The genetics of modern commercial poultry
By James C. Mckay
By James C. Mckay
The genetics of modern commercial poultry
Improvements in health, nutrition and environmental management have contributed to the dramatic improvement in performance of commercial poultry since the 1950s.
JAMES C. MCKAY,
EW Group, Lochend Road, Newbridge, Midlothian EH28 9SZ, U.K.
Improvements in health, nutrition and environmental management have contributed to the dramatic improvement in performance of commercial poultry since the 1950s, but the majority of the improvement can be attributed to genetic factors. Egg production has been improved consistently over seventy years and the industry continues to improve the efficiency of production by at least 1 per cent per year. In broilers, combined selection for growth, body composition, feed efficiency and livability continues to deliver 2-3% improvement per year in the efficiency of meat production. Sustainable genetic programs must manage genetic resources for long-term improvements and give high priority to the health and welfare of the stock. Improving efficiency of production reduces the overall environmental impact of poultry production and improves the sustainability of the industry. Disease challenges can have a major impact on efficiency but improvements in vaccination, nutrition and biosecurity have contributed to improved livability and welfare. Continuing genetic improvement in disease resistance will be an important component of future genetic programs. The ethics of animal breeding is an important issue. Genetic improvement programs are designed to continue improving animal welfare, animal health, food safety, environmental impact and economic performance.
Poultry have been domesticated for thousands of years and man has made many genetic changes during the process of domestication and since then by establishing local varieties and selecting for various traits. The genetic progress made in the last fifty years has been the foundation of a modern poultry industry that is a major source of animal protein in most countries of the world. The history of poultry domestication and the development of a modern poultry industry are well reviewed (Chambers, 1990). Recent developments in knowledge and technology have changed the dynamics of poultry breeding.
II. THE MODERN POULTRY INDUSTRY
The production of poultry meat and eggs is a world-wide industry which supplies at least one third of animal derived food for the 6 billion people on earth. The statistical service of the Food and Agriculture Organisation records that in 1961 the world produced less than 10 million tonnes of poultry meat. By 2006 the worldís production of poultry meat was 81 million tonnes. This represents a compound annual growth rate of more than five per cent. Poultry meat production has increased every year since FAO records began. In 1965 the world produced less than 5 kgs of poultry meat per capita and 45 years later we produce more than 13 kgs per capita. The vast majority of the meat (70 million tonnes) is produced by broiler chickens with the remainder produced by turkeys (5 million tonnes), ducks (3.5 million tonnes) and geese and others (2.5 million tonnes). The production of 71 million tonnes of chicken meat requires and annual crop of at least 40 billion broilers.
The world’s egg production has also increased steadily throughout this period growing from 15 million tonnes in 1961 to 60 million tonnes in 2006, an annual compound growth rate of 3 per cent. This represents an annual production of at least one trillion eggs (one times ten to the power 12) and these are produced by a population of approximately 6 billion layer hens (one times ten to the power nine). There are as many layer hens as there are people in the world today. In 1965 we produced 5 kgs of eggs per capita and today we produce more than 10 kgs per capita. Ninety two percent of the world’s eggs are produced by layer chickens with ducks geese and other species making up the rest.
The development of such an industry has required coordinated improvements of technologies in a number of areas. The most significant improvements have been in:
1) Environmental control. Controlled environment housing has ensured safety from predation, more predictable production and improved biosecurity.
2) Nutrition. The nutritional requirements have changed as birds have been selected for efficient production.
3) Poultry health. The development of effective vaccines and therapeutics, improved biosecurity and better nutrition have all contributed to improved health. The emergence of breeding companies which are able to supply stock reliably free of the major vertically transmitted pathogens means that replacement stock can always be of a high health status.
4) Genetics. There has been consistent selection for improved productivity and quality.
III. THE CONTRIBUTION OF GENETICS
Improvements in health, nutrition and environmental management have contributed to improved performance but the majority of the change has been attributed to genetic improvement. Havenstein et al (2003) compared the performance of contemporary broilers and a line random bred since 1957. They estimate that at least 85% of the improvement in performance is attributable to genetic changes. In broilers combined selection for growth, body composition, feed efficiency and continues to deliver 2-3% improvement per year in the efficiency of meat production. Other traits such as robustness, specific and general disease resistance and absence of metabolic defects have also contributed to this progress (Aviagen data).
In production environments the data also show clear genetic trends. For example in the United States their Industry Reporting Service, which records the performance of the majority of the broilers produced there, shows that over the last five years growth rates have improved by 0.74 days per year for broilers grown to 2.27 kg. Breast meat yields have improved by 0.5 per cent per year and FCR is decreasing by 0.025 per year. The combined improvements in growth, yield and efficiency mean that the overall efficiency of meat production is improving by more than 3% per year. Even with such improvements in growth and efficiency, the live ability of broilers is improving by 0.22% per year and the condemnation rates have fallen by 0.7% per year over this period. This outcome requires combined selection for many traits and full recognition of the importance of the welfare of the birds.
