Ducks are well known for being relatively resistant to diseases. There are no established vaccination plans for this species. They are considered potential carriers of infectious diseases from other birds and, therefore, farms are often isolated from other poultry farms. Some critical diseases in broiler production, such as coccidiosis or infectious bronchitis, are usually not as economically relevant in duck production. For this reason, this article presents the main challenges in duck production. The importance of such challenges regards to the species-specificity and/or their high prevalence:

• Toxins
• Locomotive problems
• Duck viral enteritis
• Riemerella anatipestifer infection
• Duck viral hepatitis

1. How do toxins affect ducks?

Ducks are especially sensitive to toxins, and high mortality cases related to toxicosis are common. The most common causes include botulinum toxin, lead, abusive use of antibiotics and mycotoxins.

Mycotoxins are secondary metabolites produced by fungi. Signs vary on severity and chronicity depending on time and amount of exposure. Mycotoxins are one of the main challenges in duck production. The toxicity of mycotoxins in ducks has not been studied as much as in broilers, despite their high sensitivity to these molecules.

Ducks are especially sensitive to aflatoxins because they metabolize this molecule differently from other species (more bioactivation of the molecule and less detoxification and elimination than in broilers). Furthermore, the presence of various mycotoxins in feed, which is very frequent, is especially dangerous for this species. The immune system and internal organs, such as the liver, are the most affected by the presence of mycotoxins in duck feeds.

The harmful effects of toxins in ducks need to be considered to prevent their effects. Regarding mycotoxins, it is important to carry out a quality control of the feed and raw materials, as well as to include a mycotoxin binder in feed formulation.

2. Locomotive problems in ducks

Ducks are aquatic animals whose anatomy is adapted to propulsion in water rather than to support their weight on land. Furthermore, the current breeding is focused on early muscle development. Then, the muscle development does not coincide with the skeletal development of the animal.

Locomotor problems are one of the main challenges in duck production. Lameness, dislocations and broken bones are common, due to the rearing of heavier animals. Locomotive lesions may condition the mobility of affected animals. The material and condition of the litter can create a sliding surface that increases the incidence of these lesions.

Other common problems related to the weight of the animal and the litter condition include tibial dyschondroplasia and bacterial infections in the hocks.

The rapid growth of the animal in intensive breeding can also cause other problems, such as ascites. Ascites occurs when there is a disproportion between the growth of the animal and the growth of the heart and lungs, which hinders the supply of oxygen from these organs to the organism.

3. Viral Enteritis of de ducks

Duck viral enteritis, also called duck plague, is a contagious and fatal condition caused by a herpesvirus. It can affect animals of all ages, although it usually affects ducks over 5 weeks old. The severity of the disease increases with age. Therefore, it has an important economic repercussion in adult ducks farming.

It is transmitted orally between infected animals or through water. The presentation of the disease and mortality vary depending on the age of the animal, the immune status and the virulence of the virus.

The first signs observed are usually high and persistent mortality in susceptible flocks. If there is partial immunity, deaths are occasional and the presentation tends to be chronic. The acute presentation includes sudden death, photophobia, nasal discharge, polydipsia and watery or bloody diarrhoea. Young animals may show dehydration and weight loss and lower mortality. In laying hens, a considerable decrease in egg production is observed.

Affected animals show haemorrhagic lesions and necrosis in internal organs (such as the heart and liver) and throughout the gastrointestinal tract. Haemorrhagic lesions in the digestive system can evolve and coalesce, and the mucosa may appear covered with a diphtheritic membrane. It also affects the lymphoid organs, which show necrotic degeneration.

Birds that survive the disease might still be carriers and act as reservoirs of the virus, excreting it in the faeces for a long period of time, contaminating eggs surface.

There is no treatment available for this disease, so prevention methods are essential. Prevention is based on correct biosecurity measures to maintain a disease-free environment, and immunization of the breeding and commercial flocks with live attenuated vaccine. Vaccines available can be administered intramuscularly or subcutaneously.

