The Riboflavin Requirement of the Growing Pig at Two Environmental Temperatures

Abstract

In two experiments involving 8 young pigs each, the riboflavin requirement was determined at environmental temperatures of 85°F. and 42°F., respectively. In each experiment the pigs were depleted of the vitamin by subsistence for three weeks on a semi-synthetic ration containing 0.2 to 0.4 p.p.m. of riboflavin. During subsequent experimental periods of 7 or 8 weeks at the respective temperatures, the pigs were fed 8 different levels of the vitamin, ranging from the basal level to 4 or 5 p.p.m. The food consumption was equalized among all pigs in each experiment except when the pigs on the lower levels developed symptoms of deficiency. The adequacy of the riboflavin concentration was determined by the appearance and behavior of the pigs, the rate of growth and the blood picture. The most significant morphological change in the blood associated with incipient riboflavin deficiency in the young pig is a marked increase in the concentration of neutrophilic granulocytes and in the percentage of these cells in the total leukocyte count. The results clearly show that the riboflavin requirement is higher at the lower temperature, the requirements being approximately 1.2 (or somewhat less) p.p.m. at 85°F. and approximately 2.3 p.p.m. at 42°F. These values are equivalent to 0.55 and 1.59 mg of riboflavin per pound of feed and 1.4 and 4.2 mg per 100 lb. body weight, respectively. Confirmation of this effect of temperature on the riboflavin requirement is found in the results of preliminary experiments on older pigs, revealing a consistently smaller spillover of riboflavin in the urine, on the smae diet, at 42°F. than at 85°F. Auxiliary data on pigs show that supplements of protein and of fat added to a diet of natural feeds depress the output of riboflavin in the urine, indicating, though not proving, an increased requirement of the vitamin under conditions of increased assimilation of protein and fat. Similar tests with glucose supplements yielded negative results. The riboflavin requirement of animals per unit of air-dry food seems to be independent of body size. Hence, this method of expressing the requirement is preferable to expression per unit of body weight.