Egg production has been improved consistently over 70 years and the industry continues to improve the efficiency of production by at least one per cent per year (Hy-Line and Industry data). This requires the simultaneous improvement of multiple traits including egg number, egg size, live ability, persistency and mature body weight. United States industry estimates are that egg number to 60 weeks ahs improved by more than one egg per year and Feed Conversion Ratio (FCR) is improving by 0.01 per year. A major component of this progress has been selection for improved robustness and disease resistance. Live ability to 60 weeks of age is 0.12% better each year and 0.18% better to 80 weeks of age. There is also continuing progress in uniformity of egg size and colour and freedom from defects. Again the most important feature of layer breeding programs is the ability to improve multiple traits simultaneously even though some of the traits will have adverse genetic correlations.
Although these rates of change cannot be entirely due to genetics, as discussed above, there are clear indications that the main driver for improved performance is genetics. However, many producers cannot or choose not to use the full genetic potential of the stock and set performance standards at locally acceptable levels.
IV. THE IMPORTANCE OF FEED CONVERSION RATIO (FCR)
The most important influence of genetics on the development of the poultry industry has been the improvement in FCR. Sustained improvements in FCR have an impact on the industry through the requirement for less feed per unit weight of products. This has affects on the demand for animal feed resources (mainly grains) and ultimately on the cost of production. There are also positive effects on the environmental impact of poultry production. Less water is required, less waste is produced and the environmental impact is reduced. All of these factors have an effect on the sustainability of the poultry industry. In discussing improvements in FCR it is essential to relate them to improvements in welfare. The objective of selection is to make the chickens fitter to perform well in a broad range of environments, production systems and disease challenges. These factors all contribute to overall bird welfare.
Comparing modern egg layers with those available 30 years ago shows that in 1975 it took 2.4 tonnes of feed to produce each tonne of eggs whereas today it takes 1.9 tonnes of feed to produce 1 tonne of eggs (Hy-Line and FAOSTATS). Today at least 115 Million tonnes of feed are used to produce eggs. Using the 1975 genotypes to produce all of todayís eggs would require 144 million tonnes of feed, an increase of 26 percent. The genetic improvements in efficiency are cumulative and permanent and this has made the products of the industry available to a higher proportion of the world’s population.
The improvements in broiler efficiency are even more dramatic. Between 1975 and today the combined effects of selection for growth, efficiency, yield and live ability have reduced the feed requirement for meat production from 20 million tonnes of feed per million tonnes of meat to 8.5 million tonnes of feed per million tonnes of meat (Aviagen and FAOSTATS).
The genetic potential of birds is even better but is not realized in all production environments. It took approximately 700 million tonnes of feed to produce the 81 million tonnes of poultry meat in 2005. Using a 1970s genotype would have required 1,600 million tonnes, an increase of 128%. The annual improvement of 2-3% in efficiency of meat production has made a huge cumulative impact on our ability to supply affordable animal protein to a growing proportion of the world’s population.
A recent study in Australia has examined the sustainability of animal production industries in light of the growing concern about the environmental impact of various production systems (Foran et al, 2005). By taking account of all inputs and outputs they compare the greenhouse gas emissions of beef, lamb and pork production with that of poultry meat and eggs. Beef production in Australia produces 26 kg of carbon dioxide equivalent per unit value. Poultry meat or eggs produce less than one tenth of this (2.5 kg carbon dioxide equivalent per unit value). Poultry meat and eggs also have 20% less impact than pork production (3.2 kg carbon dioxide equivalent per unit value) and 60% less than lamb production (6.4 kg carbon dioxide equivalent per unit value).
Thus the modern poultry industry has used genetic improvements in the birds that they care for to establish a very efficient and sustainable industry. Continued improvements in poultry should be faster than in other species because poultry breeders have advantages of population size, generation interval and genetic variation available to them.
V. THE FUTURE OF GENETICS IN COMMERCIAL POULTRY
Breeding companies have the responsibility to manage their genetic resources to deliver stock of predictable performance at high health standards. Population sizes must be sufficient to avoid inbreeding and ensure that the genetic variation is responsible to sustain long term selection responses. The most important developments in genetics over the last twenty years have been in the ability of breeding programs to deliver predictable and coordinated changes in multiple traits. Thus, selection for improved skeletal quality and heart and lung function has allowed simultaneous improvements in growth, feed efficiency and decreasing incidences of skeletal defects and ascites. Major investments are now being made to further improve the relevance and accuracy of the measurements made. This will allow more efficient and accurate selection to make progress in many traits.
