The role of body composition in the onset of lay of Japanese quail (Coturnix coturnix japonica)

This study was designed to examine the influence of dietary protein and restricted feeding on body composition of Japanese quail at the onset of lay. The first experiment utilized five isocaloric diets containing either 26%, 24%, 20%, 16%, or 14% crude protein. Each diet was fed to three groups of quail: one group was fed ad libitum, a second group was fed 80% of ad libitum, and the third was fed 60% of ad libitum intake. Age at the onset of lay was successfully delayed. The quail fed the lower protein levels entered lay at later ages than those fed the high protein diets. Likewise, the restricted fed groups achieved lay at later ages than the ad libitum fed groups. Other traits examined in this experiment including body weight, breast weight, abdominal fat pad weight, carcass lipid and shank length produced inconsistent results.

The final experiment incorporated identical diets and feeding regimes as the previous study. Age at the onset of lay was influenced by dietary protein level and feeding regime. The dietary protein level by feeding regime interaction was also significant. The groups fed the higher protein diet ad libitum tended to enter lay at younger ages than did the groups fed restricted amounts of the diets containing less protein. The other traits measured were more consistent than in the first experiment. The early maturing quail tended to enter lay with heavier body weights1 larger breast percentage and lower carcass lipid percentages. The last groups to achieve lay did so with lower breast weight percentages and higher carcass lipid percentages. Shank length, or skeletal growth, also may have been an important factor in the onset of lay. This effect was apparently independent of lean tissue. Adipocyte cellularity measurements were inconsistent.

Body composition differences were apparent as age at the onset of lay was increased by dietary manipulations. It was speculated that early maturing quail reach oviposition when a minimum chronological age or "critical" lipid level was reached. The late maturing quail entered lay when a "critical" lean percent or skeletal size was attained. The intermediate maturing quail, like the late maturers, achieved oviposition when percent lean or skeletal size reached "critical" levels. Thus, one of these four factors appeared limiting for each group to achieve lay. The attainment of the critical level of the limiting trait allowed the quail to achieve sexual maturity.