Egg characteristics and production efficiency of dwarf (dw) White Leghorn hens divergently selected for body weight.

Egg characteristics, feed efficiency (egg mass/daily feed intake), and performance efficiency (egg mass/body weight) were studied in dwarf White Leghorns after four generations of selection for divergent body weight at 20 weeks of age. Sexual maturity and livability were not significantly different among high (H), low (L), or control (C) lines. Mean 20-week body weights for H, L, and C lines were 1.50 kg, .76 kg, and 1.02 kg, respectively. Daily feed intake, egg mass, egg weight, and yolk, albumen, and shell weights were significantly (P less than .05) different between H and L hens and were directly related to body weight. Percent yolk was greatest and percent yolk mottling and percent albumen were lowest in eggs from L hens. Percent shell was not significantly different among the lines. Albumen quality (Haugh units) was significantly better in eggs from H and L hens than from C hens. Percent hen-day egg production was not significantly different among lines. Feed efficiency was greatest in C hens with both C and L hens significantly more efficient than H hens. Performance efficiencies of C and L hens were significantly better than H hens throughout the experiment, and L hens were significantly more efficient than C hens during peak egg production. These results suggest that there may be minimum body weight requirements for efficient egg production.