When formulating least-cost poultry diets, ME concentration should be optimised by an iterative procedure, not entered as a fixed value. This iteration must calculate profit margins by taking into account the way in which feed intake and saleable outputs vary with ME concentration.

In the case of broilers, adjustment of critical amino acid contents in direct proportion to ME concentration does not result in birds of equal fatness. To avoid an increase in fat deposition at higher energy levels, it is proposed that amino acid specifications should be adjusted in proportion to changes in the net energy supplied by the feed. A model is available which will both interpret responses to amino acids in laying trials and give economically optimal estimates of amino acid inputs for practical feed formulation. Flocks coming into lay and flocks nearing the end of the pullet year have bimodal distributions of rates of lay, with the result that calculations of requirement based on mean output will underestimate the optimal amino acid input for the flock.

Chick diets containing surplus protein can lead to impaired utilisation of the first-limiting amino acid. This difficulty can be avoided by stating amino acid requirements as a proportion of the protein.

Chicken gene inheritance analysis, started one century ago, had led to the development of the classical genetic map. Efforts and legacy of the previous geneticists' generations are not forgotten and constitute the fundamentals of contemporary genome research progress. Advances in molecular biology, cytogenetics and DNA technologies provided more powerful and sophisticated tools to tackle chicken gene mapping and genome research problems. In the 1990s configurations of chicken molecular and cytogenetic maps had begun standing out. New horizons in chicken genomics are opening with application of BAC libraries, BAC-contig physical maps, ESTs and whole genome sequencing. The chicken has been a notable experimental model for several fundamental and applied biologic disciplines in the last century, and will remain such in the 21st century. The upcoming complete genome sequencing combined with discovering gene functions will facilitate the improvement of traits of economic importance and value in poultry.

Feather growth, structure and patterns of moulting are important characteristics of poultry in commercial environments. As the market age for broilers continues to decline, the “maturity” of feather cover becomes even more important for protection of the skin and underlying tissue. Feather growth begins at around day 5 of incubation while keratinisation is complete 2 – 3 d prior to hatch. Feathers do not grow randomly over the skin surface, but rather in distinct tracts, which cover at most 75% of the skin surface. Broiler chickens will have about 50 g of feathers by market age, although at this early age some feathers will have already been lost by sequential moulting. Although most modern strains of poultry have white or brown feathers, there are various colour schemes that are again dictated during embryo development. In a subsequent paper, we will detail factors affecting feather growth, moulting and the Occurrence of various abnormalities.

In commercial production, there is often concern about the quantity and/or quality of feathering in both broilers and layers. For broilers, the concern is adequacy of protective feather cover, while in layers it is usually the necessary degree of feathering needed to optimise feed efficiency. Feather development is under the control of hormones such as thyroxine and oestrogen and indirectly by testosterone. Environmental or nutritional status that influences such hormonal output will indirectly affect feathering. In broilers, rate of feathering is influenced by genetics, since some 20 years ago there was a conscious decision to introduce slow (K) vs. fast (k) feathering as a means of sexing day-old chicks. With the relative “immaturity” of modern broilers, these genes influence feather cover well into the production cycle. In White Leghorn crosses, initial problems with apparent Leukosis susceptibility of the progeny of slow feathering dams had to be overcome by eradication of Leukosis before feather sexing could be generally introduced. Nutrition can influence rate of feathering as well as feather structure, colour and moulting. Amino acid balance and especially deficiencies of TSAA and branched chain amino acids will influence feathering in young birds. Deficiency of vitamins and certain trace minerals also induce characteristic feather abnormalities, as does the presence of dietary mycotoxins. A number of viruses, bacteria and mycoplasma can infect the feather follicle and so influence feather development. Feather pecking and feather licking are behavioural abnormalities, although these conditions can be induced by changes in environmental conditions or nutritional adequacy of the diet.

The control of excreta/litter moisture and quality is a priority in the modern poultry industry, to avoid environmental and animal welfare problems and to reduce productivity losses. Control implies the reduction of their amounts and moisture content. Several factors can affect them, some related to management and housing, others related to diseases and finally, dietary factors. The paper reviews some nutritional aspects that could interfere with the moisture and quality of poultry excreta/litter, focusing on dietary factors affecting water consumption, water excretion and the amount and composition of excreta: dietary protein level, electrolyte balance, ionophores, cereals causing viscosity problems or containing high levels of non-digestible fibre fractions, unusual ingredients or by-products and finally some feed technological treatments.

