PHOTO: JAN WILLEM SCHOUTEN


HEAL ▶▶▶TH


Genetic resistance to gastrointestinal parasites


Gastrointestinal parasites can play havoc in the digestive tract of all animal species, causing a lack of appetite, diarrhoea and poor growth, leading to economic losses for the farm. Selective breeding for parasite resistance in combination with other integrated control methods is considered an alternative means of parasite control.


BY SAMANEH AZARPAJOUH G


astrointestinal parasites negatively affect all livestock species’ health, welfare, production and the quality of food resources, and despite all the traditional disease control systems, they continue


to hamper the livestock industry. Approaches such as the control of disease vectors and appropriate management methods help to reduce these adverse effects. However, there are often constraints on the sustainability of such disease control strategies, like the environmental and food safety-re- lated impacts of chemical treatments, the affordability and accessibility of treatments to poorer livestock producers, and the evolution of parasite resistance to the treatments. Consid- ering the economic, health and welfare impacts of parasites on the livestock industry, prevention has more advantages than curing parasitic infections. Different environmental and host factors, some metabolic diseases and host immune status can affect an animal’s resistance to gastrointestinal parasites. Therefore, the genetics of disease resistance involv- ing immune and non-immune mechanisms is an approach to this issue.


What is disease resistance? Disease resistance is defined as the inherent capacity of a previously unexposed animal to resist disease when chal- lenged by pathogens or parasites and is considered as the host’s ability to moderate the pathogen or parasite lifecycle, and its resistance to the disease consequence of infection.


26 ▶ POULTRY WORLD | No. 7, 2022


Natural resistance is heritable and transmissible from par- ent to offspring. Therefore, increasing the overall level of genetic resistance of a population through the use of se- lective breeding programmes could improve animal health management systems.


Advantages of genetic disease resistance The benefits of incorporating genetic elements in disease management strategies include the permanence of genetic change once it has been established, the consistency of the effect, the absence of the need for purchased inputs once the effect is established, the effectiveness of other meth- ods is prolonged as the likelihood of resistance emerging is reduced. On top of this there is the possibility of broad spectrum effects and increasing resistance to more than one disease, as well as having less impact on the evolution of macro-parasites, such as helminths, compared to other strat- egies (such as chemotherapy or vaccination), plus it adds to the diversity of disease management strategies.


Application of genetic management strategies Applying different strategies to the genetic management of diseases depends on the nature of the problem and the resources available. These approaches include choosing the appropriate breed for the production environment, cross- breeding to introduce genes into well-adapted breeds for the required purpose, and selection for individuals with high levels of disease resistance. There are breeding programmes focused on selecting commercial animals for enhanced resist- ance to some diseases, such as parasite infections and some forms of mycotoxin poisoning. Finding genetic markers asso- ciated 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 morpholog- ical, biochemical, or DNA/RNA-based marker is used for indi- rect selection of a trait of interest, such as disease resistance.


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