The requirements of bacon and heavy pigs for lysine and methionine have been investigated. The trials employed 3rd and 4th cross Large-White × Essex pigs.

In the first trial, which involved 560 pigs during the 40 to 120 lb. growth stage, the amount of herring meal in the standard weaner diet was progressively reduced from 7 to 1%. Total protein was kept constant by including soyabean and groundnut meal.

Growth efficiency worsened progressively as herring meal was reduced but growth was restored by adding lysine and methionine to the levels of the 7% herring diet. The optimum levels of lysine for pigs during the 40 to 120 lb. growth stage appeared to be higher than reported elsewhere (0·85% against 0·76% and 0·65%).

Treatments prior to 120 lb. had no residual effects on growth during the 120 to 200 lb. stage when all pigs were on a normal fattening diet containing no animal protein and there were also no residual effects on the carcass composition of the pigs at 200 lb. live-weight.

The results support the view that the nutritional value of animal proteins to pigs lies solely in the quantity of essential amino acids that they supply. Under the conditions of this trial, the particular essential amino acids were lysine and methionine.

The second trial involved 260 individually and group-fed heavy pigs. Lysine supplementation of the barley-mineral diet during the 140 to 260 lb. growth stage improved food conversion and increased the lean content of the carcasses of heavy pigs fed ad lib.; with restricted feeding growth rate was also improved.

Under the conditions employed the optimum lysine content of heavy pig diet during the final growth stage is at least 0·67%.