Broiler production of the future - The shape of things to come from biosecurity to pollution control

It is always an interesting challenge to predict the future direction of any segment of animal agriculture.

Predictions are often based on personal intuition, rather than conventional referreed journal sources that are the common basis to most papers at this meeting. Such freedom of thought is quite stimulating, although I realize that many other participants will have differing views. Certainly there is a wealth of generally non-technical literature discussing future directions of the poultry industry, and to some extent one can select data to accommodate almost any view. In retrospect I’m sure this paper will be viewed in much the same context in future years. I have taken the position of referencing relatively little in the way of corroborative prediction analyses, rather the context of this paper is my own personal view based on some 25 years experience of working with and visiting all segments of the poultry meat industry. I have been fortunate in visiting poultry operations in many different countries, and have come to realize that while certain geographical differences exist, the general thrust of broiler production systems is very standardized. Regardless of all current challenges, the growth rate of the modern broiler chicken has evolved dramatically over the last 30 years (Figure 1) and there is little indication that this trend will change within the next five years or so. The reader is directed to Nunes (1997), Roenigk (1999) and Phipps (2000) for some general background reading on trends in production and current issues facing poultry meat production.


World statistics

Although some variation exists in current and predicted production and consumption data, one statistic is undeniable - namely that in all countries over the last 20 years, there has been a continued increase in poultry meat consumption. As yet, I have never seen a statistic that shows a decline, however small, for consumption of poultry meat on a yearto- year basis. In most countries this increase in consumption has occurred due to either a) poultry replacing beef as a consumer choice in meat products and/or b) there being an increase in per capita consumption of meat in general. In 2010 there is a prediction for consumption of around 55m tonnes of broiler meat, which equates to a yearly live production of 74 m tonnes or about 37 billion 2 kg birds. The industry will require some 145 m tonnes of feed at a value of close to $30 billion.

Figure 1. Changes in body weights of broilers from 1972 to 2002.

These statistics assume a more moderate annual growth than has occurred over the last 20 years (about 1 million tonnes live bird annual increase), but still the numbers are quite impressive.

There will likely be a subtle change in where this future production occurs. Currently we have major production centers in the Americas, Europe and Asia. The Americas and Asia will continue to meet world demand, while Europe seems destined to supply its own local market for niche products.

Within the Americas, the USA and Brazil will continue to be the major producers and exporters while in Asia, China and to a lesser extent Thailand will be the most important sites of production. It is obvious that while it is possible to produce broilers in almost any geographical region, it is the location of ever more sophisticated processing facilities that dictate major centers of production. Some countries will continue with marketing of live birds (e.g. Mexico and Peru) and while this effectively excludes imports, it does limit future expansion and profitability. Processing and further processing are the keys to market penetration of poultry meat, and these facilities are becoming increasingly expensive to establish and maintain. The current trend toward producing heavier birds is merely a response to reducing processing costs per unit of meat yield.

However there are current limits to how heavy we can economically grow birds, and without the interaction of genetic engineering, we are likely close to the upper limit in live broiler weight. The limiting factor to processing in the next 20 years will be an adequate and economical supply of water that meets ever increasing standards for pollutants and contaminants. We will meet these standards by utilizing water purification systems, which will necessarily add to our cost of production.

The only real challenge to the dominance of global poultry meat production will come from the swine industry. As they develop production strategies similar to those reminiscent of broiler chicken production, such specialization and economy of scale will result in a cheaper cost of production. However their higher maintenance energy requirement will always mean a less efficient feed utilization; and so the broiler industry will continue to be leaders in least cost producers of lean meat. Also, as the pork industry delves into further processing, like the poultry industry, they will see advantages to marketing of heavier pigs, and this will help the broiler industry to maintain its competitive edge. It seems likely that the emerging modern swine industry will mirror developments in the poultry industry, and in most situations our main competitor will be physically situated in very close proximity to poultry producers.

However, it seems as though our customer base is changing quite dramatically. In North America at least, less than 50% of consumer food purchases are at conventional food stores. About one third of such spending now occurs in restaurants of all descriptions, and 20% at other food service outlets such as schools, hospitals, prisons and various entertainment venues. Either our current broiler integrators will have to accommodate this changing clientele, or a new level of entrepreneur will emerge, as middle-men who will manufacture such products as HRM (home replacement meals) where chicken is but one item in the saleable product. While the poultry meat industry has always led in innovative processing and new product development, the next 10 years will see an even greater emphasis in this segment of the industry.


