Diurnal Change in the Rates of N^τ-methylhistidine Excretion in Laying Hens

Abstract

N^τ-methylhistidine (N^τ-MH) excretions were measured in laying and nonlaying hens to show the role of the skeletal muscle as a source of amino acids for egg protein synthesis. Four 10-month old laying hens and 3 117-day old non-laying hens were housed in individual cages and fed the experimental diet containing 15% protein. The diet was made mainly of corn and purified soybean protein. After 7 days of pre-feeding of the experimental diet, whole excreta samples were collected to measure N^τ-MH every 4 hours in the daytime starting at 7a.m. The excreta samples were also collected in the evenings (7p.m.-7a.m.) of the seventh and eighth days. In the laying hen, the peak of N^τ-MH excretion was observed between 4-8 hours after oviposition, and the rate of N^τ-MH excretion at the peak was about 2 times the rate before oviposition. However, in the non-laying hen, there was no diurnal variation of the rate of N^τ-MH excretion, and the rates were much lower than those of the laying hen. The results clearly show that there is a diurnal variation of the skeletal muscle protein breakdown in the laying hen and that skeletal muscle protein breakdown is accelerated when egg protein is intensively synthesized.