The feeding value of sorghum for poultry has been a subject of study for many years. Of particular interest has been tannin, an antinutritive factor present in some sorghum cultivars, its influence on bird performance and means of alleviating its effects. This paper briefly discusses antinutritive factors in feedstuffs and reviews in detail the literature on the deleterious effects of sorghum tannins on various performance parameters and on the detoxif ication methods that have been tested. Inconsistencies in the literature are highlighted.

The results from experimental studies about genetic factors (‘major genes’) involved in disease resistance and their effects in different genetic backgrounds are reviewed and discussed. The major genes considered are (1) Tv-A and Tv-B, gene loci controlling resistance to infection from avian leukosis virus (ALV), (2) B blood groups which represent the major histocompatibility complex (MHC) of the domestic fowl and are indicators of genetic differences in resistance to Marek's disease (MD) and, only tentatively, (3) endogenous viral (ev) genes which can influence reactions to leukosis infection. For these experiments purebred and crossbred progeny from three genetically different experimental White Leghorn lines have been used extensively. The results concerned with leukosis are based on a comparison between groups of chickens which were homozygous resistant or susceptible to ALV infection. The variability in the amount of damage from leukosis points to interactions between the genotype of resistance to ALV infection and genetic characteristics of the line or lines involved. In this respect the negative influence of ev 6 on the immune response to ALV infection could play a role. To study the association of B blood groups and resistance to MD, an experimental line which still segregated at the B locus (B2, B13, B14 and B21) was crossed with two other lines which were homozygous, respectively, for B2 and B15. Mortality caused by MD in birds carrying the same segregating B blood groups showed a completely different pattern in the two crosses. Rather unexpectedly, the difference in MD mortality was largest between the two types of crossbred layers carrying B21, which points to an interaction between line and B blood group type. Further studies suggested that this interaction depends on genes within the MHC for which the lines crossed might differ. The availability of information from different genetic groups allowed an evaluation of the importance of each ‘major gene’ in relation to the comparative effects of other factors influencing the trait under consideration. Apart from becoming aware of possible interactions resulting from genetic differences between lines, simultaneous results from genetically different experimental lines also provide a safeguard against overestimating or underestimating the potential of such ‘major genes’ for practical utilization in poultry breeding.

The main objective of this review is to present the advantages and disadvantages of applying the best linear unbiased prediction (BLUP) procedure with an animal model to the evaluation of laying fowl within a breeding programme. Following an outline of the traditional selection index-based procedure there are descriptions of mixed model methodology including modelling and data transformation, genetic parameter estimation and breeding value prediction. Some computer programs for carrying out BLUP animal model algorithms are described and the results of empirical and simulation comparisons involving different livestock species are given. New possibilities arising from the application of the animal model to breeding strategy are discussed. Poultry breeding evaluations using the traditional selection index do not always result in the same conclusions as arise when using BLUP. However it seems likely that, as has happened with other livestock species, the BLUP animal model method will be increasingly applied in breeding programmes to improve egg production.

An ability to alter sex ratio could be enormously beneficial to the poultry industry. As a consequence, there has been increasing scientific interest in avian sex determiniation and sexual differentiation. Recent progress in avian cytogenetics and molecular biology has enhanced understanding of the mechanisms involved. Surgical and endocrinological techniques have been used to reverse sexual differentiation. Mixed sex chimeras, containing both male and female derived cells and produced by embryo engineering, can be used as a novel model for sexual differentiation. A combination of new knowledge and the refinement of techniques could open up new frontiers for the advancement of our understanding of sexual regulation in poultry.

Dietary flax seed may prove to be a key feed ingredient in establishing the egg as a food useful for promoting cardiovascular health in humans. Yolk linolenic acid (LNA; 18:3n−3) increases in a linear fashion in response to graded levels of ground flax seed and whole flax seed if grit is provided in the feed to promote in vivo seed grinding. In contrast, the metabolic derivatives of LNA, eicosapentaenoic acid (EPA; 20:5n−3) and docosahexaenoic acid (DHA; 22:6n−3), are deposited only in limited amounts regardless of the level or form of flax seed fed. The distribution of the omega-3 polyunsaturated fatty acids (n−3 PUFA) in egg yolk lipid classes varies between laying stocks and these differences appear to influence the oxidative and sensory qualities of the product. Dietary flax seed results in apparently benign fluctuations in body weight of mature laying hens. Undesirable changes in egg production have only been reported for young birds early in their reproductive cycles. Changes in egg quality include reduced shell weight and decreased yolk weight. It is proposed that yolk weight reduction is related to changes in circulating oestradiol brought about by either n−3 PUFA or the phyto-oestrogens characteristic of flax seed.

