In chickens, metabolism is influenced by environmental factors and of particular interest nutritional factors, such as diet quantity and composition. With respect to the dietary macronutrients, literature clearly shows that in isoenergetically formulated diets, the protein level has a pronounced effect on metabolism, whereas fat and carbohydrate concentrations play a limited role. A decreased dietary protein level results in depressed growth rates, with reduced carcass gains in both water and protein content. In spite of the lower protein retention in chickens fed low protein diets, the efficiency of utilization of dietary protein appears to be increased. This indicates an inverse relationship between protein intake and utilization, which is reflected in decreased circulating uric acid levels. In addition, feed intake is increased, at least when protein levels are slightly reduced, leading to an involuntary overconsumption of energy compared to protein. The chickens deal with this excess energy consumption by increasing de novo lipogenesis and fat deposition, which is supported by increased plasma triglyceride concentrations, and heat production is increased. In contrast to adult mammals, the dietary macronutrients have no effect on diet-induced thermogenesis, nor is there any relationship between diet-induced thermogenesis and feed intake. Plasma growth hormone levels are higher in chickens reared on a low protein diet, indicating a causal relationship between growth hormone secretion and protein efficiency. In spite of the increased growth hormone levels, plasma insulin-like growth factor concentrations are lowered in low protein reared chickens, and may be partially responsible for the reduced growth rate observed in these animals. Plasma corticosterone concentrations are augmented in chickens on low protein diets, despite a decline in the ACTH concentration. Finally, plasma T3 and T4 levels are well known to increase and decrease, respectively, with decreasing protein content, whereas the effects of dietary macronutrients on circulating leptin levels require more research.

Embryonic development is a dynamic process that requires a fine balance between several factors in order to achieve an optimum hatchability and chick quality. These factors include the background of the embryo, such as genetic line of the breeders, the age of the breeder, egg weight, and factors related to the environment in which the egg is stored and incubated, such as temperature, humidity, gas levels and altitude. Gas exchanges are of fundamental importance for embryonic development during incubation and may affect the livability of the embryo. This paper reviews the roles of the gaseous environment (i.e. O2 and CO2) around hatching eggs during storage and during incubation and the effect it might have on the survival of the developing embryos and the chicks that hatch. The state of the art on the different attempts to establish the optimum requirements of different gases that promote the optimal developmental trajectories at different periods during incubation is presented. The roles and consequences of different levels of O2 and CO2 during storage and incubation on hatchability, incubation duration, hatching process, embryo growth, embryo mortality, organ development and morphology, metabolism, blood acid-base balance, chick quality and chick post-hatch growth are reviewed.

A well-designed environmental control system is the most efficient tool to ensure optimal production in livestock housing. In countries having a hot climate, such as Spain, the former comprises a large proportion of the capital invested in housing, and it deserves a thorough assessment. Most of the research carried out has been done in countries with a temperate climate and considering short hot periods, or even without them. The efficiency of the evaporative cooling system, which is commonly used in hot climate areas, depends upon the pad wetted surface area exposed to the passing air. Keeping the chosen inside temperature requires a definite cooled down of the outdoor air that is related to the ‘temperature tolerance’, i.e. the difference between inside and incoming air temperatures. The objective of this work was to establish the temperature tolerance when using the steady-state heat balance in commercial poultry housing. The heat balance estimates were imbalanced whenever the difference between indoor and outdoor temperature was less than 2°C. Substituting the exhaust air temperature for the indoor temperature in the expression that provides the heat drawn out through ventilation balanced the heat equation. The difference between inside and incoming air temperatures, temperature tolerance, has to be at least 2°C.

Wheat is a common ingredient in poultry diets, especially in Europe. Due to its low protein and high starch levels, wheat is essentially used as an energy supplier. Nutritional values of wheat samples vary according to their nutrient content and digestibilities. Variations of nutrient contents may be associated with cultivars and environmental conditions. Digestibility variations in growing chicks may be associated with these factors, and also, with technological treatments of diets and genetic origin of birds.

Total nutrient content (starch, protein, lipids and sugars) is strongly related to fibre content through a negative relationship. A large part of fibre content variations of wheat samples depends on their cultivar origin. Wheat protein content depends both on cultivar and environmental conditions. High yield cultivars are often associated with low protein content.

Lipid and starch digestibilities of wheat diets given to growing birds may sometimes be rather low.

The main reason of the low lipid digestibility values observed with some wheat samples is the high viscosity of water-extract induced by their water-soluble arabinoxylans. This viscosity results from a combination of several variables including the potential applied viscosity value (PAV as mL/g) of the wheat cultivar, the endogenous and exogenous xylanases, and the endogenous anti-xylanase contents. Environmental conditions and technological treatments are major factors acting on xylanase and anti-xylanase contents.

A part of wheat starch digestibility variations may be related to accessibility problems in coarse particles due to hard wheat cultivars and coarse grinding. However, coarse particles may be positive for stimulating feed intake of mash diets, and protecting against intestinal transit disorders.