Genetic selection

It seems unlikely that there will be any major change in emphasis for genetic selection in the near future.

Over the past 20 years, we have seen a 25-50 g per year increase in weight of broilers at 42-49 days of age and this trend will continue in the foreseeable future. There is an obvious limit to this growth potential that is fueled by the bird’s voracious appetite, the most likely reason being problems with the bird’s skeletal and cardiovascular systems.

The heritability for growth characteristics is quite high, being in the order of 0.4-0.6 (or 40-60%). This means that fairly rapid progress can be made by simply selecting as breeders the heaviest birds in a flock. There is a common misconception that a heritability of 0.5, for growth rate for example, means that we can increase the growth potential of a bird by 0.5 (50%) each generation. In reality, the response to selection for each generation is defined as H² x selection differential. The selection differential is the difference between the selected individuals and the average of the flock. For example some male birds are selected because they are 200 g heavier than the flock average. Heritability for growth is 0.5, and so selection response will be 100 g. Due to genetic selection, the next generation can be expected to be 100 g heavier than the mean of the two parent lines. The male only provides 50% of the genetic material to his offspring, and so this effect is further diluted by the lower selection pressure that can be applied on the female line. The bottom line is that the 25-50 g increase each year in weight-for-age that we have seen in our broilers over the last 15-20 years is rather a remarkable achievement by the primary breeders. This situation is even more impressive when consideration is also being given to so many different traits in a breeding program.

For this trend to be maintained over future generations, the primary breeders must continually find individuals within their pedigree lines that are 100-200 g heavier than average. Anyone who handles and weighs individual birds knows that such individuals exist, yet finding enough ‘fit’ individuals each generation becomes increasingly difficult.

Currently in small experimental male flocks, averaging 2.7 kg at 42 days, we see individuals weighing 3.2 or even 3.5 kg, and so variation still exists. In fact, at our research facilities we are becoming more concerned with bird-to-bird variation, which seems to be increasing, and is making the identification of various treatment effects more difficult. This variation is present at 7 days of age, and is becoming more obvious over time.

Carcass meat yield, especially breast meat, has become a major factor in selection of male line breeder candidates. The emphasis on breast yield has been fueled by the premium realized for this meat in North America, a situation that often does not occur in other countries. Anyone fortunate enough to visit a primary breeder and see and handle male line breeder candidates at the GGP or pureline level, knows that the future will see broilers that resemble current strains of small turkeys in terms of breast development.

Another trait often considered is feed efficiency.

Feed efficiency has improved gradually over the last 20 years and will continue to improve in the future. This improvement is not a consequence of improved digestibility, since for most ingredients this has been around 90% for the last 50 years or so.

The improved utilization of feed is merely a consequence of reduced maintenance need because of an earlier marketing age for a fixed weight category. There has perhaps been some improvement due to a leaner carcass since muscle contains 80% water, yet this factor is also influenced by diet energy level.

In considering genetic programs for broilers, one cannot ignore the need for efficient breeder production. However, the economics within an integrated operation are such that broiler characteristics far outweigh breeder traits. Carte (1986) eloquently detailed this comparison for broiler vs breeder traits within a genetic selection program (Table 1). These data have been modified to reflect economics more realistic in 2002.

These data suggest that, all other factors remaining the same, a +0.18 kg increase in live weight at a specific market age will reduce overall costs by 1¢/ kg broiler live weight produced. Increasing breast yield by 0.9% has the same economic benefit, etc.

Of particular interest are the relatively large changes that must occur at the breeder level in order to bring about the same economic return. For example, obtaining an extra 30 hatching eggs from every breeder is equivalent (economically) to reducing feed efficiency in their offspring by 0.06 units. An alternative way of expressing this comparison is to suggest that an integrated operation could give up 30 hatching eggs per breeder if the result was -0.06 units improvement in feed efficiency of commercial broilers. Over the next 10 years or so, the industry cannot expect any major change in breeder performance.


Production systems

Over the past 15 years there has been substantial consolidation in the type of housing and construction systems of broiler facilities used worldwide. Anyone building new facilities today will likely design sites for 8-10 houses, each holding around 50-60,000 birds.

These houses will be controlled environment (blackout) or open-sided with more elaborate insulated curtains, incorporating tunnel ventilation. While simple pole and wire structures were commonly built in temperate regions in the 1970s, we now realize that the extra cost involved in having greater control over environmental conditions is more profitable over the 20-25 year life span of the building. I do not think that we will see any major future change in the size or construction type of broiler houses.

