The health, welfare, and production of ruminants, as well as the quality of food resources, are all affected by gastrointestinal parasites. Even with all the traditional ways to keep diseases under control, parasites still hurt the livestock industry. Controlling disease carriers and using the right management methods are two ways to reduce these negative effects. But there are often things that make it hard for these disease-control strategies to last, like the effects of chemicals on the environment and food safety, the cost and availability of treatments for poorer livestock farmers, and the development of parasites that are resistant to the treatments.
Considering the economic effects of parasites on the health and welfare of livestock, it is better to avoid parasitic infections than to treat them. Different environmental and host factors, some metabolic diseases, the host’s immune status, and pregnancy or lactation all affect how resistant ruminants are to parasites that live in their guts. So, one way to deal with this problem is to study the genetics of disease resistance, which includes both immune and non-immune mechanisms.
Not getting sick
Disease resistance is an animal’s natural ability to fight off disease when it is exposed to pathogens or parasites for the first time. It looks at how well the host can control the pathogen or parasite’s life cycle and how resistant it is to the disease that comes from an infection. Natural resistance is passed down from parent to child. Using selective breeding programmes to increase the overall level of genetic resistance in a population can improve animal health management systems.
Why genetics is good
Some of the benefits of using genetics to control disease are that once a change is made, it is permanent, the effect is consistent, and there is no longer a need to buy inputs. Also, the effects of other methods last longer because there is less pressure for resistance to develop.
There are also possible broad-spectrum effects, such as making people more resistant to more than one disease, having less of an effect on the evolution of macroparasites like helminths than other strategies like chemotherapy or vaccination, and making disease management strategies more varied.
Management strategies
Diseases can be managed genetically in different ways, depending on the kind of problem and the resources that are available. Some of these methods are choosing the right breed for the production environment, crossbreeding to add genes to breeds that are already well-suited for the job, and choosing individuals with high disease resistance.
There are breeding programmes that pick out animals that are more resistant to diseases like parasite infections and some types of mycotoxin poisoning. If we can find genetic markers that are linked to resistance to infection, we might be able to choose for more resistance even when there is no infection.
Marker-assisted choice
Marker-assisted selection is a method in which a marker based on morphology, biochemistry, or DNA/RNA is used to indirectly select for a trait of interest, such as disease resistance. Because genes are linked, the marker used for selection is often linked to the gene of interest. There are selectable markers, which get rid of certain genotypes from the population, and screenable markers, which make certain genotypes easy to spot, at which point the experimenter must score or evaluate the population and take action to keep the preferred genotypes.
Marker-assisted selection may be cheaper and faster than traditional phenotypic assays, depending on the trait of interest. Using the same DNA sample, more than one marker can be tested. Once the DNA is extracted and cleaned, it can be used for more than one marker, for the same or different traits, which saves time and money per marker.
Identifying markers
Molecular techniques like microsatellites or single nucleotide polymorphism detection can be used to find genetic markers. Linked markers are molecular markers that are right next to important genes. There are a number of phenotypic and genetic markers for resistance to parasites in the digestive tract of naturally infected ruminants. These could help ruminants respond to selection.
The major histocompatibility complex (MHC) is made up of a group of genes that are very different from one another. These genes start the immune response when pathogens or parasites attack an animal. The MHC is split into three regions: class 1, class 2, and class 3. In ruminants, the class 2 region is split into two parts: class 2a and class 2b.
Choosing which characteristic to measure
The faeces egg count (FEC) is used as a sign of resistance to parasites in the digestive tract. It was first made for sheep, but it can also be used for cows, pigs, chickens, and other species. The FEC can be passed down in many different ways, depending on the type of parasite and the animal breed. The immune response is another trait that can be used as a sign.
Breeding by choice
One important way to stop diseases is to use selective breeding to take advantage of differences in disease resistance within the same breed. When parasite resistance is the only thing that is chosen for, it can lead to bad traits like lower live-weight gains. To predict genetic risk or use selective breeding, it is important to use the right selection policies and understand the genetic structure of the resistance.
Conclusion
In the long run, a different way to get rid of parasites is to use selective breeding for resistance to parasites along with other integrated control methods. However, disease resistance varies between species, between breeds and between individuals within breeds. It is hard to find the phenotype for disease resistance because a population may have both healthy and sick animals, and not all of the healthy animals may be resistant to disease.
