Management, epidemiology, and economic impact of enteric bacterial diseases in broilers

Dr. Charles L. Hofacre, president of the Southern Poultry Research Group and professor emeritus at the University of Georgia, was in charge of the presentation on “Management, epidemiology, and economic impact of enteric bacterial diseases in broilers” at LPN 2018.

Poultry nutritionists, veterinarians, and animal scientist specialists face numerous changing regulations, consumer preferences, and the ongoing responsibility of rearing healthy birds in a profitable way.

These regulations include changes to the use of antibiotics, increased food safety, and concerns about how birds are raised and how house waste is managed.

In the context of the evolution of this business environment, the prevention and control of enteric diseases have become one of the main priorities of the broiler industry.

Enteric bacteria strongly impact bird performance, health, welfare, and food safety.

Two primary enteric bacterial diseases that pose a challenge for broiler production today, which will be addressed in this paper, are Necrotic Enteritis and Salmonella.

Necrotic Enteritis

The withdrawal of growth-promoting antibiotics and ionophore anticoccidials from poultry feed, either due to new regulations or new market trends, has led to a higher frequency of severe cases of necrotic enteritis. It is estimated that the cost associated with subclinical necrotic enteritis (impairs the digestion and absorption of nutrients) could amount to 5 cents per bird.

Based on estimates and those of global broiler meat production, the cost of this enteric disease to the poultry industry could be nearly $2 billion U.S.D.

Necrotic Enteritis (NE) is caused by Clostridium perfringens (CP) type A, which produces alpha and beta toxins. CP forms spores that are very resistant to environmental changes, being able to persist for long periods. CP is an anaerobic gram-positive bacterium found in soil, dust, feces, feed, and especially in the litter of chickens and turkeys.

Necrotic Enteritis can appear in 3 ways:

• Hyperacute
• Acute
• Subclinical

It manifests mainly in broilers from 10 to 28 days of life. Clinical signs include depression, huddling, ruffled feathers, lack of appetite, diarrhea, and, in severe cases, high mortality.

This enteric disease beginning can occur rapidly, and mortality can range from 2% to 50%. The subclinical form does not cause mortality but reduces feed efficiency. The disease could manifest as hepatitis or cholangiohepatitis in chickens at processing age.

The lesions vary from mild cases that could be confused with coccidiosis, dysbacteriosis, or viral enteritis. The primary lesions include enlarged or inflamed intestines with a color ranging from light to brown, with diphtheritic pseudomembranes and a bloody-brown watery fluid.

The classic “Turkish Towel” image is very typical, in which the surface of the mucosa of the small intestine acquires a rough appearance. Lesions are most commonly seen in the descending loop of the duodenum into the jejunum and occasionally in the ileum.

Healthy birds often have a low CP bacterial quantity in their intestines. For unknown reasons, the bacteria in healthy birds do not release toxins and may not cause symptoms or affect performance. However, when there is a change in the growth process, CP starts causing disturbances in their metabolism and causing problems.

As with other diseases where the cause is multifactorial, a single component cannot be singled out as the most important. However, there are significant indications that nutrition is one of the critical factors in the development and spread of the disease.

Unlike corn and soybean meal, small grains such as wheat, rye, and barley take on a high viscosity, moving slowly through the digestive tract and allowing rapid CP multiplication. Fishmeal and other animal products are also considered factors conducive to the development of necrotic enteritis.

A sudden diet change or distribution of the same (partial shortage of feed) could trigger an outbreak. Additionally, ingredients present in feed or water quality could also alter intestinal motility or damage the intestinal mucosa.

Other risk factors that increase the incidence of NE are the removal of litter between flocks, colder months (reduced ventilation/higher litter humidity), and, in general, poor housing conditions. In addition, the quality and health level of the eggs at the time of hatching, as well as the quality of the chick, could also be predisposing factors.

In countries where small grains are commonly used in chicken feed, the use of digestive enzymes helps reduce necrotic enteritis.

Products intended to promote a healthy microbiota, such as probiotics (containing Bacillus, Lactobacillus spp., etc.), competitive exclusion (CE) through indefinite cultures of chicken intestinal flora, complex carbohydrates (such as mannose), essential oils and organic acids have been shown to be beneficial, either alone or in combination, in reducing the incidence and detrimental effects of this condition.

