zebu type animals tend to have higher packed cell volumes, erythrocyte sodium concentrations, whole blood specific gravities, and gene frequencies for the fast-moving haemoglobin, and lower erythrocyte potassium concentrations and median corpuscular fragilities, than British breeds. The results are discussed in relation to endocrine balance and methods which have been developed for the assessment of adaptation of cattle to tropical and subtropical environments. The concentration of potassium in erythrocytes is suggested as another possible index of adaptation potential in cattle.
The following red cell characters were studied in a herd of 217 calves repre-senting Brahman cross, Africander cross, Grade Brahman, and British (Hereford X Shorthorn) breeding, and in their dams: packed cell volume, haemoglobin level, red cell count, fragility, potassium and sodium concentrations, catalase activity, and haemoglobin type. There were distinct breed differences. In some characters, e.g. packed cell volume and potassium concentration, Africander cross were inter-mediate between Brahman cross and British, whereas in others, e.g. fragility and catalase activity, they were indistinguishable from British. Within breeds, the characters showed highly repeatable differences between animals and high herita-bilities.
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