Sequential studies of skeletal calcium reserves and structural bone volumein a commercial layer flock

1. Production-induced osteoporosis in caged laying hens is thought to repre sent a major constraint to continued genetic development. 2. The relationship between body weight, egg production, skeletal abnormali ties characteristic of osteoporosis, femur calcium and bone histology was e xamined in a flock of ISA Brown layers from 16 to 68 weeks of age. 3. Experiment 2 examined a flock of Lohmann browns for skeletal abnormaliti es characteristic of osteoporosis at 45 weeks of age and the severity of ab normalities was then related to body weight and production between 18 and 4 5 weeks of age. 4. Average body weight declined in the ISA flock between 35 and 45 weeks of age, which correlated with a loss of skeletal calcium reserves (15% to 20% ) and with the induction of osteoporosis. Between 42 and 68 weeks of age, b irds were able to replenish femur calcium levels. 5. Birds in the Lohmann flock showing severe skeletal abnormalities at 45 w eeks of age experienced weight loss between 27 and 31 weeks of age, which w as associated with a decrease in egg production of 18%. After 35 weeks of a ge, egg production of these birds recovered to similar levels as unaffected or mildly affected birds. 6. It seems likely that better standardisation of the equilibrium between g rowth, skeletal reserves, food intake and egg production can reduce osteopo rosis, as well as improving the productive potential of modern laying strai ns.