With additional help during catching and clean out, mechanized systems allow for one person to manage at least 100,000 birds, and so this becomes the approximate minimal economic size for newer construction. We will not likely see any further reduction in labor input, assuming that we wish to practice good husbandry and have our birds inspected on a regular basis. With broilers being marketed at heavier weights, cage systems seem destined to oblivion. There has been discussion about the concept of a central cage brooding facility, flanked by conventional floor growout houses, much as occurs in some areas with specialized turkey brooding units. However the extra labor, and potential insults involved in physically moving broilers at 14-17 days of age, however short a distance, will undoubtedly relegate such systems to ‘demonstration’ units.

Locating new farms for any expansion operation is becoming more difficult. Some 30 years ago, producers in tropical climates were encouraged to abandon their low-lying farms and establish new facilities at higher altitudes, which were much cooler. This effectively resolved the then major problem of heat distress. Since this time, we have seen the emergence of ascites as a major cause of mortality, where keeping broilers of any age at <15ºC seems to trigger major problems. Unfortunately, there are always cool/cold nightime conditions at high altitude and so these new locations are now unsatisfactory. So, once again we are concentrating on lower altitude sites for broiler farms, since today, the effects of heat distress can be better managed with new environmental systems. Finding such sites is becoming more difficult, because we usually want to be within 100 miles or so of the processing facilities and feed mill, and ideally for reasons of biosecurity, 2-3 km distance from any other poultry farm.

Another future consideration is an adequate supply of ‘clean’ water for any broiler operation. In many regions, ground water levels are getting lower, which means more power is required to pump to surface levels. In arable regions, the levels of minerals and pesticides will become more critical as a consequence of their gradual (20-30 year) movement through soil, and our inevitable advances in being able to detect ever-decreasing quantities of residues (ppt) of virtually any compound.


Nutrition and feeding

Feed will always be the major input cost for broiler meat production. Corn and soybean meal will remain the basis of all broiler diets, and for this reason North America and Brazil will continue their dominance in production. There are really no major alternatives to corn and soybean meal on a worldwide basis. In certain regions, wheat is used because of artificial price support and/or artificial import tariffs on alternatives, and rice bran will continue to provide a niche role for diets in Asian countries. One often hears about ‘new’ alternate feed sources and byproducts.

Such discussion shows lack of understanding of world animal production, and whereas a few hundred tonnes of a ‘new’ byproduct can be fitted into some local production system, there simply is not any undiscovered ingredient that is going to have an impact on the price of corn and soybean meal.

To a large extent, broiler production, and world food supply in general, is at the mercy of weather patterns in Brazil and the midwestern USA. For the last 10 years at least, the world has had an abundance of cheap grains and vegetable proteins, and the broiler industry has capitalized on this situation. However, long-gone are the 3-5 year grain reserves held in silos throughout North America.

We are now very much using a just-in-time supply of raw ingredients from seasonal supplies north and south of the equator. Just one year’s disastrous crop yields in North America or Brazil will have an unprecedented impact on feed supply, and probably will be the impetus that makes consumers appreciate the current value of all meat and animal products. With greater changes in weather patterns, a disastrous growing season is inevitable at some time in the future.

While corn and soybean meal will continue to be the main constituents of broiler feeds, the role of meat and poultry by-product meals and animal fats is less predictable. Meat meals provide a useful source of digestible amino acids and an important source of phosphorus. If they are banned from use in broiler diets, feed costs will increase by about 5- 7%. Currently the animal feed industry provides the ultimate route for re-cycling of these wastes. If they are banned, then society will be faced with an unprecedented task of finding alternate disposal.

If one is truly serious about the role of prions in the food chain, then using processing wastes as a fertilizer cannot be considered, because grazing animals and predators will conceivably continue their cycling through animals. The only scientific solution is to incinerate such waste, which will impose an unprecedented increase in the cost of animal production. It may well be that an initial step will be banning of feeding by-products from a particular species back to that species, much as the current ruminant-ruminant ban now in effect in many countries. The use of rendered animal products in poultry feeds will likely be a basis for import control of broiler meat.

The use of genetically modified cereals and vegetable proteins is another contentious issue. The general area of biotechnology and genetic engineering is still in its infancy, and will undoubtedly have a major impact on most aspects of agriculture and human medicine. It is unfortunate that the first commercial examples of this technology were seen to benefit only certain segments of society. Changing the nutrient profile of ingredients is not going to have a major effect on feeding broilers since if the bird’s requirements do not change, then the net overall effect will be zero. For example, using a high lysine corn means that we will need less soybean meal or synthetic lysine.

