Broilers in the New Millennium

The broiler chicken industry has grown consistently over its 40-year history. Today 40 million tonnes of eviscerated chicken carcasses are produced annually. This represents 29 per cent of meat production from farmed animals. The growth is based on strong consumer demand for products that are perceived as affordable, safe and healthy. Improving economic efficiency has been driven by rapid genetic change. this is delivered through a short and efficient multiplication process. Genetic improvement in growth rate of up to three per cent per year requires major adjustments to how the birds are managed to benefit from the extra genetic potential.

The industry has experienced periods of increased incidence of defects in skeletal development  and heart and lung function. Genetic and management solutions have been applied to these problems. Systems have been developed to anticipate adverse genetic-correlated response in the future, allowing early genetic management changes.

Genetic Change

The current broiler male grows to 2.6 kg in 42 days with a feed conversion ratio (FCR) of 1.66. The live bird yields 1.85kg (71 per cent) as eviscerated carcass and the total meat yield is 875g (33.7 per cent) and breast meat yield is 460g (17.8 per cent).

Annual improvement rates are an increase of 60g of live weight to 42 days (2.4 per cent), a reduction of FCR by 0.02 to 2 kg (1.2 per cent) and an increase of breast yield of 0.25 per cent (1.4 per cent).

Progress is measured by actual field performance, performance in trials facilities and also relative to lines established 1972 (broilers 1976). Live weights at 42 days have more than doubled in the last 23 years (from 1050g to 2600g) and are projected to reach 3 kg by the year 2007 at current rates of progress. The time to achieve 2kg (a common killing weight) has been reduced from 63 days in 1976 to 36 days. This will decline more slowly in future because of high daily growth rates. By 2007, birds will reach 2kg in 33 days. FCR to fixed ages and weights continues to improve with growth rate but must eventually be limited. Breast meat yields continue to increase as a percentage of live weight at a wide range of killing ages and weights. A 2kg male in 1976 yielded 250 g of breast meat whereas today it yields 340 g and is projected to yield 380 g by 2007. The economic impact of these improvements can be illustrated by the ratio of the weight of feed required to produce 1kg of breast meat. This was 20kg/kg in 1976, but has been reduced to less than 10kg/kg at present and will approach 7kg/kg by the year 2007.

Adverse Effects of Genetic Change

Genetic change of such a magnitude inevitably has an impact on all aspects of the birds’ physiology. These have to be accommodated by improvements in many aspects of the management of birds kept for reproduction or growth.

For example, the industry has evolved sophisticated and successful methods of managing growth of breeding stock to optimize livability, immune function and chick production. The impact of rapid growth on two aspects of physiology—skeletal development and heart and lung function—has come under particular scrutiny.

An increasing incidence of lameness in the 1980s was mainly due to tibial dyschrondroplasia. This is a dysfunction of the growth plate of the tibia and its incidence was affected by many factors in the environment, especially mineral nutrition and lighting programs (Whitehead, 1992: Thorpe, 1994). These findings have led to significant changes in management practices.

Continued research is aimed at establishing the changing mineral requirements of genetically improved birds. A number of improvements have been made in selection programs to reduce the incidence of defects in the growth plate.

These include better use of family information and the detection of subclinical lesions in the growth plate by real time X-ray technology. It is essential to improve heart and lung function as growth rates increase. Ascites was first observed in birds grown at high altitudes but the incidence began to increase at all altitudes during the 1980s.

It is due mainly to pulmonary hypertension, cardiac pathologies or cellular damage caused by reactive molecules (Currie, 1999). A wide range of environmental factors affects the incidence. The most obvious of these are poor ventilation, high dust levels, high diurnal temperature variation, infectious agents, toxins and deviations from optimum nutrition.

All of these issues have been addressed in research and have been applied very quickly to production flocks. The genetics of ascites resistance has been an active research area in all breeding companies. A range of technologies has been applied including improved family selection, selection in a predisposing environment, pulse oxymetry and other measures of heart and lung function.

The intention in both cases is to improve robustness of the genotypes to the variations of the environment and to make producers aware of the important environmental variables.

Future Strategies

Continued selection progress will include closer monitoring of phsyiological systems to ensure a closely integrated response to multiple traits. These already include aspects of immune function and reproductive performance.

Feedback systems are in place that give early warning of performance, welfare, environmental impact or food safety issues from producers in a wide range of environments.

Presented at the Poultry Industry Council Poultry Health Conference in Kitchener, Ont.