N tau-methyl histidine excretion by poultry: not all species excrete N tau-methyl histidine quantitatively.

The rate of elimination of administered N tau-[14CH3]methyl histidine was used to assess the validity of N tau-methyl histidine excretion as an index of muscle protein breakdown in poultry. Broiler chicks (2-3 and 4-5 weeks old), laying hens, adult quail (Coturnix coturnix japonica), adult cockerels and turkey poults (2-4 weeks old) were tested. All except the turkey poults showed quantitative recoveries of N tau-[14CH3]methyl histidine within 1 week. Turkeys showed a different pattern of N tau-[14CH3]methyl histidine output; the mean total recovery after 14 d was less than 50% of the injected dose. The majority of the label remaining after this time was found in breast muscle. All birds tested excreted N tau-methyl histidine unchanged, although a small amount sometimes appeared as another metabolite. No significant oxidation of N tau-[14CH3]methyl histidine by broiler chicks turkey poults or adult quail was found. The results show that excretion of N tau-methyl histidine is a useful measure of muscle protein breakdown in the domestic fowl and quail but not in turkeys.