Broodiness or, more precisely, incubation behaviour, results in the regression of the ovary and in lost egg production. It is a particular problem in turkeys and broiler breeders and may become more of a problem for other types of poultry if ‘welfare friendly’ husbandry systems become more widely used. Any system that allows the expression of full nesting behaviour will encourage the development of broodiness. The incidence of broodiness can be reduced in three ways: changing the genotype, manipulating the environment and by administering veterinary products to alter hormone function. The first two methods are generally employed, but are costly. While the third approach has not proved to be commercially viable, the situation may change. Recent advances in understanding the hormone control of broodiness have led to the identification of two novel potential veterinary products for immunization against broodiness. The first is based on the observation that an increase in the secretion of the pituitary hormone, prolactin, causes broodiness. The prolactin gene of the domestic fowl has been cloned and used to produce recombinantderived prolactin. This has been used successfully to immunize domestic fowl against broodiness, without compromising a high rate of egg laying. The second immunological approach is based on the identification of the avian prolactin releasing hormone as vasoactive intestinal polypeptide (VIP). This 28-amino acid neuropeptide was originally isolated from the gut. Immunization against VIP suppresses prolactin secretion and inhibits the development of broodiness while maintaining a high rate of egg laying. It is concluded that two novel immunogens – recombinant-derived prolactin and vasoctive intestinal polypeptide – are effective in suppressing broody behaviour and are available for further development as practical veterinary products.

Betaine, a donor of labile methyl groups, can spare choline and methionine but cannot replace these compounds in poultry diets. Betaine is synthesized from choline by choline oxidase and it can donate methyl groups to homocysteine to form methionine. Physiologically, betaine is one of several compounds used by cells to regulate osmotic pressure. Among the potential benefits of its inclusion in poultry feeds are sparing choline, carcass fat reduction and aiding cell osmoregulation. Some feed ingredients are natural sources of betaine per se. This review considers the metabolism, functions and applications of betaine in poultry.

In recent years the incidence of avian cellulitis (inflammatory process, IP) has risen dramatically so that today it follows septicaemia-toxaemia as the second leading cause of broiler carcass condemnation. Affected birds frequently appear as large, healthy and normally growing, but exhibit caseous mats called plaques under the skin at processing. Affected flocks increase costs to processors from direct product loss, downgrading and yield loss due to trimming and the slowing of processing lines. Although a number of bacterial species have been isolated from cellulitis lesions, Escherichia coli is most consistently recovered. This review examines past and present scientific and popular press literature on cellulitis and attempts to separate opinion from scientifically verified and tested fact.

Non-destructive methods for assessing egg quality are used in the egg industry and in research on avian embryogenesis, incubation, selection programmes, genetics etc. According to the purpose for which they are being used, non-destructive methods have to meet certain requirements – rapid estimation of the results in the case of industrial use and high significance when used in research. In both cases minimum measurement of the initial parameters is preferable. In this review methods are considered that allow calculation of such egg variables as volume, surface area, shell weight, shell volume, shell density and thickness; weight, volume and density of egg contents; yolk and albumen weights; Haugh unit score and consistency of the interior; and strength characteristics of an egg that keep it intact.

Skeletal integrity of end-of-lay birds is becoming a major concern for both egg producers and meat processors. Osteoporosis induced by continual demands for shell calcification causes loss in skeletal integrity as the layer gets older. This loss in bone structure, coupled with minimal exercise, leads to very fragile bones in older birds. Bone breakage as high as 20% has been reported in birds entering the processing plant, while some degree of bone breakage is found in a much higher proportion of eviscerated carcasses. Bone breakage on the farm, during transport and subsequent handling is obviously a welfare concern, while processors are also concerned about bone contamination of meat products. Factors affecting the development of osteoporosis are discussed and include genetics, level of egg production, environment and nutrition. There is no simple solution to the problem in terms of long-term or short-term nutritional modification. In the case of caged birds, bone strength characteristics can be improved by removing them to other systems for a period of time prior to transport, although this is rarely a commercial solution. However, so-called alternative housing systems are themselves responsible for skeletal defects in some birds.

