Question

Do you expect sheep that invest more in resistance to nematodes or tolerance of nematodes to be more likely to survive over the winter? Why?

Answer 1

The relative merits of resistance to nematodes and tolerance of nematodes as breeding goals depend upon the nature and epidemiology of the disease. Tolerance is expressed only when animals are infected. It provides an advantage over resistance as tolerance of infection place less selective pressure on the pathogen than resistance. Tolerance is not applicable to infection harbored by animals that cause disease in humans, it depends upon the prevalence of infection, it should never be decoupled from resistance within a breeding goal. In principle tolerance is applicable to nematode infection as these usually lead to a prevalence and nematode infections are not zootonic. The resistance to nematode infection is generally measured in terms of faecal egg count (FEC). By measuring resistance (FEC) and performance in a parasitised environment information is available to seek its benefits but the genomic modification may prevent or hinder the resistance ability to nematodes. But from tolerance, we can get the information of varying degree of nematode challenge and this information is used in many structural breeding programmes enabling estimation of genotype by environment interaction and determination of breeding goals to be customized by environment is necessary. So, with all these taken to count it is better to capture the benefits of tolerance to nematode infection for livestock. So sheep with tolerance of nematodes more likely to survive in winter.