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.

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.

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.

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.

Vitamin A is an essential nutrient that has an influence on immune responses in birds. Both low and high vitamin A intakes result in impaired immune responses. Low dietary vitamin A has been shown to cause reduced antibody production, defective T-cell responses and reduced phagocytosis, and decreased resistance to infection by bacterial and viral pathogens and protozoan enteropathogens. Enhanced immune responses can be elicited by high, but not excessive, dosages of vitamin A. Optimum immune responses in growing chicks and turkeys were obtained with vitamin A intakes that were 3–10 fold higher than NRC recommended levels.

Since 1969 the Hungarian Upgraded and Gray Landes breeds of geese have been improved at the Goose Breeding Research Station of Gödöllö University of Agricultural Sciences at Babatpuszta. An overview of 15 years history of these two breeds shows an average annual increase in egg production of almost one egg and average annual improvements of 1% in fertility and one day old gosliings per year. These improvements are attributed to the results of selection carried out between 1978 and 1992.