A series of trials were designed to determine the slaughter weight of cutting pigs at which lean meat production is most economical, and to investigate nutritional factors which affect lean meat onput in cutting pigs of about 260 lb. live-weight. The trials involved about 1100 pigs and ad lib. feeding was adopted from weaning to slaughter.

In the first trial, pigs were fed on various diets to 300 lb. live-weight. The diets differed in the amount of protein fed during the 90–180 lb. growth period, and the most economic growth was made by feeding a high protein (17 %) diet to 140 lb., or a medium protein (14 %) diet to 180 lb. followed by a cereal-mineral diet thereafter to 300 lb.

Animals were slaughtered and dissected at various live-weights between 90 and 300 lb. and it was found that killing-our percentage, the percentages of usable meat (lean plus fat) and of fat, increased with carcass weight. The increase in fat deposition was mainly at the expense of the non-edible parts of the carcass. Onput of lean and increase in area of eye muscle occurred throughout the range.

Total food requirements, expressed as pounds of food, calories of gross energy or pounds of protein, per pound of usable meat produced decreased as slaughter weight increased. The cost of food required to produce a given quantity of lean meat was least when pigs were slaughtered between 240 and 260 lb. when the commercial value of the remainder of the carcass was taken into account.

The second trial investigated the effect of two levels of protein and mineral supplementation of cereals during the 140–260 lb. growth period of heavy pigs. Correct mineral supplementation of cereals was essential because, although lean meat production was not increased, the cost of food required to produce it was less. The lower protein diet had no effect on growth or carcass composition, but the higher protein diet increased the lean meat content of carcasses and decreased the amount of food required to produce it. The production of the extra lean meat, however, was not economical because of the cost of the high protein diet.

The third trial showed that replacement of barley by wheat during the 140–260 lb. growth period led to carcasses having less lean meat and to higher feed requirements. This is probably connected with the high energy content of wheat as compared to barley.