The toxicity of sulphite. II. Short- and long-term feeding studies in pigs

Sodium metabisulphite (Na2S2O5) was added to the diet of groups of 20 male and 20 female pigs at levels of 0·0, 0·125, 0·25, 0·5, 1·0 or 2·0%. After 15 wk, 14 males and 14 females from each group were killed. The six males and six females remaining in each group were kept on the same diets for up to 48 wk. All diets contained additional thiamine (50 mg/kg diet). Special attention was paid to the loss of sulphite from the diets and to the thiamine status of the animals. The concentrations of sulphite still present in the various experimental diets when they were consumed by the pigs were calculated to be on average 0·06, 0·16, 0·35, 0·83 and 1·72% respectively. The thiamine levels in the urine and liver were markedly decreased in animals fed 0·16% sulphite or more, but the extra thiamine added to the diet prevented thiamine deficiency with sulphite levels up to 0·83%. There were no adverse effects on health, mortality or the blood picture, neither was there any evidence of occult blood in the faeces. The general condition of the pigs in the 1·72% sulphite group was less favourable than that of the animals in the other groups. At this dose level the gain in body weight and food conversion were unfavourably affected. Growth was slightly decreased also at the 0·83% level. The effects of sulphite on growth and food conversion were due to less palatable diets, as indicated by a paired-feeding study. Organ-to-body weight ratios of the liver, kidneys, heart and spleen were increased with dietary levels of 0·83 and 1·72%. The increase in heart and spleen weights could be ascribed to the lower body weights of these groups. Damage to the stomach was apparent from the mild inflammatory and hyperplastic changes noticed in the gastric mucosa of several animals fed 0·83 or 1·72% sulphite. A pigmentation of the caecal mucosa resembling pseudomelanosis coli was observed at the two highest dose levels, but was considered to be of minor, if any, toxicological significance. The no-effect level established in this study was 0·35% Na2S2O5 in the diet of pigs for 48 wk. © 1972 Pergamon Press Limited.