A number of major influences that will affect the formulation of poultry diets in the decades ahead are considered. Their impact will be mediated by the changing structure of the poultry industry where vertical integration, especially in the case of poultry meat, is a dominant feature. This forward looking review focuses on the impact of the health conscious consumer seeking foods with desiable characteristics, particularly in terms of the types and content of fatty acids; the need for increased antioxidant content of products to help enhance quality and shelf life; the potential for improved dietary composition of poultry feedstuffs to promote stock health; the use of enzymes to enhance nutrient availability and neutralize antinutritional factors in some feedstuffs; and the potential for new feed raw materials, including crops with genetically enhanced nutrient composition.

This paper reviews recent advances on the use and mode of action of probiotics (direct-fed microbials) in poultry. The addition of probiotics to the diet has been found to improve growth performance and feed conversion in broilers, and egg mass, egg weight and egg size in layers. The mode of action of probiotics in poultry includes (i) maintaining normal intestinal microflora by competitive exclusion and antagonism; (ii) altering metabolism by increasing digestive enzyme activity and decreasing bacterial enzyme activity and ammonia production; (iii) improving feed intake and digestion; and (iv) neutralizing enterotoxins and stimulating the immune system.

An imbalance in the human dietary intake of various types of fatty acids has become apparent. Results of fundamental studies have shown specific and beneficial effects on human health and well-being through the consumption of the long chain n-3 polyunsaturated fatty acids, in particular eicosapentaenoic acid and docosahexaenoic acid, which play an important role in rectifying this imbalance. As a result of these observations, recent recommendations pertaining to the consumption of dietary fat have stressed the importance of consuming higher levels of these fatty acids. In addition to increasing oily fish consumption, intake of the n-3 polyunsaturates can be enhanced through the consumption of commonly occurring non-fish foods containing elevated levels of these fatty acids. The fatty acid composition of the lipids of avian egg yolk and muscle tissues may be modified to match human nutritional guidelines better by appropriately manipulating the fatty acid composition of the diet; for example, modifications of the avian diet have raised total n-3 fatty acid content in egg yolk to over 200mg. Beneficial effects on blood lipoprotein characteristics in humans who consumed eggs with such modified fatty acid contents have been recorded. As in the case of eggs, meaningful quantities of n-3 polyunsaturates have been incorporated into major poultry muscle tissues. Concerns have been expressed over the development of unacceptable odours in eggs and meat from birds fed diets with increased polyunsaturation. However, by using only high quality materials, limiting the amount of fish oil or fishmeal within the diet and optimising the provision of supplemental dietary antioxidants, the production of eggs and meat with increased n-3 polyunsaturates is practicable.

This paper considers some of the factors affecting the fertility and hatchability of guinea fowl eggs. In addition to genetic components there is a wide range of environmental influences that affect these two measures of performance. These include severe nutritional deficiencies, certain drugs and feed contamination with pesticides and mycotoxins. After eggs are laid, faulty handling and storage conditions and incorrect fumigation procedures have harmful effects on hatchability, while correct incubation temperature, humidity and ventilation rates during the setting and hatching stages are essential for optimum results. The causes of low levels of hatchability can be identified by the careful examination of eggs which fail to hatch. However, accurate and complete records relating to the breeder flock and the history of the eggs from the nest through to the completion of incubation are essential for problem solving and in helping to obtain optimum results.

Rare earths (RE) is the common name for the metallic elements of the lanthanide series, together with yttrium and scandium, which make up 0.016% of the earth's crust. This review summarizes the results of experiments conducted in China in which RE were added to poultry diets. Additions of 30–1000mg/kg RE to layer diets resulted in increases in egg production of 3–15% and improved feed conversion efficiency of 2–22%. The hatchability of eggs increased by 5–15%. Improvements of 4–14% in body weight gain were observed in broilers fed 20–400 mg/kg, together with 3–6% better feed conversion efficiency and increases of 3–5% in eviscerated yield. Similar benefits have also been reported when feeding RE to ducks, although not statistically validated, and to meat-type pigeons. No adverse effects of feeding RE have been reported. It is concluded that rare earths have a role as feed additives in the poultry industry, particularly in conditions where the genetic potential for production traits is not achieved. Key information from some of the papers cited in the paper is summarized in an appendix.

The present state of the art of biological/physiological research on poultry is described with special emphasis given to future direction. Public policy issues related to agricultural research are considered, including funding, and questions related to the balance between fundamental and applied research and to competitive grants are addressed. The view is espoused that there should be a balance between fundamental and applied research and that this research should have high scientific quality, with relevance to the problems of the industry, and impact on their solution. This is best achieved with a portfolio of research projects ranging from disciplinary to multidisciplinary. In the belief that there needs to be a scientific infrastructure that provides mutual support, and hence improved productivity, a plea is made for greater communication and tolerance among scientists in different fields.