Modifying the nutrient level of plants will merely represent a net shift in the source of individual nutrients, assuming these are cost effective substitutes. More exciting is the potential to reduce the levels of antinutrients. Limiting or eliminating the levels of trypsin inhibitor in soybeans for example, would have a major effect on monogastric nutrition. Likewise eliminating phytic acid and/or replacing this with a soluble storage phosphate in the plant would be welcomed by nutritionists and environmentalists. Eliminating the levels of these ‘toxins’ may also be more acceptable examples of GMOs for the consumer. A major challenge facing the feed and broiler industries in using these new ingredients will be to maintain product identity from the arable field to diet manufacture at the feed mill. Currently soybean meal, as an example, is a single commodity and mill managers are going to be less than enthusiastic when confronted with perhaps four or six ‘varieties’ bioengineered for various reasons. Bin space is usually a limiting factor at most mills, since these take up proportionally the most space in the physical mill structure.

Some type of HACCP program will become mandatory at feed mills and this will extend from concern over residue of pharmaceutical products through to microbial control. Undoubtedly the microbial status of animal products in general is going to be the single largest factor influencing the success of future production systems. Feed is but one source of such potential contamination, and contrary to popular belief, elimination of meat meal from the formulation is no guarantee of producing feed devoid of microbes pathogenic to birds or humans.

It seems obvious that our grains and vegetable proteins are subject to microbial contamination prior to, or in storage at, the feed mills. Few important microbes can withstand feed treatment at 80ºC, hence the trend to higher pelleting temperatures.

However recontamination following pelleting is still a major problem; and the use of organic acid/ formaldehyde treatments etc. may become more popular to maintain ‘clean’ feed delivered to the broiler’s feed trough. The issue of in-feed antibiotics and/or alternatives is dealt with in the section on health management.


Health management and microbial status of broilers

Considering the scale of production of modern broiler farms, birds are remarkably healthy and well over 90% of chicks placed realize their genetic potential.

Average mortality is around 5-7% for males and 3- 5% for females, depending upon age of marketing.

It is doubtful if any other land-based farming operation could manage so successfully such large numbers of animals within confinement facilities.

Our current success is due to genetic selection, availability of efficacious vaccines and antibiotics and a growing awareness of the importance of biosecurity and general farm hygiene.

Today, infectious disease is not usually the major cause of mortality or morbidity, even though such infectious agents are ever present on the farm or in the general locale. Our major concerns are more often loosely termed ‘metabolic disorders’, the most notable ones in order of economic importance being Sudden Death Syndrome, skeletal disorders and ascites. Of these conditions, ascites has received considerable attention, and the etiology is fairly well established. The trigger to the condition is fast growth rate aggravated by cool temperatures (<15ºC), which increases the bird’s oxygen demand.

Worldwide, however, the most important condition is still Sudden Death Syndrome, the etiology of which is far from clear. Most metabolic derangement can be prevented by growing birds more slowly, a situation that is often not economical.

For example, it may not be economical to slow down the growth rate of 100% of a flock, merely to ‘treat’ 3% of the birds that may become afflicted. If growth control is considered, then systems that affect early development must be considered.

Figure 2 shows the trend in male broiler growth over the last 30 years with broiler growth expressed as percentage weekly gain. The most striking feature is growth potential in the first week, where today we have a male broiler capable of increasing its body weight by 300%. Using specialized prestarter diets, we have actually achieved a 400% increase in the 0-7 day growth, yet the 300% achieved with commercial diets is quite extraordinary compared to other farm animals. Relative growth after this time is little different, yet the additional weight achieved by day 7 is compounded by subsequent weekly percentage increases, such that by 8 weeks we have a broiler that today is 1 kg heavier than its 1970 counterpart. However, tempering this early growth, for reasons not fully understood, does seem to reduce the incidence of metabolic disorders occurring after 28 days of age.

Such growth reduction can be achieved by using mash diets, diets of very low nutrient density, perhaps by physical feed restriction, or more commonly by extended periods of darkness. We can temper early growth rate without too much loss in feed utilization, since during the first week of growth some 80% of feed is used for growth and only 20% used for maintenance. At 49 days of age only 20% of feed is used for growth while 80% is used for maintenance; and so trying to temper growth at this age is detrimental to feed efficiency.

