Physiological profile of caged layers during one production year, molt, and postmolt: egg production, egg shell quality, liver, femur, and blood parameters.
A longitudinal study of a flock of Single Comb White Leghorn pullets was initiated at 19 weeks of age (preproduction) and continued through a production year, a forced molt, and for 4 months of postmolt production. A representative sample of hens was obtained at 12-week intervals during the first year and at subsequent selected times. Liver lipid, femur weight, femur volume, femur density, egg weight, shell weight, percent shell, milligrams shell/square centimeter of shell surface area, serum calcium, serum phosphorus, and serum alkaline phosphatase were determined. Percent hen-day production peaked at 90% and then declined by .6 to .7% each week during the first production year. After molting, percent hen-day egg production peaked at 80% and declined .9% per week over the subsequent 20 weeks. Egg weight increased continually during the first production year. Shell weight was greatest immediately postmolt; thereafter it declined. Shell thickness was greatest at 31 weeks of age and declined throughout the first year. After molting, the shell thickness of 83-week-old hens was similar to values of hens about 37 weeks of age. Serum calcium and phosphorus of laying hens were influenced by age, feed intake and environmental temperature. The lowest values occurred during hot weather. Liver lipid was lowest in nonlaying hens (17 to 20%) and was approximately 42% of dry weight in laying hens. Femur density was greater in laying than nonlaying hens.