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Introduction
The condition known as "cellulitis" was first assigned a condemnation code by Agriculture Canada in 1981. Since that time the condition has risen from an obscure condemnation category to the leading cause of condemnation in Canada from 1996-2006.
The E. coli bacterium is ubiquitous in the chicken's environment, its normal ecological niche being the intestinal tract. This organism's presence has been felt in the industry for many years, its involvement in conditions such as air sacculitis, omphalitis and yolk sac infections have had a substantial economic impact on the industry. With cellulitis, there is usually no indication prior to the flock going to slaughter of what losses will be incurred. We do acknowledge however, that the condition exists in almost every flock - it has become unusual to have flocks with no cellulitis lesions.
Emergence of Cellulitis as a Condemination Condition
In 1986, 0.048% of broilers slaughtered in Canada were condemned for cellulitis. In 1996 0.586% of broilers slaughtered were condemned for cellulitis. In 2004 that increased to 0.8% which means that approximately 4.7 million birds were lost to the marketplace due to cellulitis.
To understand how this condition, that was ranked number ten on the Canadian Condemnation list in 1986, has become a dominant factor in the broiler industry today, it is necessary to look at things that have changed in the poultry industry that were favorable to the development of this disease entity.
The E. coli bacterium
It would appear that the organism is basically the same today as it was in 1981 - a new "super bacterium" has not evolved. The general characteristics of E. coli have enabled it to be a successful organism in the past, present and likely the future.
The broiler chicken
Substantial changes have occurred in our broilers since 1981. We now have a chicken that can be grown to 1.8 - 2.0 kg market weight in less than 40 days! Much of this "improved" performance has come from genetics. This rapid growth has been implicated in leg and heart related problems that have resulted in increased mortality and condemnations. We also have feather sexable and high yield birds that tend to produce birds with less dense feather covering. The pressures that have been put on these birds to "perform" are an important factor in the emergence of the cellulitis problem.
Management practices
In this time period we have increased stocking density, decreased downtime, developed automated feeding systems and closed watering systems in environmentally controlled houses, implemented lighting programs, increased use of growth promotants, coccidiostats and vaccination programs. For the most part these changes have been aimed at improving the environment in which we raise broiler chickens. If everything is "perfect" you get a "perfect" flock! However, perfection in creating the ideal environment for growing today's broiler chicken is not easily achieved.
Predisposing Factors
We have created a system where we put a tremendous amount of pressure on the broiler chicken to grow rapidly - this has resulted in a great amount of physical and potentially immunologic stresses for the bird to handle.
Investigations into the predisposing factors that precipitate the development of cellulitis have resulted in a fairly lengthy list of conditions and management factors that appear to have positive correlation with the development of cellulitis. The development of cellulitis is multifactoral, controlling one of the predisposing factors may help reduce the incidence of, but it will not eliminate cellulitis.
The Bird
Feathering - poor feathering exposes the skin to physical damage and potentially E. coli. High Yield and feather sexable birds have slower or possibly even poorer feather development.
Growth Rate - today's broiler is programmed for rapid growth, this has been associated with an increased incidence of ascites and valgus leg deformities both of which appear to be positively correlated with a high incidence of cellulitis. These conditions may result in the bird spending more time sitting on the litter, thus, more exposure to E. coli.
Sex - the incidence in males is approximately twice that of females. Males have a faster growth rate, slower feather development and are more aggressive than females; all of which have been associated with high levels of cellulitis
Flightiness - nervous flocks tend to have more scratches. The development of Cellulitis appears to be secondary to physical damage to the skin. (However, the vast majority of birds have some scratches and not all birds develop cellulitis.)
(More research needs to be conducted into whether or not the strain of bird has an impact on the development of cellulitis.)
Management
Litter - a higher incidence of cellulitis is associated with straw litter. This may be because straw that is warm and moist will support bacterial growth better than wood shavings. All recycled litter has an increased incidence of cellulitis.
- wet litter is positively correlated with an increased incidence of cellulitis (however, high levels of cellulitis can also be seen in very dry barns.)
Downtime - the longer the time between clean out and restocking, the lower the incidence of cellulitis. The thoroughness of the clean out is also significant in reducing the incidence of cellulitis. The lower incidence of cellulitis observed with each of the above may simply be a result of decreasing bacterial numbers in the environment, thereby decreasing exposure to virulent E. coli.
Lighting Programs - in general lighting programs improve the overall health status of a flock, however, birds are more active therefore, the potential for more scratches exists. The potential benefits of improved leg strength and general health should not be overlooked when tackling the cellulitis problem.
Other diseases caused by E. coli - When the incidence of polyserositis is high, the incidence of cellulitis is increased. In addition to a high E. coli load in the environment, increased levels of polyserositis may indicate the presence of other important pathogens in the flock.
Temperature - Fluctuations in temperature in the brooding period may result in an increased incidence of cellulitis. It is not understood if this is related to feathering or to stress that results in a less thrifty bird.
- Warm temperatures in the grow out period may slow feather development thereby leaving areas of exposed skin late in the finishing period - a critical time for the development of cellulitis.
Growth promotants - these drugs tend to decrease gram positive bacteria in the gut and thereby may provide an opportunity for gram negative organisms like E. coli to multiply. The significance of this not understood and the benefits must be weighed against the potential negative effects.
Conclusion
From this list of "Predisposing Factors" we can develop a general list of ways to reduce the incidence of cellulitis.
1. Rear birds to promote feather development.
2. Reduce bacterial load.
3. Reduce growth rates.
4. Reduce other stressors - improve the overall health status of the flock.
It is not likely that we can eliminate cellulitis but, we can take steps to decrease its incidence. The changes that may have the greatest impact on cellulitis prevalence will mean rethinking current production strategies.
Just because we can grow a 2.0 kg broiler in 38 days doesn't mean we should!
References
Boulianne, Martine. Faculte de Medecine Veterinaire, St.Hyacinthe, Quebec. Personal communication.
Elfadil, A.A.;Vaillancourt, J.P.; Meek, A.H.;Julian,R.J.;Gyles, C.L.. Description of cellulitis lesions and associations between cellulitis and other categories of condemnation. Avian- dis. - American Association of Avian Pathologists Inc. July/Sept 1996. v. 40 (3) p. 690 - 698.
Elfadil, A.A.; Vaillancourt, J.P.; Meek,A.H.; Gyles, C.L.. A prospective study of cellulitis in broiler chickens in southern Ontario. Avian-dis. - American Association of Avian Pathologists Inc. July/Sept 1996. v.40 (3) p. 677 - 689.
Elfadil,A.A.;Vaillancourt, J.P.; Meek,A.H.. Farm management risk factors associated with cellulitis in broiler chickens in southern Ontario. Avian-dis. - American Association of Avian Pathologists Inc. July/Sept 1996. v. 40 (3) p. 699 - 706.
Goodhope, R.G.;Riddell,C.; Allan, B.J.. A descriptive study of cellulitis in Saskatchewan broiler chickens. Unpublished.
Kumor, L.W.; Olkowski, A.A.; Gomis, S.M.; Allan, B.J.. Cellulitis in broiler chickens: epidemiological trends, meat hygiene and human health concerns. Publishing pending.
Messier, S.; Boulianne, M.; Fredette, M.; Hameon, G.. La Cellulite Chez Le Poulet de Chair au Quebec. Colloque sur les Productions Avicoles
Sandra Stephens
Western College of Veterinary Medicine
University of Saskatchewan
Saskatoon, Saskatchewan
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