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The effects of changes in zinc intake on weight gain, plasma Zn concentration and the development of clinical lesions of Zn deficiency have been studies in Zn depletion and repletion studies with calves and lambs. 2. A basal diet, the principal components of which are urea, dried egg white, starch, glucose, cellulose and arachis oil has been developed for trace element deficiency studies with ruminants. 3. Weight gain ceased abruptly in both calves and lambs when either the unsupplemented basal diet was given or when Zn supplements provided only 0.05 mg Zn/kg live weight per day. Mean plasma Zn concentrations in these animals fell from pre-experiment values of between 0.8 and 1.2 μg Zn/ml to below 0.4 μg Zn/ml after 1 week on these treatments. 4. Supplements providing 0.2 mg Zn/kg live weight per day were sufficient to maintain a good rate of growth but insufficient to prevent a fall in plasma Zn. 5. Growth arrest occurring within 2 weeks and a rapid fall in plasma Zn occurring within 1 week after Zn supplements were withheld from calves and lambs that had previously received 0.7 mg Zn/kg live weight per day for 6 and 14 weeks respectively indicated that these species have only a limited capacity to store Zn in a form that can be utilized during periods of inadequate Zn intake. 6. Tentative estimates are presented of the Zn requirements of calves maintained on this type of basal diet and the influence of ration composition of Zn availability is discussed. 7. The possible value and the limitations of plasma Zn determination as an aid to the field diagnosis of Zn deficiency are considered.
Mills et al. (Fri,) studied this question.