Host resistance and infectivity are genetic traits affecting infectious disease transmission. Unsurprisingly, it is receiving more and more attention from livestock breeders. A single allele is responsible for adhesion factors receptors in the host gut, which allows binding and infection of various E. Two induced mitogynogenetic doubled haploid F2 rainbow trout Oncorhynchus mykiss families were used. The combined procedure was efficient for high resolution mapping. The loss in fitness advantage may limit the success of selection for resistance, and simulations have shown that selection for resistance results in polymorphisms instead of fixation of resistant alleles in the host Roy and Kirchner, ; Miller et al.
If looking at a non-labile trait practically fixed during some period and not easily changeable , more observations across multiple individuals need to be used compared to when investigating a labile trait an easily adjustable trait e. Currently there is sufficient preliminary information available on relevant genetic parameters for footrot resistance, as well as its correlations with other production traits, to include resistance to footrot in sheep-breeding programmes. Animals were naturally infected with Haemonchus contortus, Teladorsagia circumcincta, Oesophagostomum spp. The model was developed from an equation that describes the probability of an individual to become infected as a function of its own susceptibility genotype and infectivity genotypes of all its infected group mates. The book is rich in technical jargon. Problems caused by native pathogens are likely to arise as a consequence both of rapid climate change and of forest management practices that lead to increases in species density, drastic reductions in genetic diversity and planting outside the native range.
It may not be feasible to record true tolerance using routinely collected on-farm data. In addition, it may be useful to quantify tolerance to environmental effects across different genotypes, hence the need to investigate g × e interactions, and possibly g × d × e interactions. There are few published estimates for these parameters, but plausible values for the rate of recovery would result in a response to selection, in terms of changes in the observed prevalence, double that predicted by purely genetic models in the medium term e. Major advances in the study of inheritance were made in the early 20th century that became the basis for the systematic improvement of chickens for specialised egg or meat production in the last 50 years. Resistance and tolerance are usually considered as static traits.
However, there is also a type of animal disease that straddles these two categories. Since there is no adverse effect on the pathogen, selection for tolerance allows animals to be a source of infection for susceptible animals and may result in an increase in transmission of infection. In order to clarify if resistance and tolerance are simply different expressions of the same trait, or indeed are genetically different traits, we first need to estimate the genetic correlation r G between these two traits, with different traits indicated by an r G of less than one. Cosegregation of porcine malignant hyperthermia and a probable causal mutation in the skeletal muscle ryanodine receptor gene in backcross families. One promising approach for the improvement of health in livestock is the selection of resistant or tolerant animals. Effect of selection against deleterious mutations on the decline in heterozygosity at neutral loci in closely inbreeding populations. Genetics of resistance to mastitis in dairy cattle.
Inherited disorders: sustained attack from several quarters. The evolution of plant response to herbivory: simultaneously considering resistance and tolerance in Brassica rapa. Ecological immunology and tolerance in plants and animals. Neither of these authors discusses whether a general or robust immunity will be beneficial for maintaining health and productivity across varying infection levels. As with so many other areas of animal breeding, exceedingly valuable insights into practical issues can be gleaned from a critical evaluation of population and quantitative genetics research that has been conducted in the broader sphere of evolution. Chapter: 10 Page no: 213 Author s : Lamont, S.
Moreover, this number is rapidly growing. Chapter: 8 Page no: 166 Author s : Moen, T. The book will be an essential reference for professionals in the field, scientists and researchers, students, breeders, vets, agricultural advisors and policymakers. Mutations have been occurring ever since species existed, and germ-cell mutations have been giving rise to inherited disorders for just as long. Traits that ameliorate the damage caused by the pathogen itself, or the damage caused by the host response such as inflammation need to be examined in order to quantify tolerance. Understanding the role of host genetics in disease spread is important for developing disease control strategies that efficiently reduce infection incidence and risk of epidemics.
The environment of the pig may be a determinant of disease manifestation, and although its control to meet pig requirements improves production and reduces stress Black et al. Eye infection may incur economic losses to producers due to reduced selection intensity, but ethical aspects need to be considered as well because eye infection can be quite painful and reduce animal well-being. The result would be a multidimensional model. A general framework to model the relationship between these variables and possible outcome measures is also described. Its coverage includes: parasites and vectors; bacterial diseases; viral and subviral diseases; and production diseases.
Both natural and managed forests are currently suffering from increases in damage by pathogens. This need exists irrespective of whether one is concerned with the purely practical aspects of breeding crop plants for resistance to disease, or whether one is probing the genetics and biochemistry of resistance and susceptibility. The response variable to quantify tolerance may be based on performance measures, health status, and survival of pigs. Indeed, he has already dabbled with this topic ; ;. Chapter: 4 Page no: 57 Author s : Hunter, N.
Mathematical models are therefore required to predict the effect of genetic and epidemiological changes on disease incidence. On the other hand, there are several important zoonotic diseases, which their severity and transmission could be affected by genetic similarity of human and host animal, because disease resistance could be noticeably affected by genetic factors Bishop et al. However, the higher heritability estimates of 0. Selective breeding for sea lice resistance should reduce the impact of sea lice on fish health and thus substantially improve the sustainability of Atlantic salmon production. Clearly an absence of genotype-by-environment interaction is preferred so that animals would remain healthy across varying environments and pathogenic challenges.
However, it may not always be possible to make a clear distinction between the two mechanisms. The genotype set may also comprise of a single pig, if multiple measures are available for a pig that experiences varying environmental conditions. In this paper we propose that one feasible and fair way to address this problem is to tax animal products obtained with the use of antibiotics. . We outline evidence in support of this hypothesis and describe methodologies for detecting and estimating genetic parameters for infectivity.