If mortality/morbidity can be reduced enough by a system of early feed ‘restriction’, then the overall feed efficiency of the flock can actually be increased. There is some indication of compensatory growth in broilers (Zubair and Leeson, 1996).

Unfortunately, I do not think that we will be able to sustain such ‘corrective management procedures’ to what is effectively a consequence of genetic selection for faster growth and an ever increasing potential for nutrient consumption. In the near term (5-15 years) I think that current and emerging metabolic disorders will be of sufficient magnitude to necessitate a moderation in selection pressure for growth rate.

The general lack of problems caused by viral infections is due the availability of easily administered vaccines. The life cycle and make-up of the virus makes it less likely or able to mutate than do bacteria, and so commercial vaccines have relatively long lifespans. Obviously new strains or variants emerge, and this will continue in the future.

Figure 2. Percentage weekly increase in growth of male broilers.

Of more concern is endogenous viral DNA as recently seen with ‘J-virus’ leucosis. The avian leucosis virus contains a protein core whose composition is controlled by a specific gene group.

This gene (group specific antigen) is used in sophisticated laboratory diagnosis. This protein core is itself encapsulated with another protein coating, the development of which is again controlled by another gene group within the bird. Unfortunately the viron core can replicate and integrate itself with the bird’s own DNA sequencing. The endogenous virus can therefore replicate itself, and the bird can shed the virus. However because the viral protein is part of the bird’s own DNA, it is not recognized as ‘foreign’ and so there is no antibody produced.

While the current ‘J-virus’ has been virtually eliminated by costly screening of pureline genetic stock, the potential emergence of comparable ‘K’ or ‘L’ viruses at some time in the future will test the vigilance of breeding companies.

Control over coccidiosis and necrotic enteritis is likely to be our major future concern regarding infectious disease. With the introduction of ionophore anticoccidials concerns over coccidial control diminished, since products such as monensin were universally efficacious. Resistance to older chemical coccidiostats occurred quickly, since their mode of action involved only a few enzyme systems within the oocyst controlled by a limited number of genes.

The ionophores on the other hand caused massive disruption to cell membranes, affecting virtually all enzyme systems and control mechanisms. As anticipated, it has taken oocysts much longer to mutate such that they can withstand this more widespread disruption to their various systems.
However there is little doubt that this is occurring.

Unfortunately, ineffective control of coccidiosis often leads to necrotic enteritis caused by an opportunistic clostridial bacterium. While coccidial vaccines have been used successfully for breeders, their use to date for broilers has met with limited success, again due to development of resistance. A novel approach in the future may well be the sequential use of a vaccine followed by an ionophore anticoccidial (Lee, 2001). In the past, vaccines and ionophores have been considered to be mutually exclusive, although the intriguing concept outlined by Lee (2001) may prove this to be a myth, and in fact, there is great logic in considering them in a shuttle program within a given flock.

Biosecurity is an integral part of health management, and if pathogens can be kept out of the facilities, bird health must benefit. Various degrees of biosecurity exist throughout the world, with the highest standards being seen in Central and South America, and the worst (often nonexistent) in North America. To some extent the current levels of biosecurity are a reflection of endemic disease challenge. In the future, biosecurity must improve, especially since we will likely place less emphasis in routine use of in-feed antibiotics.

Various levels of biosecurity exist, and these have corresponding effects on day-to-day cost of production. It is sometimes difficult to warrant such costs, since the alternatives (disease challenge) are difficult to predict. Table 2 outlines various levels of biosecurity that can be considered for broiler (and breeder) facilities. In the future, we will undoubtedly move to medium or high levels of biosecurity at both
breeder and broiler complexes.

Current production systems rely on feed-borne antibiotics and growth promoters. With current growth rates of broiler chickens the classical effects of growth promoters are less easy to quantitate.

However most of these compounds are efficacious against clostridial infection and without them, it is impossible to always control necrotic enteritis and associated outbreaks of coccidiosis. However, it seems as though we are destined to routinely use less of these pharmaceutical products, and while they may be available on prescription for treatment use, alternatives are a fruitful area of research and development. So-called probiotics and prebiotics seem logical alternatives to antibiotics and growth promoters, and the key to their use is very early dosing of the bird. I think that treatment of chicks on arrival at the farm will, in fact, be too late to prevent colonization of pathogens. This leaves the hatchery as the most logical site for treatment. It is conceivable that treating chicks in their delivery boxes, much as happens with spray vaccines, may also be too late for beneficial live bacteria to become established in the gut. In the future, I think we will see treatment in the hatchers or even at 18 days of incubation with incorporation into the Marek’s vaccine.

