The literature concerning the influence of ahemeral light cycles on the quality of eggs is reviewed. Results pooled from published reports were used to arrive at a quantitative relationship between the length of light cycle (ranging from 23 h to 30 h) and the parameters of egg quality. Eggshell quality (whether measured as mg shell per unit surface area, as shell thickness or as shell weight per se) was found to depend on a curvilinear function of cycle length. Albumen height was negatively correlated with cycle length, whereas yolk and albumen weights were found to have a curvilinear relationship with cycle length.

Egg yolk is an obvious source of fat in our daily diet. The trend towards a reduction in fat consumption and concern over the quality of any fat that is consumed have caused a significant erosion of the previously accepted dietary image of the egg. In spite of the extensive and continuing controversy over the quality of dietary fat and the incidence of coronary heart disease, it is now widely recommended that the consumption of animal fats does not predispose to health. Parameters describing what is a healthy dietary fat have been established. Egg fat is examined with regard to these parameters and the justification for its present poor image is scrutinized. So firmly entrenched are the present views on animal fat consumption, that to rehabilitate the egg with the consumer will require a change of approach, away from the complacency of the past to a more positive approach based on attempts to change lipid parameters to align with present consumer perceptions and requirements.

Salmonella enteritidis phage type 4 was recovered from the yolk sacs of broiler chickens in East Anglia, UK, during 1987. When the same phage type 4 was identified in two of the supply flocks, transovarian infection was suspected. These findings were of particular interest to the Public Health Laboratory Service because they provided a possible explanation for the unprecedented increase in food poisoning during 1988 linked to the consumption of shell eggs. Some of the problems of diagnosis are discussed in breeder hens and in the progeny. Effective control of S. enteritidis phage 4 in poultry is dependent on the accurate detection of infected breeder/layer hens in which vertical transmission is the essential distinguishing feature from most other non-invasive, enteric salmonellas found in poultry. The mandatory testing of poultry flocks by the UK Ministry of Agriculture introduced in March 1989 has led to the compulsory slaughter of a large number of birds as prescribed by the Zoonosis (1989) Order. The benefits of this policy should soon become apparent to poultry producers and to the consumer.

The control of important poultry diseases in Asia is described, with the emphasis on vaccines, vaccination programmes and procedures. In most Asian countries there is routine vaccination for Newcastle disease, Marek's disease, infectious bronchitis, infectious avian encephalomyelitis, fowl pox and fowl cholera. However, depending on local conditions, programmes and procedures may differ from one country to another, or even from one farm to another within the same country. While some of the vaccines used are manufactured within the countries of the region, a large number are imported. India is the only Asian country that is self-sufficient in vaccine production.

When multiple linear regression of feed consumption on metabolic body weight (MBW), body weight gain (BWG) and egg mass production (EM) is calculated between or within strains of laying hens, a standard deviation of 47–180 kJ metabolizable energy (ME) per day remains unexplained by these effects. This unexplained fraction, called residual feed consumption (RFC), has a heritability of 0-80%. A survey of the literature was performed to quantify this unexplained variation between strains and among individuals within strains of laying hens with respect to some energy metabolism parameters independent of MBW, BWG and EM. Genetic differences in ability to metabolize gross feed energy are found to be of limited magnitude; the coefficient of variation is 1–3%. From calorimetric experiments, the range of heat production (HP) between strains is found to be 44–118 kJ kg−0.75 d−1; variation among individuals within strains is of the same magnitude (standard deviation: 16–125 kJ kg−0.75 d−1). The range of maintenance requirements (MEm) is reported to be 41–113 kJ kg−0.75 d−1; standard deviation among individuals is 23–80 kJ kg−0.75 d−1. Variation of heat increment of production (constituting the difference between HP and MEm) seems to be small. The main component of HP variation and of RFC variation seems to be the variation of MEm: differences in physical activity, feathering density, basal metabolic rate, area of nude skin (comb, wattles, legs), body temperature and body composition. Net energy per g EM does not play an important role in variation of RFC.

A chronological account of observations on the nature of the shell membrane protein system is presented. The review indicates that although the major protein in the shell membrane is not elastin, it does contain desmosine and isodesmosine – the cross-linking amino acids. The membranes also contain small amounts of collagen. The formation of these proteins can be impaired by the inclusion of lathyrogens in the diet of laying hens. This impairment is caused by a failure to synthesize cross-links of membrane protein and this is very similar to the effect obtained when hens are fed copper-deficient diets. The disruption of the protein system has a considerable effect on the development of eggs, which are abnormal in size, shape and shell texture. The lathyrogens also have a depressing effect on egg production. The problems and prospects of utilizing seeds of certain Lathyrus plants containing lathyrogens are indicated.