OCEAN CITY, Md. -- Consumer opinion and governmental legislation continues to limit or prohibit the use of antibiotics as growth promoters in food animal feeds in key areas of worldwide broiler production. These trends have created an industry demand in research to experimentally reproduce Necrotic enteritis (NE) outbreaks in broilers to evaluate present alternative control methods and potential future antibiotic replacements.
Four plus years of Clostridium perfringens challenge research at Colorado Quality Research (CQR) has identified alternative prevention programs that show promise for the future. We have also found variables or conditions that increase the incidence or severity of this pathogen's impact on broiler health and performance and managing these variables can assist the control of this disease.
An obvious, but frequently overlooked, disease risk factor is the pathogenicity and level of the actual Clostridium perfringens challenge. Some Clostridium perfringens isolates from actual commercial broiler outbreaks of NE are much more pathogenic than others and cause more severe lesions and mortality with the same challenge level and conditions. Some isolates tend to cause rapid and severe mortality with less impact on performance of surviving broilers while other bacteria isolates rarely cause mortality yet significantly decrease growth and feed conversion of infected birds.
Decreasing the bacterial load in the broiler environment especially in facilities with a history of NE outbreaks is primarily obtained by sound cleaning and disinfection of the environment between flocks. More attention to the efficacy of disinfectants and litter treatments against Clostridium sp. will become an important factor in controlling NE in the future.
The type and amount of coccidiosis present with the Clostridium perfringens is another key factor in causing severe NE with mortality or creating minimal effect on broiler performance with the bacterial challenge. It is very difficult to create NE or even performance impacting bacterial enteritis without some coccidiosis to provide an opportunity for the bacteria to infect the intestinal mucosal surface.
The severity of Eimeria acervulina and Eimeria maxima infections directly correlate with the ability to create enteritis and mortality in NE challenge research and it is clear that coccidiosis and Clostridium perfringens are the most frequent risk factors to consider when preventing field outbreaks. Thus controlling the bacteria and coccidiosis challenge and level present within broiler production facilities can greatly impact the risk of NE outbreaks or enteritis problems. Coccidiosis vaccines appear to be the industry direction of the future and managing the vaccine reaction of current vaccines or developing products that have minimal negative impact on the intestinal mucosa surface will also decrease the risk of secondary NE outbreaks.
Chick quality and uniformity is another variable that research has determined to impact the ability to create enteritis and NE mortality. It is much easier to reproduce NE mortality and impact broiler performance when challenging chicks that have experienced bacterial challenge such as omphalitis and flock uniformity has suffered. The smallest birds in such flocks are consistently the first birds to succumb to the Clostridium perfringens challenge. Very healthy and uniform flocks of chicks are consistently difficult to cause and reproduce NE lesions and mortality when conducting challenge research. Flocks with excellent chick quality and uniformity take a greater challenge to create disease, so continued improvements in consistent chick quality should improve the control of necrotic enteritis. Avoiding placing known inferior quality or stressed chicks into facilities with a history of NE outbreaks should assist the prevention and severity of these outbreaks.
Our research also indicates that the chick source can impact the severity of Clostridium perfringens challenge necessary to create disease. It has been obvious that some chicks simply take less challenge to succumb to enteritis than others. Do some chicks simply have a different initial bacterial microflora that helps protect them from the enteritis challenge or is this breed or breeder flock related? Specific studies have suggested a difference between breeds in their ability to overcome the enteritis challenge and the difference was at least breeder flock source related.
This difference found in chick sources could also be associated with differences in maternal antibody against Clostridium perfringens. This opens the opportunity of vaccination of breeders and/or broilers to assist in the future control of this pathogen and/or the development of breed lines that are more resistant to the disease. Data has been presented from a recent study evaluating a new toxoid vaccine for breeders to provide maternal antibody to progeny to protect against necrotic enteritis. The study showed that the maternal antibody from the toxoid vaccine was efficacious in broilers on a coccidiosis vaccination or ionophore program.
Our research has found that ionophore coccidiostats are also very effective in protecting against a necrotic enteritis challenge. In fact birds receiving an ionophore consistently perform better than the non-challenged controls. Ionophores have antibacterial properties and this assists the control of NE compared to chemical and vaccine anticoccidial programs.