Re-use of litter material is another contentious issue. In the USA, 6-8 flocks are commonly grown on the same ‘built-up’ litter, while in most other regions of the world litter is removed and houses thoroughly cleaned after each crop of birds. Many producers argue that re-using litter simply does not fit into modern biosecurity and health management programs. However, if the previous crop of broilers was ‘healthy’, then their litter and the ‘dirty facilities’ provide a useful resource for initiating a competitive exclusion program, i.e. the general microbial population from the previous flock is used to seed the next flock of birds. Rather than dismiss the idea of reusing litter, I think that there are certain circumstances where it can be used to advantage in a health management program.


Environmental issues

Until quite recently the broiler industry has been generally unaffected by the environmental issues that have arisen with some other intensive animal industries. Broiler manure (litter) is relatively easy to handle and does not have the same odor problems usually associated with intensive swine farms and beef feedlot operations. However the sophistication and scale of poultry processing facilities today means that broiler farms are necessarily located within reasonable trucking distance of this central unit. This intensification of bird numbers inevitably leads to greater challenges for proper disposal of manure. The current and future problems are somewhat predictable based on the past experiences seen by the animal industries in Holland and Taiwan.

We can certainly reduce nitrogen (N) and phosphorus (P) output in manure, simply by limiting the dietary inputs. In many situations today it is still most economical to over-formulate for these two nutrients and imposing maximum constraints during formulation leads to increased cost. The impetus to reduce N and P loading of manure will necessarily come from legislation involving nutrient management of farmland. In these situations, P is likely to be the major problem, since in many areas today we are at the saturation point in soil levels of P as dictated by current environmental guidelines. Corn and soybean meal take minimal quantities of P from the soil, suggesting that conventional cropping is not a short-term solution to any future problems. The P levels in soil can most quickly be depleted by growing forages and removing this as hay or silage, a situation that is not always convenient in areas of intensive poultry production.

We can certainly reduce the P output of broilers through use of phytase enzyme added to feed, although it is unfortunate that conventional pelleting temperatures deactivate most sources of phytase.

Low-phytase content corn and soybean meal will certainly help to limit P excretion. Incineration may be an answer in many locations.
With efficient incineration, only inorganic elements remain, and these can be used as a fertilizer and/or as an animal feed ingredient. The ash remaining after incineration is much condensed in volume (95%), and can be more economically moved away from the immediate area of production, possibly to locations where the corn and soybean used to feed the birds was grown. Intensive broiler production does not ‘create’ P or N, it merely concentrates their presence, and redistribution back to the original source seems the ultimate example of recycling.


Conclusions

There will not be any decline in broiler meat production over the next 20 years. Corn and soybean meal will continue to be the basis of diets worldwide, although new ‘strains’ of plants may lead to alternate routes for sourcing nutrients. Genetic engineering of plants can have the greatest net impact on the broiler industry by eliminating or reducing the content of antinutrients.

Metabolic disorders will continue to be a major‘health’ issue, although the biggest unknown factor relates to our ability to control coccidiosis and necrotic enteritis. We will likely need to maintain bird health with less routine reliance on antibiotics; and so the study of intestinal microbiology will be critical to future production strategies. Biosecurity will also become a critical feature of any health management strategy.

Environmental issues and particularly the handling of phosphorus will have to be addressed in areas of intense production. Currently, incineration of litter holds most promise, since the residual ash can more easily be redistributed to areas of lower soil phosphorus, meaning that broiler manure can once again be considered an asset rather than a liability.


References and Suggested Reading

Carte, I.F. 1986. Genetic economics of chicken meat production In: Proc. 3rd Wld. Cong. Genetics Appl. Livestock Prod. Vol. 10:228-235.

Lee, E.H. 2001. Method of protecting against chronic infection. U.S. Patent #6, 306, 387.

Nunes, K. 1997. Retooling retail. Meat and Poultry. April. P. 19-28.

Phipps, R.H. 2000. GM Crops: An alternative view to Greenpeace. Feed Compounder June/July p. 44-47.

Roenigk, W.P. 1999. World Poultry Consumption. Poultry Sci. 78:722-728.

Zubair, A.K. and S. Leeson. 1996. Compensatory growth in the broiler chicken: A review. Wld. Poultry Sci. J. 52:189-201.