Several interrelationships are apparent between egg weight, chick weight, chick growth and other parameters. The hatchability of intermediate size eggs is better than that of very large or very small eggs. Decreased hatchability, hatchling weight, chick growth and chick viability have been associated with the first few eggs produced by young pullets. Incubation time is positively correlated with egg size. Embryo weight is not correlated with egg weight during the first half of the incubation period. Thereafter the correlation increases and reaches a maximum at the time of hatching (0.5–0.95). Chick weight is primarily determined by initial egg weight, normally being 62–78% of egg weight, and is secondarily determined by weight loss during incubation, shell and residue weight, strain, incubation time and conditions, breeder age and chick sex. The correlation of egg weight to posthatching chick weight decreases with increasing age of the chick. A 1 g change in egg weight has been shown to result in a corresponding change of 2–13 g in broiler weight at 6 to 8 weeks of age. This effect is much greater in eggs from young breeders than in those from old breeders. The effects of egg weight on chick feed conversion have been variable with no clear conclusion. Improved growth and uniformity may be obtained by growing chicks separately according to hatchling size. Therefore, sorting eggs by weight prior to incubation might be advantageous in some production operations to improve broiler or pullet uniformity and efficiency.

Feed efficiency data for growth selected and unselected and also stocks divergently selected for body weight were reviewed with special emphasis on changes immediately after hatching. Examination of feed efficiency differences between genetically diverse stocks from hatch to market age normally reveal only small differences in the efficiency of feed utilization. On the other hand, differences in feed intake appear to be the dominant factor in growth-related changes of these genetically diverse stocks. However, when data were segmented into periods which allowed investigation of differences at early ages, especially immediately after hatching, major differences in feed efficiency between genetically diverse groups were observed.

These data indicate that feed efficiency plays a more important role in explaining genetic differences in growth than indicated by previous investigations. The appearance of the greatest differences between genetically diverse stocks immediately after hatching indicates that early feed efficiency changes may allow for greater subsequent feed intake. Therefore, it appears that changes in early feed efficiency along with changes in feed intake both play major roles in explaining genetic differences in growth. The role of feed efficiency is apparently obscured by the maintenance requirements associated with large body sizes of selected stocks when measurements are obtained at older ages.

There are many different characteristics of housing systems which affect the welfare of laying hens, particularly because welfare itself has many diverse aspects. When cause and effect relationships between systems and welfare are assessed, it is evident that no system currently under consideration is ideal. Of those priorities listed by UK authorities such as the Ministry for Agriculture, Fisheries and Food and the Farm Animal Welfare Council, all systems are likely to provide ‘freedom from hunger and thirst, adequate lighting and the company of conspecifics’. However, conventional cages are less likely than other systems to provide ‘freedom of movement, freedom from fear, comfort and shelter, suitable flooring and freedom to display most normal patterns of behaviour’. Alternative systems, though, often expose birds to the danger of disease, to aggression from dominant birds and to the risk of cannibalism or beak trimming to avoid it. Overall, welfare is compromised more in conventional cages than in well-run alternative systems, though welfare is more sensitive to poor management and to market forces in the latter. Problems in cages are also less likely to be alleviated by genetic selection than those in alternative systems. The ideal system for present-day stocks should combine the small group sizes found in cages with the freedom of movement and complex environment characteristic of alternative systems.

Research efforts made to evaluate the production potential of the indigenous helmeted guinea fowl in Nigeria are highlighted, together with the possibility that guinea fowl could supply the population with more meat and eggs. The encouragement of large-scale production is justified because both the meat and eggs of guinea fowl are acceptable to the majority of Nigerians. The growth rate of unimproved local birds remains very low with 12-week body weights of around 530 g. The comparable 12-week weights for improved local and exotic stocks are about 770 and 1200 g respectively. The carcase yield and meat quality of guinea fowl surpass those of the domestic fowl. Egg production is seasonal and low in the wild (12–20 per bird), but domesticated stocks start to lay at 28–32 weeks of age and yield 60–90 eggs per reproductive female per season.

Live attenuated strains of Salmonella spp. make excellent vaccines against salmonellosis in experimental animals, eliciting a cell-mediated, mucosal and humoral immune response. In addition, new recombinant DNA technology permits the expression in Salmonella strains of protective antigens from unrelated bacterial, viral or parasitic pathogens. Exciting possibilities exist for a single live vaccine which could provide protection against two or more infectious agents. Recently, attenuated strains of the chicken pathogen Salmonella gallinarum have been considered as the basis of a live multivalent poultry vaccine and work is progressing on the expression of coccidial and herpes viral antigens in strains of Salmonella.

Throughout Asia and the Pacific region, inadequate supply of maize will limit further expansion of the poultry industries during the coming decade. In this context, the use of locally available energy feedstuffs merits increased attention. This review examines the potential feeding value and nutritional limitations of some carbohydrate sources, with special reference to Asia and the Pacific region. Some guidelines that may lead to better utilization of these feed resources are also discussed.

The non-starch polysaccharides (NSPs) of cereals exhibit anti-nutritive activity when present in broiler diets. The high levels of arabinoxylans (pentosans) in rye and β-glucans in barley are responsible for the poor nutritive value of these cereals. Australian wheats vary considerably in their nutritive value with some having very low apparent metabolizable energy (AME <13 MJ/kg) values. Recent studies have shown that the low AME wheat problem is probably due to the variation in the levels of the water-soluble wheat NSPs which are predominantly pentosans. When pentosans isolated from rye or wheat are added to broiler diets, dose-dependent depressions in nutrient digestion and growth occur. Several treatments have been shown to be effective in improving the nutritive value of cereals. Soaking the cereals in water or adding NSP-degrading enzymes decreases the anti-nutritive activity of the NSP. Addition of antibiotics to diets also has been shown to increase the nutritive value of diets with high levels of NSP suggesting that the action of these materials is, at least in part, mediated by the gut microflora.

The use of lysozyme as a food preservative and the factors affecting lysozyme activity (temperature, chemicals, processing and complexes) is reviewed. Lysozyme inhibits the growth of deleterious organisms thus prolonging shelf life. Chemicals used to improve the preservative effect of lysozyme and those that inhibit the enzyme are discussed along with the stability of lysozyme in various chemical environments. Lysozyme has been used to preserve fresh fruits and vegetables, tofu bean curd, seafoods, meats and sausages, potato salad, cooked burdock with soy sauce, and varieties of semi-hard cheeses such as Edam, Gouda and some Italian cheeses. Lysozyme added to infant feeding formulae makes them more closely resemble human milk.

Among poultry scientists there is an increasing interest in model building because models are useful in the investigation of the economic consequences of management decisions and in identifying gaps in current knowledge of the biological processes involved in production. In addition to empirical formulae giving the relationship between one or two dependent and one or more independent variables, more mechanistic models are needed to solve problems which involve more detailed ‘what if’ questions, in particular, those that take into account interactions between several factors influencing growth and require a fundamental knowledge of growth processes. The advantage of these models is that they can be used in a broader range of circumstances than empirical models. The development of such mechanistic models serves to identify several remaining gaps in our fundamental knowledge of the causal mechanisms of growth. The mechanistic models described in this review can be seen as a collection of several empirical models, each representing a part of the total biological growth process.

It can be concluded that in future a more quantitative exploration of the causal mechanisms in growth and their interactions with the environment will be needed for the development of a mechanistic, stochastic and dynamic model of growth in a broiler population.