In growing chicks, genetic origin of birds may result in very large variations in the digestibility of wheat diets, as observed with the divergent D+ and D− “Digestion” lines selected on the digestion ability of a wheat diet. In 3 w old chickens selected over 4 generations, the AMEn value of a Rialto wheat diet was 13% lower in D− than in D+birds (P=0.0001). D− birds showed 10% variations in AMEn values between four cereal diets (P=0.0003), while D+ birds showed only 4% variations (P=0.0006). In D+ birds, AMEn values of wheat and maize diets were the same (14,488 vs. 14,538 J/g DM), while, in D− birds, AMEn values of wheat diets were 5% lower (P=0.015) than the maize diet value (13,106 vs. 13,809 J/g DM).

Chicken is one of the most important sources of animal protein for human consumption, and breeding programmes have been responsible for constant improvements in production efficiency and product quality. Furthermore, chicken has largely contributed to fundamental discoveries in biology for the last 100 years. In this article we review recent developments in poultry genomics and their contribution to adding functional information to the already existing structural genomics, including the availability of the complete genome sequence, a comprehensive collection of mRNA sequences (ESTs), microarray platforms, and their use to complement QTL mapping strategies in the identification of genes that underlie complex traits. Efforts of the Brazilian Poultry Genomics Programme in this area resulted in generation of a resource population, which was used for identification of Quantitative Trait Loci (QTL) regions, generation of ESTs and candidate gene studies that contributed to furthering our understanding of the complex biological processes involved in growth and muscular development in chicken.

Shea nut (Vitellaria paradoxa, Gaertner or Butyrospermum parkii, Kotschy) meal, a solid residue from the shea fat industry, is available in large quantities in West Africa. The meal is now receiving increased attention as a potential feed ingredient for poultry due to the increased amounts that are available due to high demand for shea fat in cosmetics and as a cocoa butter substitute in chocolate. Studies have shown nutrient compositions (g/kg dry matter basis) of crude protein (80–250), ether extract (17–362), crude fibre (53–138), ash (33–76) and nitrogen-free extract (318–675); probably with the major part of the variability being due to the amount of fat extraction, handling of the nuts prior to processing, or seasonal effects on nut production. Anti-nutritive factors reported include saponins (3.0–30.0 g/kg), tannins (98.7–156.4 g/kg) and theobromine (4.5 g/kg), which may have detrimental effects on performance of poultry. However, it has been shown that fermentation (i.e. wet incubation of a feedstuff) has the potential to reduce the negative effects of some of these anti-nutritive factors. It is evident that shea nut meal has low nutritive value; therefore it requires further improvements before it can become useful for the poultry feed industry.

This review summarizes the environmentally friendly methods that are available to manage phosphorus (P) excretion. Phase feeding reduces P excretion up to 10–25% by adding precise amounts of P to broiler diets. Increasing of the Ca:P ratio in diets from 1: 1 to 2: 1 decreased the availability of P from phytic acid. Feeding diets supplemented with vitamin D can increase phytin P (PP) utilization from 31–50 to 68–87%. Total P (TP) excretion by poultry may be reduced by up to 50% through the use of supplemental phytase. Reductions in phytic acid P ranging from 50 to 65% with no decreases in TP of the seed were seen in ‘low-phytic acid’ or ‘high-available P’ (HAP) mutants when phytase supplementation was contained in diet. However, total activity of phytase was 35% higher in the small intestine of laying hens because of different pH. And both microbial phytase and lactic acid enhanced the apparent total tract digestibility (ATTD) of ash, Ca and Mg and apparent ileal digestibility (AID) of phytic acid.

Production of poultry in the Lao People's Democratic Republic is described. Data from field surveys and from Government and other documents are analysed. Some 95 per cent of poultry are kept in the village, mainly scavenging, system and only 5 per cent are found in industrial systems. Poultry (domestic fowl, two duck species, turkey, Chinese goose, pigeon and other species in that order of importance) are kept by about 90 per cent of households. In absolute terms greatest numbers are found in the northern and central parts of the country. More birds per person are kept in the less developed northern and southern regions. “Average” households own a mixed flock comprising 14–20 domestic fowl, 6–10 ducks, 2–6 turkeys and geese and a flock of pigeons although most owners raise only fowl and ducks. Genetic resources are almost entirely indigenous or naturalized except for a relatively small number of hybrid domestic fowl for industrial egg and meat production. National poultry meat production in 2000 was estimated at 12 800 tonnes and egg production at 10 700 tonnes. Production per bird is 25–60 eggs per year for scavenging fowl and common Anas ducks and slightly less for Muscovy ducks. Village poultry products are consumed at home or sold in local markets. There is growing urban demand from which small scale producers should be able to benefit. Disease is an important constraint to production. Newcastle disease is the main problem in village flocks. Avian Influenza is of concern in the commercial sector. More attention should be given to smallholder producers. This, together with interventions in housing and sanitation and in nutrition and disease control, would greatly increase output. Smallholder producers would be the principal beneficiaries of these interventions in improvements to food security and nutritional status and in reduced production risk.