[Studies on the methionine-threonine imbalance in chicks]

Experimental lots of 12 chicks each received, in addition to their standard diets, supplements of 1, 2 or 3% DL-threonine, in each threonine treatment 1, 2 or 3% methionine being added. After an 8-day feeding period the chicks were injected 35S-methionine and were killed after 6, 12 and 24 hours, respectively. The increasing methionine supplementation was found to markedly deteriorate chick growth. It was not possible to correct this effect by any of the threonine doses. The 35S-activity of the blood decreased very strongly from the 6th to the 12th hours following injection. The 35S-activity of the liver also declined clearly at low threonine supply, but less markedly at high threonine rates. In the breast muscle, the 35S-activity also proved three times higher 24 hours after the injection at equal methionine supplementation to the diet (1 or 2%) and at triplicated threonine level (3% against 1%). This finding is related with the fact that threonine supplements to not attenuate the negative imbalance symptoms after methionine overdosing, but that they are likely to aggrevate due to transport competition. The possibility of threonine degradation into glycine does not seem to be of importance for methionine detoxication in chicks.