IMPORTANT: If you reside in a country where health product communications are restricted to health care professionals, and you are NOT a health care professional, please contact your veterinarian instead of reading the following information.

Optimizing Poultry Enteric Health*


Gastrointestinal integrity is a cornerstone of poultry health and productivity, underlying many important factors of production: growth, feed efficiency, carcass quality, food safety. Numerous avian pathogens can disrupt normal digestive processes and cause a variety of symptoms, impeding birds’ growth and bringing 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.


Disease Management Approaches

Enteric disorders in poultry can be a challenge to identify and treat, since multiple pathogens are often involved, and many diseases present with similar 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 pathogen strains are asymptomatic in poultry but can cause severe illness in humans from food consumption, like Salmonella or Campylobacter.

Since most pathogens are transmitted through feces and oral ingestion, hygiene and sanitation are of utmost importance in disease control. Traditionally, enteric diseases were treated most commonly with anti-parasitic or anti-bacterial medications, often in feed additives. These approaches are still used, but with changing regulations and consumer demands to reduce drug residues in food production systems, prophylactic vaccination has become an increasingly important tool in this area of poultry health.


Merial’s Solutions**

In the U.S., Merial is already one of the industry leaders in coccidiosis vaccination, and we anticipate sharing this expertise with wider markets as the poultry industry evolves. With the increasing importance of vaccination for other enteric diseases, including malabsorption syndrome originated by Reovirus infections, especially in broilers, Merial’s legacy in biologics guides our focus on developing alternative solutions to the traditional pharmaceutical approaches. Currently, our enteric product portfolio* includes the following brands:

  • HATCHPAK Cocci III, our live vaccine marketed in the U.S.** for hatchery administration to aid in the prevention of several strains of coccidiosis
  • GALLIVAC SE, a live vaccine (available in certain markets**) to help control salmonella
  • GALLIMUNE, our line of inactivated vaccines (available in certain markets**), including products for salmonella (GALLIMUNE SE + ST) and for reovirus
  • BURSA GUARD REO (available in certain markets**) to help control avian reovirus in combination with infectious bursal disease
  • Autogenous vaccines produced upon request for individual poultry producers in the U.S.** from specific salmonella strains isolated at their sites

Brand and product availability varies from region to region, but we are always evolving our portfolio to address new challenges, changing regulations, and industry concerns.

Our customer solutions also include the expertise of our Veterinary Services teams. These avian health specialists are closely attuned to regional epidemiologies and bring deep knowledge of diagnostic tools, vaccine compatibilities, and poultry business goals. Let us help you develop a customized vaccination program to optimize your flock’s enteric health.


Key Poultry Enteric Diseases*

IMPORTANT: Following are the top enteric diseases that Merial currently focuses on, but be aware that we do not offer products for all these diseases in all regions. To learn about complete product options in your country, talk to your current Merial representative or contact us.



Caused by a parasitic protozoa called Eimeria (Eimeria maxima, acervulina, tenella, necatrix, etc.), coccidiosis infects and damages various parts of the intestinal tract in chickens and other types of poultry. There are many different Eimeria strains, which affect different species of birds and even specific regions of the gut. Coccidia is widely found in poultry operations, and disease occurs when birds ingest large numbers of the parasite’s eggs (called “oocysts”), which then reproduce in the gastro-intestinal tract. Signs can vary, depending on the Eimeria species involved, and range from poor growth and feed conversion to severe clinical disease, including loss of appetite, bloody diarrhea, and high mortality. Even if birds recover, they may never catch up on lost growth and productivity. Sub-clinical forms can still increase susceptibility to other infections.

Eimeria oocysts are shed through birds’ feces and can persist for long periods in the environment; good hygiene can help, although some species may be resistant to disinfection. Traditionally, anti-parasitic drugs (coccidiostats), usually in the form of feed additives, are given to prevent disease. But increasingly, vaccination has become a more widely used approach in order to induce immunity early in chicks or young birds. Many countries implement a rotating program, alternating between coccidiostats and vaccination. Merial has focused extensively on coccidiosis control and currently markets a live oocyst vaccine in the U.S. market** to aid in the prevention of the disease.

Top Merial products:** HATCHPAK COCCI III


Salmonella Infection (Salmonellosis)*

Salmonella, the most common cause of food-borne illness in people, is a large group of bacteria that live in the intestinal tracts of many animals. There are several strains found in commercial poultry; the most significant are the Salmonella enterica serovars enteriditis and typhimurium, since these are the two main serovars implicated in human illness from consumption of eggs (most commonly) or poultry meat. Merial currently offers vaccines in certain markets** for control of these Salmonellas, and we are focused on playing a growing role in this important issue for the poultry industry. 

Top Merial products:** GALLIMUNE SE + ST; GALLIVAC SE; autogenous (U.S. only)

More on our Solutions for Food Safety


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 and runting stunting syndromes. Direct causality is not always clear, as multiple pathogens are often implicated in 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. Limited vaccines are available in some markets, although vaccination has not yet become a widespread protocol industry-wide.

Some of the most important of these virus groups include:

  • Avian reoviruses are a widespread group of viruses that can interact with other infectious agents of chickens, including E. coli and infectious bursal (Gumboro) disease, to cause clinical signs, including stunted growth and poor feed conversion, especially in broiler birds. Vaccination and good hygiene practices can help reduce the impact of these viruses on the commercial poultry industry. Merial offers live and inactivated vaccines in some markets** to help prevent infection by reovirus. 

       Top Merial products:** GALLIMUNE range; BURSA GUARD REO

  • Turkey enteric coronaviruses spread rapidly and cause viral enteritis, an acute disease with significant economic impact. Mortality rates can be high, and birds that do survive experience depressed growth. The virus has been found at commercial turkey operations in many countries, and while identified as the primary cause, the disease is often complicated by co-infections. Vaccination is not currently available, but strong biosecurity and hygiene can aid in disease control.
  • 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. There is currently no treatment or vaccination, but birds may be treated for dehydration and secondary infection, if present.


E. Coli Infection (Colibacilliosis)

Escherichia coli, more commonly known as E. coli, is a common bacterium found in the intestinal tract of many animals, including poultry, although its impact goes far beyond enteric health. Most avian strains are harmless, but some virulent strains can cause severe disease—known as colibacilliosis—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 adversely affects the performance of surviving birds, making it economically significant within the poultry industry.

E. coli is an opportunistic bacteria, and any weakness in the bird—including other diseases, immunosuppression, or environmental stressors—can increase susceptibility to E. coli infection. Some bacterin-based vaccines have been used to protect against E. coli, but maintaining overall flock health and preventing other diseases is perhaps the most important measure for preventing colibacilliosis.


*Merial produces and markets several vaccines against poultry enteric diseases. However, be aware that NOT all aspects of the diseases mentioned on this page are addressed by a vaccine. Always consult the product label for exact vaccine indications.

**Many of Merial’s avian vaccines are only marketed and available in certain countries, sometimes under different trade names. Speak to your Merial representative or contact us to find out what’s available in your region.


To find out exactly which Merial avian products and vaccination equipment options are available in your region, talk to your Merial representative or contact us now.

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