The use of early partial egg records as a selection criterion for improving annual egg production was proposed by Dempster and Lerner (1947). Their proposal was based on the contention of Dickerson and Hazel (1944) that genetic gain should be evaluated per unit of time, and that, under certain conditions, the genetic gain per unit of time could be increased by reducing the age of the parents.

Much of ectoparasitic arthropods to the poultry industry, and also of the means for their control (e.g. Furman, 1963; Simco and Lancaster, 1965; Anon. 1969). The same cannot be said, however, of all the non-parasitic arthropods which live in association with poultry, about which almost nothing has been published.

In building up highly productive egg laying strains of hens and in subsequent work with them correct evaluation and purposeful selection of sires is of high importance.

Until recently evaluation and selection of cockerels for conformation and their mothers’ productivity were the principal methods used although the coefficients of correlation between the productivity of cockerels’ mothers and that of their daughters are not high. This is because their mothers’ phenotypic performance depends not only on the genetic contribution but also on the effects of environment. The latter plays a considerable role in either checking or realising the genetic potential.

The cystic structure commonly called "breast blister" occurs on the ventral aspect of the sternal crest of the keel bone of chicken and turkeys. The cyst is usually filled with a viscious, clear fluid which may appear dark in color in advanced cases. Blisters vary in size and prominence from those detectable only by careful palpation of the area to those involving the entire sternal crest.