Welfare traits. Successful breeding programs must recognize that they must place appropriate emphasis to the welfare of their pure lines and the crosses that will constitute their commercial products. In layers for instance this has required the application of group selection methodology to improve the live ability of layers when housed in populations. By reducing intra-group aggression, welfare and productivity have been improved together. In broilers and turkeys great emphasis is placed on improvements in skeletal quality, heart and lung function to improve welfare in the broad range of production environments. All successful breeding programs will ensure that welfare standards continue to improve to ensure that poultry production is a sustainable industry.
Robustness. Poultry production involves a broad range of environments which represent many different environmental, nutritional and disease challenges. Selection programs are now selecting to ensure that their products are robust and thus have predictable performance across this range of environments. The most important variable worldwide is disease challenge and breeding programs have incorporated selection for specific or general disease resistance. Production systems are changing in response to the needs of the birds or the preferences of public opinion, retailers and consumers. For instance, more layer birds are being housed in non-cage systems and breeding programs must ensure that birds will perform predictably in a range of alternative production systems. Nutritional variation has many components but the major divide in the world’s industry is between corn/soya diets and wheat-based diets. Wheat based diets offer a particular challenge for the predictable uptake of minerals for skeletal development. Besides selecting for birds that can perform in a broad range of environments the breeding companies will continue to cooperate with universities, research centres and producers to improve the advice given for the technical management of the stock.
Genomics. The publication of the chicken genome sequence (Hillier et al.2004) and a description of the variation between individuals (Wong et al. 2004) has quickly changed the structure and operation of commercial breeding programs. More than three million Single Nucleotide Polymorphisms (SNPs) are now available throughout the genome and the technology for large-scale genotyping is readily accessible. This means that associations can be established between marker SNPs and traits allowing more accurate selection for multiple traits. However, genomics is not an alternative to traditional selection methods but a means more fully describing the variation available within populations and of using the same phenotypic measurements to make more accurate selection decisions (Lamont and Dekkers,
2006). This will involve considerable investments in bioinformatics and an integration of traditional and new technologies. The benefits are likely to be greatest for traits that are difficult to measure (especially disease resistance and welfare traits) or traits of low heritability (e.g. some reproductive traits).
Ethics. Breeding companies have a major influence on food safety, animal health, animal welfare and the security of the food supply. They also have a responsibility to ensure that their programs are sustainable. This requires careful management and conservation of genetic resources. The number of products available continues to increase to meet many different production systems and environments and the demand for a wide range of products. Successful breeding companies must have a long term strategy for the management of their genetic resources for sustainable genetic progress in multiple traits over future decades. It is therefore important that they operate within an agreed ethical framework. Their products must be fit for purpose and support sustainable production. This requires that animal health and welfare are given full recognition by the selection strategies and that sufficient emphasis is given to traits affecting efficiency of resource utilization. The target is to deliver balanced, rapid genetic progress.
Breeding companies have worked with producers to revolutionize the production of poultry meat and eggs especially over the last fifty years. Genetic change continues and it is focused on the health and welfare of the animals as well as producer, retailer and consumer requirements. The investments required in research, development, production facilities and distribution systems means that there has been a decreasing number of breeding companies able to maintain a competitive position in the international market. Genetic change will continue to be a major contributor to the future development of the industry. The successful breeding companies will be those that make effective use of the feedback from producers, retailers and consumers in guiding their genetic programs. This will produce maximum benefits for food safety, animal health and welfare, efficient utilization of natural resources and will reduce the environmental impact of animal production.
ANDREESCU, C., AVENDANO, S., BROWN, S. R., HASSEN, A., LAMONT, S. J. And DEKKERS, J. C. M. (2007). Linkage disequilibrium in related breeding lines of chickens. Genetics 177: 2161-2169.
CRAWFORD, R. D. (1990). Poultry breeding and genetics. Elsevier, Amsterdam. FORAN, B., LENZEN, M. and DEY, C. (2005). Balancing act: A triple bottom line analysis of the 135 sectors of the Australian economy. CSIRO Technical Report, Sydney.
HAVENSTEIN, G. B., FERKET, P. R. and QURESHI, M. A. (2003a). Carcass composition and yield of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poultry Science 82: 1509-1518.
HAVENSTEIN, G. B., FERKET, P. R. and QURESHI, M. A. (2003b). Growth, livability, and feed conversion of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poultry Science 82: 1500-1508.