Reasons for starch digestibility variations are reviewed by considering starch granule structure, antinutritional factors and access problems in coarse particles. Feed technology treatments that can overcome low starch digestibilities are also reviewed. Before considering these factors, the particular features of the digestive system of chickens are briefly reviewed.

The digestive system of chickens for starch hydrolysis is characterised by a high enzymatic potential. However, in contrast with mammals, the potential of chickens for completing starch digestion by microbial degradation in the distal part of the digestive tract is very low.

Variations in starch granule structure especially concern legume seeds compared to cereals, with greater resistance observed for the former. Plant mutants may result in variations in amylose contents of starch granules. Those with high amylose content (70%) produce low starch digestibilities. Cereals with no amylose (waxy starch) do not show strong evidence of benefit despite lower resistance of starch granules.

In practical conditions, antinutritional factors such as proteinaceous α-amylase inhibitors, condensed tannins and viscous water-soluble non-starch polysaccharides generally result in low effects on starch digestibility. However, viscosity may induce a noticeable effect with high viscosity barleys. There is much less evidence that viscosity can explain the low starch digestibilities (<94%) which are observed with some wheat samples. Positive effects of enzyme additives on starch digestibility of cereals probably result from effects both on viscosity and on disruption of coarse particles.

Access problems in coarse particles are responsible for low starch digestibilities observed with legume seeds. However, mechanical treatments such as fine grinding and pelleting can readily overcome this problem. Access problem in coarse particles is also probably the reason that explains low starch digestibilities in some cereal samples, as shown by negative relationships between hardness and starch digestibility of wheats. However, grinding and pelleting of cereals seem to be less efficient than with legume seeds. Interactions with feeding behaviour and genetic origin of birds have also to be considered for explaining variations in starch digestibility of cereals.

Interactions between nutrition and immunity are diverse and have profound implications on animal growth and productivity. The innate immune system provides protection during the initial stages of infection and is responsible for mediating many of the alterations in nutrient metabolism. The macrophage is the key sensory and regulatory cell of the innate immune system. Their pro-inflammatory cytokines coordinate local immunity to pathogens, yet also act systemically to alter metabolic homeostasis and decrease food intake and growth rate. Altered energy, amino acid, lipid, and mineral metabolism have nutritionally important implications. For example, an innate immune response results in decreased uptake of amino acids by skeletal muscles and a corresponding increase in uptake by the liver and to a lesser extent by leukocytes. The net result is a decrease in amino acid requirements with no change in the efficiency of their use for growth. The shift in the priority of individual tissues for nutrients appears to be accomplished by changes in the types and amounts of their nutrient transporters and storage proteins. Adaptive immune responses result in considerably more subtle changes in nutrient metabolism than innate responses.

Several factors may limit the development and viability of late-term embryos and hatchlings: 1 The nutrient content of the egg needed for the development of tissues and nutrient reserves (glycogen, muscle, yolk) of the embryo through to hatch; 2 The ability of the gastrointestinal tract to digest utilize nutrients from an external carbohydrate and protein-rich diet; and 3 The ability of chicks and poults to rely on the residual nutrients in the yolk sac during the first few days post-hatch. These limitations are manifested by in the “chick or poult quality” phenomena. Approximately 2% to 5% of hatchlings do not survive the critical post-hatch “adjustment” period and many survivors exhibit stunted growth, inefficient feed utilization, reduced disease resistance, or poor meat yield. These limitations can be alleviated by the administration of food in the hatchery immediately post-hatch, a technology termed “Early Feeding”, or by administration of food into the amnion of late term embryo, what we define as “In Ovo Feeding”. A great potential exists in “combining” the early feeding and the in ovo feeding methods. Since the modern broiler increases its body weight by 50-fold from hatch until market age at 42 days, the first few critical days of “adjustment” represent a much greater proportion of the bird's life span than in the past. Consequently, early feeding methods will have a great impact on overall growth and well-being of the bird, particularly as genetic selection for increased growth performance continues in the future.

Contamination of poultry meat products with Salmonella and Cumpylobucter spp. continues to be the main microbiological problem affecting both industry and consumers. In some countries, control measures appear to have reduced flock infection with Sulmonella, but other issues have arisen; these include an increase in multiple resistance to antimicrobials in certain serotypes and the recent emergence of S. Paratyphi B variant Java, also frequently multi-resistant. For intensive production systems, there is much information on sources and routes of Salmonella transmission and the relative risk of infection/contamination at different stages of production. Some possible reasons for control failures are discussed. In contrast, less is known about Campylobacter in these respects, and a better understanding is needed of the physiology and host-interactions of the organisms, and of their behaviour in poultry operations. On such knowledge may depend the future development of effective controls.