Magda Vieira Benavides

Association between microsatellite markers of sheep chromosome 5 and faecal egg counts

Abstract This study analyses the associations between alleles at seven microsatellite markers located at the sheep chromosome 5—where the interleukin IL-3, IL-4 and IL-5 genes were mapped—and faecal egg counts (FEC) in two different flocks. The associations were analysed by estimating the average excess of alleles at each microsatellite marker on FEC. Three of the studied markers (CSRD2138, OarAE129 and TGLA176) showed significant associations with FEC in the Corriedale flock. Seven alleles at these microsatellite loci were associated with FEC and their effects ranged from −28 to +20%, relative to the FEC population mean. On the other hand, four alleles at CSRD2138 and TGLA176 microsatellite markers had significant associations with FEC in the Polwarth mob, with effects varying from −22 to −5%, relative to the FEC population mean. All microsatellites investigated presented high diversity in both flocks. Some alleles were breed specific. The CSRD2138 ∗ A allele was the only marker associated with consistent reductions in FEC for both breeds. These results indicate that markers or genes nearby the interleukin genes, such as the CSRD2138, might enhance host resistance to internal parasites in sheep by probably increasing effector cells and antibody responses.

Identification of novel loci associated with gastrointestinal parasite resistance in a Red Maasai x Dorper backcross population.

Gastrointestinal (GI) parasitic infection is the main health constraint for small ruminant production, causing loss of weight and/or death. Red Maasai sheep have adapted to a tropical environment where extreme parasite exposure is a constant, especially with highly pathogenic Haemonchus contortus. This breed has been reported to be resistant to gastrointestinal parasite infection, hence it is considered an invaluable resource to study associations between host genetics and resistance. The aim of this study was to identify polymorphisms strongly associated with host resistance in a double backcross population derived from Red Maasai and Dorper sheep using a SNP-based GWAS analysis. The animals that were genotyped represented the most resistant and susceptible individuals based on the tails of phenotypic distribution (10% each) for average faecal egg counts (AVFEC). AVFEC, packed cell volume (AVPCV), and live weight (AVLWT) were adjusted for fixed effects and co-variables, and an association analysis was run using EMMAX. Revised significance levels were calculated using 100,000 permutation tests. The top five significant SNP markers with - log10 p-values >3.794 were observed on five different chromosomes for AVFEC, and BLUPPf90/PostGSf90 results confirmed EMMAX significant regions for this trait. One of these regions included a cluster of significant SNP on chromosome (Chr) 6 not in linkage disequilibrium to each other. This genomic location contains annotated genes involved in cytokine signalling, haemostasis and mucus biosynthesis. Only one association detected on Chr 7 was significant for both AVPCV and AVLWT. The results generated here reveal candidate immune variants for genes involved in differential response to infection and provide additional SNP marker information that has potential to aid selection of resistance to gastrointestinal parasites in sheep of a similar genetic background to the double backcross population.

Galectins and collectinis expression are increased in Haemonchus contortus-infected corriedale sheep.

Galectins and collectins are proteins classified in the lectin family that have the ability to recognize molecular patterns associated with pathogens. Studies on cattle have demonstrated high expression of these proteins during infection with gastrointestinal nematodes. The aim of this study was to investigate whether the level of Haemonchus contortus infection would alter the expression of galectins (Gal11 and Gal14) and collectins (SPA and CGN) in sheep. Twelve Corriedale sheep exposed to natural infection with nematodes were divided into two groups: group 1 (G1, n = 7) and group 2 (G2, n = 5), with low and high parasite burdens, respectively, based on fecal egg counts and abomasal parasite counts. The fecal egg counts and abomasal parasite counts were significantly different (p < 0.05) between the groups. Galectin and collectin gene expression was observed in all sheep abomasal samples. However, animals with lower infection levels showed lower expression of the genes Gal14, SPA and CGN (p < 0.05). Expression of lectins was associated with the abomasal H. contortus burden, thus suggesting that these proteins may have a role in controlling of this infection.