HILLIER, L. W., MILLER, W., BIRNEY, E., WARREN, W., HARDISON, R. C., PONTING, C. P., BORK, P., BURT, D. W., GROENEN, M. A. M., DELANY, M. E., DODGSON, J. B.,
CHINWALLA, A. T., CLIFTEN, P. F., CLIFTON, S. W., DELEHAUNTY, K. D., FRONICK, C.,
FULTON, R. S., GRAVES, T. A., KREMITZKI, C., LAYMAN, D., MAGRINI, V., MCPHERSON, J. D., MINER, T. L., MINX, P., NASH, W. E., NHAN, M. N., NELSON, J. O.,
ODDY, L. G., POHL, C. S., RANDALL-MAHER, J., SMITH, S. M., WALLIS, J. W., YANG,
S. P., ROMANOV, M. N., RONDELLI, C. M., PATON, B., SMITH, J., MORRICE, D.,
DANIELS, L., TEMPEST, H. G., ROBERTSON, L., MASABANDA, J. S., GRIFFIN, D. K., VIGNAL, A., FILLON, V., JACOBBSON, L., KERJE, S., ANDERSSON, L., CROOIJMANS, R.
P. M., AERTS, J., VAN DER POEL, J. J., ELLEGREN, H., CALDWELL, R. B., HUBBARD, S.
J., GRAFHAM, D. V., KIERZEK, A. M., MCLAREN, S. R., OVERTON, I. M., ARAKAWA,
H., BEATTIE, K. J., BEZZUBOV, Y., BOARDMAN, P. E., BONFIELD, J. K., CRONING, M.
D. R., DAVIES, R. M., FRANCIS, M. D., HUMPHRAY, S. J., SCOTT, C. E., TAYLOR, R. G.,
TICKLE, C., BROWN, W. R. A., ROGERS, J., BUERSTEDDE, J. M., WILSON, S.A.,
STUBBS, L., OVCHARENKO, I., GORDON, L., LUCAS, S., MILLER, M. M., INOKO, H.,
SHIINA, T., KAUFMAN, J., SALOMONSEN, J., SKJOEDT, K., WONG, G. K. S., WANG, J.,
LIU, B., WANG, J., YU, J., YANG, H. M., NEFEDOV, M., KORIABINE, M., DEJONG, P. J.,
GOODSTADT, L., WEBBER, C., DICKENS, N. J., LETUNIC, I., SUYAMA, M., TORRENTS,
D., VON MERING, C., et al. (2004). Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution. Nature 432: 695-716.
WONG, G. K. S., LIU, B., WANG, J., ZHANG, Y., YANG, X., ZHANG, Z. J., MENG, Q. S., ZHOU, J., LI, D. W., ZHANG, J. J., NI, P. X., LI, S. G., RAN, L. H., LI, H., ZHANG, J. G., LI, R. Q., LI, S. T., ZHENG, H. K., LIN, W., LI, G. Y., WANG, X. L., ZHAO, W. M., LI, J., YE, C., DAI, M. T., RUAN, J., ZHOU, Y., LI, Y. Z., HE, X. M., ZHANG, Y. Z., WANG, J.,
HUANG, X. G., TONG, W., CHEN, J., YE, J., CHEN, C., WEI, N., LI, G. Q., DONG, L.,
LAN, F. D., SUN, Y. Q., ZHANG, Z. P., YANG, Z., YU, Y. P., HUANG, Y. Q., HE, D. D.,
XI, Y., WEI, D., QI, Q. H., LI, W. J., SHI, J. P., WANG, M. H., XIE, F., WANG, J. J.,
ZHANG, X. W., WANG, P., ZHAO, Y. Q., LI, N., YANG, N., DONG, W., HU, S. N., ZENG,
C. Q., ZHENG, W. M., HAO, B. L., HILLIER, L. W., YANG, S. P., WARREN, W. C., WILSON, R. K., BRANDSTROM, M., ELLEGREN, H., CROOIJMANS, R., VAN DER POEL, J.
J., BOVENHUIS, H., GROENEN, M. A. M., OVCHARENKO, I., GORDON, L., STUBBS, L.,
LUCAS, S., GLAVINA, T., AERTS, A., KAISER, P., ROTHWELL, L., YOUNG, J. R.,
ROGERS, S., WALKER, B. A., VAN HATEREN, A., KAUFMAN, J., BUMSTEAD, N.,
LAMONT, S. J., ZHOU, H. J., HOCKING, P. M., MORRICE, D., DE KONING, D. J., LAW, A.,
BARTLEY, N., BURT, D. W., HUNT, H., CHENG, H. H., GUNNARSSON, U., WAHLBERG,
P., et al. (2004). A genetic variation map for chicken with 2.8 million single- nucleotide polymorphisms. Nature 432: 717-722.