Many studies have shown that saline drinking water supplied to mature laying hens at concentrations similar to those found in underground bore water has an adverse effect on eggshell quality and on the incidence of eggshell defects. This response can be observed in the absence of any adverse effects on production parameters such as food intake, egg production and egg weight. Strain differences appear to exist, and even within a strain there is considerable variation in the responses of individual hens to saline drinking water. The sensitivity of the hen also increases with age with a greater occurrence of broken and shell-less eggs. The incidence of shell-less eggs also increases with higher concentrations of NaC1 in the water. The use of saline drinking water with breeder flocks significantly reduces the production of day-old chicks through reduced numbers of settable eggs and lower hatchability. The primary metabolic lesion associated with the poor eggshell quality which results from the intake of saline drinking water appears to be related to the supply of bicarbonate rather than calcium to the lumen of the shell gland for eggshell formation. A reduced activity of carbonic anhydrase in the shell gland mucosa is of particular importance. This limits the supply of bicarbonate and the dependent calcium to the lumen of the shell gland. Treatments which have been found to be effective are preventive rather than remedial in nature. The two most promising treatments, apart from desalination of drinking water, appear to be the use of ascorbic acid supplements in the diet or drinking water appear to be the use of ascorbic acid supplements in the diet or drinking water and the use of zinc–methionine supplements in the diet. The mechanism by which ascorbic acid exerts its effect is unknown but the response is dose-dependent. The zinc component of zinc–methionine appears to be the important factor with this treatment, perhaps through its effect on carbonic anhydrase, a zinc-requiring enzyme.

Irradiation offers a potential method for effective microbial control of poultry feed. Birds fed such irradiated diets are not adversely affected and radiation status of the diet is unchanged. While radiation at 25–35 kGy is likely to raise feed temperature by only 5°C during processing, there seems to be loss in potency of certain nutrients. Most reports indicate loss in potency of all fat-soluble vitamins, and there are less consistent reports regarding thiamine and pyridoxine. At 25–35 kGy irradiation there will be around 15% loss of potency of these vitamins. Irradiation also causes increased peroxidation of fats, although this effect can be controlled by appropriate inclusion of antioxidants. There are no consistent reports of irradiation having any effect on protein quality or amino acid status of diets.

The major histocompatibility complex (MHC) is a group of genes present in all vertebrates. The chicken MHC is broken into three distinct regions, each of which codes for certain gene products. These antigens are known to influence a variety of biological functions including fowl cholera, Marek's disease, Rous sarcoma virus, lymphoid leukosis and coccidiosis. Fertility, embryonic mortality, hatchability, and egg production are some of the production parameters linked to this gene complex. Blood groups serve as markers for these regions, offering a means of genetic screening.

The sources and factors by which poultry house dust and gases are generated, the levels encountered and their effect on the respiratory health of stockmen are reviewed. Although exposure to aerial pollutants in intensive housing can lead to respiratory disease, the mechanisms involved in this process are poorly understood. These mechanisms and the dynamics of the micro-environment involved in the generation of dust and gases from poultry litter are discussed. From the limited knowledge available, only partially effective methods of dust and gas control are possible.

Although still in the experimental phase, the technique of freezing domestic fowl semen may prove of interest and value to the industry. Various stages of the application of this method of preservation still need to be improved. One of the most critical aspects is the choice of cryoprotectant and its use during the process of freezing and thawing. While glycerol has a better cryopreservative action than other cryoprotectants in domestic fowl semen, it exerts a widely demonstrated contraceptive action, the mechanism of which has not yet been clarified. Thus the use of glycerol as a cryoprotectant must be accompanied by its complete removal before insemination.

The fertilizing capacity of semen preserved by freezing is notably less than that of fresh (non-preserved) material and has been evaluated as 1.6% and 19.7%. Genetic influences appear to affect spermatozoan response and tolerance to thermal treatments resulting in differences in subsequent fertility. Most studies using fowl semen report final freezing temperatures between –79°C and –196°C, a cooling rate of 1–10°C/minute and a thawing rate of 50–70°C/minute.

Straws have been found to be more satisfactory containers than glass vials or ampoules for preserving semen from domestic fowl.

In the UK the poultry industry has a good record with regard to surface water contamination and has been responsible for only a small proportion of the total pollution incidents attributable to agriculture. Guidance is provided to farmers by a Code of Good Agricultural Practice for the Protection of Water. Because poultry manures have high concentrations of total nitrogen, with much of this in soluble form, the pollution of ground water with nitrates is a more serious problem. A voluntary Pilot Nitrate Scheme has been introduced in some parts of the UK which controls the quantities of animal waste applied to the land and also the timing of waste application. Linked to the scheme is a comprehensive programme of scientific monitoring. The broad requirements of the European Community Nitrate Directive are described. In the case of air pollution due to odours, poultry farms were reported to be responsible for 17% of complaints attributed to agriculture. Where appropriate, legislative means exist to reduce the nuisance and a Code of Good Agricultural Practice for the Protection of Air has been published. Some implications for poultry production in the future are considered.

In the Netherlands the high densities of farm livestock pose a number of problems, particularly with regard to waste disposal. Nitrogen compounds leaching out of animal waste form one of the most serious environmental contaminants. Modified housing systems, such as the use of plastic netting floors for broilers (which speeds up dehydration), often can largely eliminate the release of ammonium gas which gives rise to air pollution. However, this only defers the problem because subsequent application of the droppings to the land, where they become rehydrated, results in the rapid production of ammonia and nitrates through microbial activity. Research at Delft University identified bacteria capable of converting the nitrogen in ammonia to molecular nitrogen gas under aerobic conditions. Subsequent development work at the Spelderholt Institute has established a considerable potential for application. The addition of cultures of the bacteria to the feed is a promising future technology.

In the UK about 1.4 million tonnes of used poultry litter are produced each year. Its disposal by direct use as a fertilizer or by landfill can, in some circumstances, have an adverse environmental impact. Waste-to-energy schemes which generate revenue from the energy produced and may provide fertilizer as a valuable byproduct offer an alternative and environmentally acceptable means of disposal.