4. Infection with Riemerella anatipestifer

Riemerella anatipestifer is a bacterium that causes an infection with high morbidity and mortality in susceptible flocks. It has a similar presentation to that of Pasteurella spp. infections.

It can affect ducks of all ages, although it is more frequent in young animals and farms where animals of different ages are present at the same time.

Transmission of the disease is not clearly defined, although it is believed that animals can be infected by aerosol and through wounds in the feet. Therefore, the lack of hygiene in the farm provides the ideal environment for the spread of the illness. The disease can become endemic once there is an outbreak in the farm.

Affected animals may show diarrhoea, eye and nasal discharge, respiratory signs, such as coughing and sneezing, and nervous signs including incoordination, tremors, paralysis and seizures. The disease can be fatal. Mortality is variable (5-50%), although it can reach 75%.

Observed lesions can include the presence of inflammation with fibrinous exudate in the pericardium, liver and air sacs. Pneumonia, purulent synovitis, fibrinous meningitis, and caseous salpingitis may also appear.

Disease prevention is based on the maintenance of a high level of biosecurity in the farm and the correct cleaning and disinfection between flocks. It is also important to avoid the contact between animals of different ages.

In addition, live vaccines and bacterins have been used for immunization of breeding and commercial production. Although commercial vaccines usually include the three most common serotypes, vaccination has its limitations, since this bacterium has numerous serotypes without cross immunity.

5. Viral hepatitis of the duck

Duck viral hepatitis (DVH) is a highly contagious notifiable disease of great economic importance.

DVH is caused by three genotypes of the duck hepatitis A virus, a picornavirus. The most pathogenic and disseminated genotype is DVH type I, while DVH-2 and DVH-3 genotypes have subsequently been identified as etiological agents of the disease. These genotypes do not differ in the clinical picture and lesions shown, and they are only differentiated through laboratory diagnostic techniques.

Susceptible animals are under 6 weeks old, mainly young ducks up to 30 days of age. The younger the animal, the most susceptible it is to the disease. Adult birds show no clinical signs. The virus spreads rapidly and horizontally. Morbidity can reach a 100%. The entire flock can be affected within a few days, causing high flock mortality, up to 95%.

The disease has a peracute presentation, since death usually occurs within hours after the onset of the clinical signs. Clinical signs may include lethargy, ataxia and spasmodic contractions, followed by opisthotonos and death.

Lesions caused by the disease include hepatomegaly, haemorrhages and/or necrosis of the liver. Splenomegaly and renal swelling may also be seen.

The prevention of this disease is based on the vaccination of the breeding stock with live attenuated vaccine to induce passive immunity to the offspring.

6. Conclusions

Ducks are well known for being relatively resistant to diseases, although there are different main challenges in duck production. The main challenges in duck production may be of infectious origin or caused by mismanagement.

Management problems include locomotive problems and ascites. Therefore, it is essential to have good control over the growth of animals, but also to maintain a proper condition of the litter to reduce both physical and infectious risks.

In addition, it is basic to assess the quality of the feed to avoid the presence of infectious agents and mycotoxins in the feed. This evaluation should be done because of the effect of pathogens and mycotoxins on the productivity of the animals, as well as its immunosuppressive effect, which can favour the appearance of secondary diseases. The inclusion of a mycotoxin binder in feed reduces the risk of exposure to mycotoxins and their effect.

Regarding infectious disorders, it is essential to carry out a correct biosecurity plan to prevent contact of wild animals with the flock, feed and drinking water, as well as a proper cleaning and disinfection of the facilities. It is also important to avoid the contact between animals of different ages. When there is a high challenge, it is recommended to establish a vaccination plan to fight the disease.

The use of immunostimulant products allows animals to maintain a proper immune status and achieve a better immune response after vaccination and, therefore, greater protection against disease.

To sum up, the control of the main challenges in duck production is based on good management practices and biosecurity measures, as well as the application of a vaccination plan and the use of natural solutions, like mycotoxin binders and immuneboosters.