Maternal inheritance on reproductive traits in Brangus-Ibagé cattle

Cytoplasmic inheritance influence on reproductive traits was investigated in the Brangus-Ibage cattle (3/8 Nelore x 5/8 Aberdeen Angus). Additive genetic effects were responsible for 12% ± 11% of phenotypic variation observed in first calving interval, but their contribution dropped to zero when all calving intervals (CI) were considered. The heritability estimate for age at first calving (AFC, in days) was 0.19 ± 0.09. Mitochondrial lineage (MIT) had negligible effects on phenotypic variances of calving interval (0.0 ± 0.02), calf birth weight (0.0 ± 0.01), and cow weight at calving (0.0 ± 0.01). However, for the age at first calving, MIT accounted for 0.15 ± 0.07 of total variation. Cow weight at calving had a significant linear effect on CI and AFC. Three D-loop mtDNA mutations significantly affected either calving interval (T®C at sites 16,113 and 16,119) or calf birth weight (T®C at site 16,113). The C variants had decreased CI (29 and 32 days, respectively) and increased calf weight (0.6kg). Although the effects were small, direct selection for these mutation-carrier cows might improve the reproductive and developmental performance in this herd.

Can Haemonchus placei-primary infected naïve lambs withstand Haemonchus contortus infections?

An experiment was conducted with the objective of evaluating whether a 5000 L3 larvae Haemonchus placei primary infection, a less pathogenic parasite species for sheep, could attenuate highly pathogenic Haemonchus contortus infections in lambs. Thirty nine 6-month-old lambs were divided in three primary-infection groups: (HcPI) H. contortus-primary infected lambs, (HpPI) H. placei-primary infected lambs, and (CTRL) non-infected control lambs. Later, these same individuals, then aged 10-month old, were cross challenged with Haemonchus parasite species, creating four groups: HcPI challenged with H. placei (HcPI-HpCH), HpPI challenged with H. contortus (HpPI-HcCH), HcPI challenged with H. contortus (HcPI-HcCH), and CTRL. After a 60-day challenge period, all animals were necropsied for gastrointestinal worm counts. HcPI faecal egg count average was found to be twice the HpPI FEC group (p<0.0001). The HcPI also showed lower packed cell volume averages compared to the other groups (p<0.0001). Both H. contortus- and H. placei-primary infections displayed immune responses with similar IgG levels. For the challenge trial, the larval doses used were not enough to trigger clinic infection signs in all treated groups, compared to controls, and H. placei primary infection was not able to maintain anti-H. contortus IgG levels in a subsequent H. contortus infection.

PCR-based genotyping of SNP markers in sheep.

Single nucleotide polymorphisms (SNPs) are the main type of variation in genome, enabling them to be associated with traits of economic importance in livestock. Genome-wide association studies (GWAS) have led to the discovery of SNPs associated with desirable traits in sheep. However, in these studies, SNPs are genotyped by high-throughput methods in genome scale, which are expensive and require sophisticated equipment and analysis methods. Therefore, the goal of this study was to develop a reliable, rapid, and inexpensive polymerase chain reaction (PCR)-based method to genotype a medium number of animals for a few candidate SNPs previously associated with desirable phenotypes in sheep by GWAS, using markers associated with gastrointestinal nematode resistance as a model. DNA extracted from white-blood cells of 150 sheep was submitted to PCR amplification followed by agarose gel electrophoresis and determination of banding pattern. Tetra-primer ARMS-PCR was successfully optimized after changes in annealing temperature; annealing and extension times; concentration of MgCl2 and DNA; ratios of inner, outer, forward and reverse primer; and addition of adjuvants, for genotyping the OAR2_14765360, OAR6_81718546, OAR11_62887032, and OAR12_69606944 SNPs in sheep. An extensive optimization of tetra-primer ARMS-PCR resulted in a suitable, simple, cost-effective PCR-based method of genotyping four SNP markers previously detected by chip arrays.

EFEITO DA METODOLOGIA DE ANÁLISE DA SUARDA NAS CARACTERÍSTICAS DO SUOR, PORCENTAGEM DE CERA E COR DA LÃ LAVADA (Y-Z)

Wool samples from various fleeces regions of Polwarth and Corriedale hogget ewes were analysed following two different sequences in order to record wax and suint percents, suint colour and pH and scoured wool colour. In the first method, the wax was extracted before the suint (Wax + Suint) and the second extracted suint before wax (Suint + Wax). The wax percent was greater to Wax + Suint method (P 0.05) into a smaller yellowness index (Y-Z). The correlations between characteristics within methods recorded medium values.