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Effect of Level of Dietary Zinc and Source and Level of Corn on Performance and Incidence of Parakeratosis in Weanling Pigs

Cornell University^,2, Ithaca, New York

Abstract

One hundred sixteen Berkshire, Yorkshire and Berkshire x Yorkshire weanling pigs were used in five experiments to study variations in performance and parakeratosis associated with high-calcium rations differing in zinc level and in source and level of corn. Precautions were taken to minimize zinc contamination of the environment.

A 17% protein corn-soybean meal-type basal ration containing 1.3% calcium and 30 to 34 ppm of zinc produced weight gain equal to that obtained with the same ration supplemented with zinc to supply a total of 61 to 77 ppm of zinc in all cases where New York corn was used. In one experiment using Illinois corn, pigs gained significantly less weight during the first four weeks when the ration was not supplemented with zinc, but this difference disappeared by the end of the trial. No parakeratosis (PK) occurred. When the calcium content of the ration was increased to 1.84% by additional limestone PK appeared in two of four pigs fed the low zinc Illinois corn ration but in none of those fed the low zinc New York corn ration or in either the Illinois or New York ration with added zinc. In another experiment there was no difference between New York and Michigan corn or in zinc level in affecting weight gain and no PK was produced.

When 40% glucose replaced corn by weight in the basal ration containing New York corn, to decrease the zinc content from 34 ppm to 21 ppm, it caused PK in six of 16 pigs after 30 days. Weight gain was slow and PK aggravated when half of the pigs were continued on this ration for an additional 15 days, but weight gains were stimulated and lesions disappeared in pigs transferred to the basal corn ration containing 34 ppm zinc. When the treatments were reversed, the basal corn ration again brought about an improvement in weight gain and disappearance of PK. In another experiment PK developed in pigs fed the 40% glucose ration (21 ppm of zinc) and in those fed the same ration supplemented with zinc to supply a total of 33 ppm of zinc but not in those fed the basal corn ration (34 ppm of zinc).

Under the conditions of these studies the amount of zinc required to prevent PK and promote maximum weight gain in pigs fed a basal corn ration containing 1.3% calcium appears to be no greater than 34 ppm. Evidence is presented indicating that there may be differences among samples of corn in the availability of the zinc they contain and that some samples may contain a protective factor against PK. Possible factors include variation in the phytic acid content, presence of a naturally occurring agent that enhances zinc utilization and trace minerals other than zinc.

¹ The authors gratefully acknowledge F. E. Lovelace for calcium analyses, Miss S. Spitz for proximate analyses, V. Lazar for zinc analyses, and American Cyanamid Co., Princeton, New Jersey; Nopco Chemical Co., Newark, New Jersey; Merck and Co., Rahway, New Jersey; and Dawe's Labs., Chicago, Illinois, for supplying some of the feed ingredients.

² Department of Animal Husbandry.