Zinc-65 absorption and tissue distribution in two- and six-month-old holstein calves and lactating cows.

Holstein calves and cows in first lactation were fed a low-zinc (16.6 ppm) experimental diet. Zinc-65 absorption and tissue distribution were determined following a single oral tracer dose of zinc-65 given 14 days prior to sacrifice. Net zinc-65 absorptions for the cows and 2- and 6-mo-old calves were 53.4, 49.7 and 47.2% of the dose. Tissue zinc-65 content, adjusted for body weight and zinc-65 of milk of the cows was not significantly different from that of either age calves in 13 of 20 comparable tissues. Greatest differences in tissue zinc-65 were in tibia and rib with the 6-mo-old group highest and cows lowest. Lactation represents a major homoeostatic demand for zinc, and the intestinal absorptive ability of adult cattle remains responsive to physiological need.