Additional vaccine candidates that are administered directly to the broilers have been tested and some appear to have potential. Finding a vaccine that can be administered in ovo or sprayed as a live vaccine would have the greatest potential for commercial success.
Intestinal microflora management has shown excellent benefits in preventing NE in our research model. Providing live bacteria that are good for the intestine (Bacillus, Lactobacillus, etc.) has shown to help protect against necrotic enteritis. We have also found that products that have antibacterial properties that are not damaging to the "good" bacteria can be protective against Clostridium perfringens even if the product has no direct effect against Clostridium sp.
Nutritional risk factors have also been found to be associated with increased NE mortality and enteritis in challenge studies. Broilers receiving high protein diets are simply easier to successfully challenge with Clostridium perfringens. The higher the protein level directly correlates with the level of disease created in our research. Over feeding of protein appears to increase the risk of enteritis disease conditions and feeding broilers lower density diets decreases the ability to create enteritis. This association may be due to nutrients remaining available to the bacteria in the intestine if they are being fed at higher levels than the broilers can utilize efficiently. This suggests that integrators attempting to raise broilers without feed grade antibiotics may be able to decrease the incidence of NE by using lower density formulations or concentrating on amino acid fortification and balance rather than feeding diets with higher protein levels.
The ingredient source and quality of high protein ingredients can also greatly impact the severity of bacterial challenge necessary to create enteritis. Diets with high levels of animal by-products (fishmeal, meat and bone meal etc.), and especially animal by-products highly contaminated with Clostridium sp. spores, assist researchers to reproduce NE mortality and enteritis conditions. Clostridium perfringens enteritis and mortality has been reported in chicks as early as 2 to 3 days-of-age when fed a high protein ration that contained fishmeal that was highly contaminated with Clostridium sp. spores. Monitoring of ingredients for Clostridium sp. spores and avoiding these ingredients when possible is a current and future practice that will decrease the risk of NE outbreaks.
Research has also found that rations with high levels of wheat, rye or barley also assist reproducing severe enteritis and NE mortality. The quality of these ingredients could also play a role in increasing or decreasing the risk of enteritis outbreaks in research studies and commercial production. It has also been clear that dramatic changes in the level of some of these ingredients during the broiler growout (starter versus grower feed, etc.) greatly increases the risk of an NE outbreak. Avoiding dramatic changes in the diets of the birds will improve the control of this disease. The broiler nutrition program must also be considered when discussing the management risk factors associated with NE mortality and enteritis associated performance problems.
Management risk factors associated with enteritis are generally associated with effects on feed consumption, litter conditions and timing of these risk factors. Necrotic enteritis challenge studies have shown that high feed consumption rather than feed restriction (light restriction, etc.) increase the risk of an outbreak. Studies have found that chilling broilers (which increases the feed consumption) compared to heat stress (decreases feed consumption) assists developing NE mortality and conditions that encourage a high consumption of higher density feed is an even better environment for causing an NE outbreak. It appears that increasing the environmental temperature and light restriction to decrease the feed intake of a broiler flock breaking with NE will help curtail the severity of the outbreak.
The NE research has also found litter conditions and possibly the type of litter can increase or decrease the disease risk. Higher litter moisture obviously increases the incidence and severity of NE and is most likely associated with increased coccidiosis challenge and cause a chilling effect on the broilers. Oat or rice hull litter may also increase the risk of enteritis due to being less absorptive of moisture as well as increased consumption by the broilers which would increase the consumption of coccidia oocysts and bacteria. Litter type and treatment products have become a valuable tool in assisting the control of NE and continued research in this area will be valuable to the industry in the future.
The timing of all of the risk factors listed above must be considered while managing enteritis because it appears that broilers are at the greatest risk between two and three and a half weeks-of-age. Avoiding these risk factors during this time of the broiler growout will decrease the incidence and severity of necrotic enteritis. Management to minimize the number of these risk factors impacting a broiler flock simultaneously will greatly decrease the risk of an enteritis outbreak.
Dr. Steve Davis is president and CEO of Colorado Quality Research Inc. in Wellington, Colo. This article is drawn from Davis' presentation at the 2006 National Meeting on Poultry Health and Processing in Ocean City, Md., Oct. 9-11.
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