Coccidiosis is probably the major predisposing factor for necrotic enteritis in broilers. Therefore, its control has become critical in broiler production systems that no longer use growth-promoting antibiotics and anticoccidial ionophores.

Immunization with live or attenuated coccidia vaccines is becoming more common practice as a method of controlled challenge. However, vaccines can cause slight damage to the intestinal epithelium. Litter moisture, incubation practices, temperature, ventilation, and sanitation also have a role in reducing coccidiosis and post-vaccination adverse reactions.

Increasing scientific evidence and field experiences suggest that a comprehensive preventive management program and the combined use of alternative products can mitigate the effects of coccidia and prevent the replication and production of toxins by C. perfringens.

Salmonella

Salmonellosis is one of the most common foodborne illnesses in the US, with estimated medical costs of $3.7 billion annually. Among foods of animal origin, poultry products are an important source of Salmonella.

Several salmonellae are found naturally in commercial flocks. Therefore considerable effort is being expended to reduce or eliminate their presence in poultry production, as well as in food processing, packaging, and preparation, to prevent their introduction into the food chain.

New standards for Salmonella in chicken and chicken parts, established in 2016 by the USDA Food Safety and Inspection Service, along with increasing pressure from suppliers and consumers, are forcing broiler producers to develop strategies to reduce the spread of Salmonella on production and processing systems.

The broiler industry can meet the challenge of reducing the presence of Salmonella by accepting one fundamental concept: Salmonella is a management problem. Therefore, the way in which the production system is managed on the farm will determine the success of reducing Salmonella in the processing plant.

There has been a significant increase, and the trend is likely to continue, in the number of alternatives and the availability of products to reduce Salmonella levels, many of which could be of great use.

• Avoid Entry: Control of Salmonella begins in the hatchery in breeders and broilers. It has been shown that the Salmonella serovars that infect chicks at an early age are often the same as those found later on. Therefore, employed control strategies are critical to reducing/eliminating exposure of breeder stock or hatchery to Salmonella or during the first days of chick life.

• Biosecurity: A biosecurity program should include management of risk factors, such as people and equipment movement, cleaning and disinfection, pest control (rodents/insects), and Biosecure building design.

• Feed: Feed and ingredients are a critical part of the program. Appropriate thermal and chemical treatment of feed, as well as dust control in the feed mill and insect/rodent control, are some of the most important aspects.

• Litter: Litter and litter moisture during the production cycle of the flock strongly impact the survival of salmonellae and their survival and multiplication in the soil. The management of the water distribution system is a key point for litter moisture control.

• Water: Water is a critical point to consider and can occasionally be a source of entry of Salmonella into the house, as well as a way for the bacteria to spread through it. Dust falling on open drinkers, and even on automatic drinkers, can be a form of contamination. Regular cloning with 3-5 ppm can reduce Salmonella transmission.

On-farm intervention methods include using probiotics (Lactobacillus spp. and Bacillus spp.) or competitive exclusion cultures obtained from normal chickens to take up residence in the gut to prevent Salmonella colonization.

Various prebiotics (organic acids, essential oils, complex carbohydrates, yeast-based extracts, etc.) can be digested by birds but are also used by commensal bacteria in the gut as an alternative to antibiotic growth promoters.

Recently, the combination of probiotics with prebiotics (symbiotics) has appeared on the market. The idea is that the probiotic is administered with a specific prebiotic that serves as a substrate to settle the probiotic in the intestine successfully.

Modified live Salmonella vaccines, in combination with inactivated Salmonella vaccines (bacterins), are commonly used in breeder flocks to prevent systemic Salmonella infections, reducing the risk of transmission to their progeny.

Multiple studies have shown that broilers from hens vaccinated against Salmonella have a lower prevalence at hatch, during growth, and before entering the processing plant.

The chicken intestine is a complex ecosystem with a delicate balance. Enteric diseases, such as coccidiosis, can upset this balance, negatively affecting the normal microbiota and allowing Salmonella to become a predominant part of the cecal microbiota. Therefore, all sections of the gut microbiota must be cared for to achieve optimal health and performance.

There is no single solution or program for the control of Salmonella. Most successful programs are those that use as many of the strategies and interventions listed above as practically and economically possible.

As we learn more, we will be able to minimize enteric diseases and have broilers that grow efficiently while providing a healthy and safe source for our consumers.