Polymorphism of the IGHA gene in sheep

Prevalence and resistance to gastrointestinal parasites in goats: A review

Gastrointestinal parasitism, particularly nematode infection, is a major health issue affecting goats worldwide, resulting in clinical diseases and productivity loss. Prevalent gastrointestinal parasites (GIPs) affecting goats in South Africa are the Strongyloides papillosus, Eimeria spp., and Strongyles, especially the Haemonchus contortus and Trichostrongylus spp. According to the issues discussed in this paper and by other authors, the prevalence and intensity of various GIPs vary with an animal's location, breed, age, sex, and season. Because GIPs easily develop resistance to chemical treatment, selecting and breeding genetically GIP-resistant animals would be a relatively simple and inexpensive strategy for reducing or eliminating the current reliance on chemotherapy. Potential phenotypic indicators for selecting GIP-resistant goats include parasitological, immunological, and pathological phenotypic markers. Synergistic use of these indicators should be encouraged for a more accurate simplified genotype selection of resistant animals. Genes with Mendelian inheritance, particularly those involved in immunoregulatory mechanisms, have been identified in goats. Exploring this knowledge base to develop cost-effective molecular tools that facilitate enhanced genetic improvement programs is a current challenge. Future statistical and biological models should investigate genetic variations within genomic regions and different candidate genes involved in immunoregulatory mechanisms, as well as the identification of single nucleotide polymorphisms known to affect GIP infection levels.

Small ruminant resistance against gastrointestinal nematodes: a case of Haemonchus contortus

Gastrointestinal nematode (GIN) infections are a common constraint to small ruminant industry throughout the world, and among those, haemonchosis has its own significance. Control of GIN primarily relies on the use of anthelmintics, but this approach has become less reliable due to the development of resistance in GINs against commonly used anthelmintics and an increased consumer demand for environmentally friendly animal products. These issues have stimulated investigations to find alternative sustainable control strategies, which are less reliant on anthelmintic input. One of such strategies is breeding of small ruminants for their resistance to the GINs. The susceptibility and resistance of animals to GIN infections varies within and between breeds. Various parasitological, biochemical and immunological parameters are employed to evaluate natural resistance status of animals both in natural pasture and artificial infections. The immune mechanisms responsible for resistance are not completely understood, but it has a significant effect in inherited resistance. Relatively resistant or tolerant animals show better local and generalised immune response as compared to susceptible. Immune response against GINs is influenced by many physiological factors. Determination of specific genes linked with host resistance will provide a valuable approach to find out the molecular mechanism of host resistance to GINs. Resistance has been reported to reduce pasture contamination, which in turn reduces re-infection and thus the requirement of the frequent anthelmintic treatments. The efficiency of control can be increased through objective and accurate identification of genetically tolerant individuals by natural and artificial infections with GINs. Complete resistance is the ultimate solution, but this has generally been ignored as a commercial reality. This paper reviews the published reports on natural resistance in small ruminants and discusses the prospects of developing small ruminants, which could be resistant to GINs.

Allelic variation of the ovine Toll-like receptor 4 gene

The family of Toll-like receptors (TLRs) is responsible for recognition of pathogen-associated molecular patterns (PAMPs), and Toll-like receptor 4 (TLR4) recognizes not only exogenous ligands such as the lipopolysaccharide (LPS) of Gram-negative bacteria, but also a number of endogenous ligands. Variation in the nucleotide sequence of the ovine TLR4 gene was investigated by amplification of a fragment containing a putative ligand-binding region using polymerase chain reaction (PCR), followed by single-strand conformational polymorphism (PCR-SSCP) analysis and DNA sequencing. Four novel SSCP patterns, representing four different sequences, were identified. Either one or two different sequences were detected in individual sheep and all the sequences identified shared high homology to the TLR4 sequences from a variety of species, suggesting that these sequences represent allelic variants of the ovine TLR4 gene. Fourteen single nucleotide polymorphisms (SNPs) were detected, and 79% (11 of 14) of SNPs were non-synonymous substitutions that would result in amino acid changes. Variation detected here might have an impact on pattern recognition and hence affect the immune response to pathogens.

Identification of allelic polymorphism in the caprine IGHA gene

Variation in the immunoglobulin heavy alpha chain (IGHA) constant region has been reported in a number of species. In this study, the IGHA gene was investigated in goats using PCR-single-strand conformational polymorphism (SSCP) analysis and DNA sequencing. Three novel sequences were identified from 111 Boer and Angora goats. Either one or two sequences were detected in individual goats, and all the sequences shared high homology to the published ovine and bovine IGHA sequences. These sequences were predicted to encode three amino acid sequences, two with a longer hinge region and one with a shorter hinge region. The variation reported here may affect the structure of the hinge and hence the function of IgA.