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Abstract
1. Egg production records of 31 455 individually caged hens, 27 to 34 weeks of age and of 4 genotypes, were examined.
2. Sixty‐nine non‐layers were identified in the 30 to 40 week age group, and examined post mortem; an incidence of 2.1 per 1000.
3. Some of the 69 individuals had more than one abnormality. Forty‐two percent were internal layers, 34% had some form of neoplasia, 24% had an abnormal or diseased oviduct, 18% were sex reversals, 16% had a diseased ovary, 8% were of poor condition and considered culls, and 7% were in good condition, but with small, immature ovaries.
4. Of 54 birds not in lay at 27 weeks, 43 (80%) had come into lay by 34 weeks of age.
5. Genotype influenced the incidence of neoplasia and, in turn, the number of non‐layers.
