1. Growth and feed conversion efficiency of pigs between weaning and 100 lb. live weight were improved by adding a vitamin B12 a supplement to simplified all-plant rations containing, principally, barley and groundnut meal. This response was obtained with less than one-third of the U.S. recommended allowance of vitamin B12 in the rations of growing pigs.
2. No such response was obtained when a vitamin B12 supplement was added to rations containing milling by-products and grass meal.
3. When pigs were fed to a scale based on live weight, those that received an all-plant ration (containing milling by-products and grass meal, and relying on groundnut meal as the main source of supplementary protein to give a total content of 18·4 to 18·8% crude protein) gave 90–93% as good growth as pigs that were fed rations of similar total digestible nutrient content containing 14·5–15·5% crude protein and 3·6 or 7·0% white fish meal. Calculations suggest that such groundnut meal rations may be slightly deficient in lysine, but probably not deficient in tryptophan or ‘cystine + methionine’.
4. When pigs were fed to appetite, those that received rations containing 3·6% white fish meal and no milling by-products or grass meal, ate significantly more than those that had either ‘milling by-products + grass meal’ or no fish meal in their rations; they grew proportionately faster, with no improvement in the efficiency of feed conversion.
5. The carcasses of pigs that had received all-plant rations from weaning to bacon weight were of good quality, and their measurements did not differ from those of pigs that had received fish meal to 100 lb. live weight.