Genetic resistance to gastrointestinal parasites - Poultry World

Genetic resistance to gastrointestinal parasites – Poultry World

Gastrointestinal parasites negatively affect the health, welfare, production and quality of feed resources of all farmed species, and despite all traditional disease control systems, they continue to hamper the industry of breeding.

Approaches such as disease vector control and appropriate management methods help reduce these adverse effects. However, there are often constraints on the sustainability of these disease control strategies, such as the environmental and food safety impacts of chemical treatments, the affordability and accessibility of treatments for poorer livestock keepers, and the evolution of the resistance of parasites to treatments.

Given the economic, health and social impacts of parasites on the livestock industry, prevention has more benefits than cure for parasitic infections. Different environmental and host factors, certain metabolic diseases, and host immune status can affect an animal’s resistance to gastrointestinal parasites. Therefore, the genetics of disease resistance involving immune and non-immune mechanisms is one approach to this question.

What is disease resistance?

Disease resistance is defined as the inherent ability of a previously unexposed animal to resist disease when attacked by pathogens or parasites and is considered the host’s ability to moderate the life cycle of the pathogen or parasite, and its resistance to the pathological consequence of infection.

Natural resistance is inherited and passed from parent to offspring. Therefore, increasing the overall level of genetic resistance in a population through the use of selective breeding programs could improve animal health management systems.

Benefits of Genetic Disease Resistance

Advantages of incorporating genetic elements into disease management strategies include permanence of genetic change once established, consistency of effect, no need for purchased inputs once Once the effect is established, the effectiveness of other methods is prolonged as the likelihood of emergence of resistance is reduced.

In addition to this, there is the possibility of broad-spectrum effects and increased resistance to more than one disease, as well as having less of an impact on the evolution of macro-parasites, such as helminths, compared to other strategies (such as chemotherapy or vaccination), and this adds to the diversity of disease management strategies.

Application of genetic management strategies

The application of different strategies to genetic disease management depends on the nature of the problem and the resources available. These approaches include choosing the appropriate breed for the production environment, breeding to introduce genes into breeds well suited for the required purpose, and selecting individuals with high levels of disease resistance.

There are breeding programs that focus on breeding commercial animals for increased resistance to certain diseases, such as parasitic infections and some forms of mycotoxin poisoning. The discovery of genetic markers associated with resistance to infection potentially allows selection for increased resistance in the absence of infection.

Marker assisted selection

Marker-assisted selection is a process in which a morphological, biochemical, or DNA/RNA-based marker is used for indirect selection for a trait of interest, such as disease resistance. The marker used for selection is associated with a high frequency with the gene of interest due to genetic linkage. There are selectable markers that eliminate certain genotypes from the population and screenable markers that make certain genotypes easily identifiable, in which case the experimenter must mark or score the population and act to retain the preferred genotypes.

Depending on the trait of interest, marker-assisted selection can be cheaper and faster than conventional phenotypic testing. Multiple markers can be assessed using the same DNA sample, and once the DNA has been extracted and purified, it can be used for multiple markers for the same or different traits, reducing time and the cost per marker.

Identify genetic markers

Genetic markers can be identified by a range of molecular techniques, such as microsatellites or single nucleotide polymorphism detection. Linked markers are molecular markers located very close to the major genes of interest. There are several known phenotypic and genetic markers for resistance to gastrointestinal parasites in naturally infected animals that could potentially contribute to the selection response.

The major histocompatibility complex (MHC) involves a series of highly polymorphic genes that are responsible for initiating the immune response when an animal is attacked by pathogens or parasites. The MHC is divided into 3 regions: Class 1, Class 2 and Class 3.

Fecal egg count (FEC) is used as an indicator trait to determine resistance to gastrointestinal parasites. The heritability of FEC varies considerably by parasite species and animal breed. Immune response assessment is another indicator trait that can be used.

Selective breeding

Selective breeding to take advantage of within-breed variation in disease resistance is an important disease control strategy. Breeding solely for parasite resistance can result in negative traits, such as lower liveweight gains. Therefore, applying appropriate breeding policies and understanding the underlying resistance genetic architecture is essential to predict genetic risk or selective breeding.

The application of selective breeding for parasite resistance in combination with other integrated control methods is considered an alternative means of long-term parasite control. However, disease resistance varies between species, between breeds and between individuals within breeds, and identification of the disease resistance phenotype is difficult, because in a population containing both healthy and diseased animals, all healthy animals cannot be disease resistant.

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