Studies on Zinc

Abstract

Young rats weighing between 40 and 50 gm. were placed in groups of 5, three females and 2 males, in screen bottom cages. Food and water were supplied ad libitum. C. P. zinc carbonate was incorporated in the growing ration at 3 levels, corresponding to 0.10, 0.50, and 1.00% of zinc. The growing ration is a mixture of naturally occurring foods, and has served this laboratory well, during many years, for the growth and reproduction of rats. The zinc salt contained as a maximum the following impurities: arsenic 0.000%, chloride 0.002%, iron 0.01%, lead 0.002%, nitrate 0.000%, and sulphate 0.01%. Hemoglobin was determined by the Newcomer method.

Growth was normal on the rations containing 0.10 and 0.50% of zinc. The animals were vigorous when the experiment terminated, and there was practically no difference in the weight of the rats receiving zinc and those on the stock diet. The limit of tolerance to zinc carbonate lies between 0.50 and 1.0% of zinc in the diet. The animals on the 1 % zinc diet failed to grow in the majority of cases, although some individuals weighed 140 to 160 gm. after 10 to 12 weeks. Some of the animals began dying within 4 weeks after being placed on this diet; some were partly eaten.

Growth and reproduction on the lowest level of zinc were normal. Several generations of these rats on the same zinc diet have shown no abnormalities. Reproduction was markedly affected, when the animals received 0.50% of zinc. The females on this diet became pregnant between the fourteenth and seventeenth weeks. One female had 3 young and lost 30 gm. at parturition. Another female had 3 young (one born dead) but lost 40 gm. at parturition.