Gastrointestinal integrity is a cornerstone of poultry health and productivity, underlying many important factors of production, including growth, feed efficiency, carcass quality, and food safety. Numerous avian pathogens can disrupt normal digestive processes and cause a variety of symptoms, impeding birds’ growth and causing economic losses. Historically, bacteria and parasites have been considered the primary causes of enteric problems in poultry, but in recent decades more attention has been paid to the role of viruses as well. Today’s poultry producers are looking for effective solutions to control important enteric diseases while adhering to evolving regulations and consumer demands.
The Impact of Diseases on Enteric Health
Enteric disorders in poultry can be a challenge to identify and treat, since multiple pathogens are often involved and many diseases present with similar clinical signs, including stunted or abnormal growth, poor feed conversion, increased water intake, diarrhea, and enteritis (inflammation of the intestinal tract). Mortality rates vary widely. Sub-clinical disease is common and may still adversely affect production parameters. In addition, some microorganisms, like Salmonella or Campylobacter, are non-pathogenic in poultry, but can cause severe illness in humans from food consumption. Since most pathogens are transmitted through feces and oral ingestion, hygiene and sanitation are of utmost importance in disease control.
Coccidiosis is the most common protozoal disease in poultry and a top contender for annual economic loss in the poultry industry. These microscopic, single-celled organisms of the genus Eimeria invade the intestinal wall of poultry and cause damage as they reproduce. There are many different species of poultry coccidia, which are host-specific and even affect specific regions of the gut. Coccidia are ubiquitous in poultry operations. Disease occurs when naïve birds ingest large numbers of the parasites’ eggs (called “oocysts”), which then reproduce in the gastro-intestinal tract.
Oocysts, shed in the feces of both recovered and clinical birds, contaminate the poultry house environment. Oocysts can be transmitted by mechanical vectors (e.g., humans/clothing, insects, equipment, and other animals, particularly rodents). Oocysts are not initially infective and must undergo sporulation over a 1-2 day period in ideal moisture, oxygen, and temperature (70°–90°F [21°–32°C]) conditions. These oocysts can persist for long periods in the environment.
All ages of poultry are susceptible to the disease if not previously exposed, although the most susceptible to coccidiosis are usually young, naïve chicks. Among different species and breeds of poultry, there are considerable differences in susceptibility to the disease.
Clinical signs can vary depending on the coccidial species involved and range from poor weight gain and poor feed conversion to severe clinical disease, including loss of appetite, ruffled feathers, blood or mucus in feces, and high morbidity or mortality. Even if birds recover, the negative impacts on weight gain, feed conversion, and performance cannot be offset. Sub-clinical coccidiosis forms can still increase susceptibility to other infections, such as Clostridium spp.
Salmonella Infection (Salmonellosis)*
Salmonellosis caused by Salmonella spp. is one of the most important zoonotic diseases and is transmitted to humans through raw food animal products, including poultry meat. It is a large group of bacteria that live in the intestinal tracts of many animals. The most significant are the Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Typhimurium, since these are the two main serovars implicated in human illness.
Enteric-Associated Viral Infections*
In recent years, several types of viruses have been identified in the gastrointestinal tracts of poultry and have come to be associated with some of the industry’s most problematic and costly enteric diseases, including malabsorption, runting, and stunting syndromes. Direct causality is not always clear, as multiple pathogens are often implicated at the onset of disease. The viruses are found in birds of all ages, although younger birds are most susceptible to disease and most impacted by poor growth parameters.
Some of the most important of these virus groups follow.
Avian reoviruses are a widespread group of viruses that can interact with other infectious agents of chickens, including E. coli and infectious bursal disease (Gumboro disease), to cause clinical signs including stunted growth and poor feed conversion, especially in broiler birds.
Avian rotaviruses are found in many species of birds, and infection is associated with enteritis (inflammation of the intestinal lining) and diarrhea, especially in younger birds. Infected birds often have stunted growth and are severely dehydrated, which can lead to death. The virus is transmitted orally and good hygiene can reduce infection.
E. Coli Infection (Colibacillosis)
Escherichia coli, more commonly known as E. coli, is a common bacterium found in the intestinal tract of many animals, including poultry. The impact of E. coli infection goes far beyond enteric health. Most avian strains are harmless, but some virulent strains can cause severe disease – known as colibacillosis – when large amounts of the bacteria invade the bird’s body beyond the gastrointestinal tract. Clinical signs vary widely, since E. coli attacks many different tissues and organs. It can be fatal, and it adversely affects the performance of surviving birds, making it economically significant within the poultry industry.
E. coli is an opportunistic bacterium. Any weakness in the bird – including other diseases, immunosuppression, or environmental stressors – can increase susceptibility to E. coli infection.