Genetic characterization of resistance to Haemonchus contortus in Morada Nova sheep
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Data
2020-05-05
Autores
Haehling, Marei Borsch von
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Universidade Estadual Paulista (Unesp)
Resumo
Nematódeos gastrintestinais são um grande obstáculo na produção de ovinos. A seleção para resistência tem sido uma abordagem eficiente e factível para lidar com esse problema. A utilização e investigação de marcadores genéticos para características de resistência poderiam acelerar o melhoramento genético e levar ao melhor entendimento dos mecanismos moleculares de resistência. O objetivo desse estudo foi verificar a possibilidade de seleção para características de resistência e resiliência em cordeiros da raça Morada Nova, estimar as potenciais respostas correlacionadas e avaliar se cinco polimorfismos de base única (SNPs, OAR2_14765360, OAR6_81718546, OAR11_62887032, OAR12_69606944 and OAR15_59871543) estão associados às características de resistência e resiliência. Um total de 287 cordeiros e 131 matrizes foram submetidas a dois desafios parasitários consecutivos e independentes por infecção oral com 4.000 larvas infectantes (L3) de Haemonchus contortus. Contagem de ovos por grama de fezes (OPG), volume globular (VG) e peso corporal vivo (PV) foram monitorados a cada uma ou duas semanas para 42 dias em cada desafio. Amostras de DNA de 287 cordeiros, 131 matrizes e 4 reprodutores machos foram amplificados por ARMS-PCR ou PCR-RFLP e os genótipos foram determinados. Estimativas de parâmetros genéticos foram obtidas para dias individuais de coleta, e para a característica como um todo com medidas repetidas, utilizando modelos animais mistos. A análise de variância (ANOVA) foi utilizada para análises de associação entre genótipos dos SNPs e fenótipos. No caso de associação significativa, o efeito de substituição de alelo foi calculado baseado em um modelo linear. As estimativas de herdabilidade para OPG no primeiro e segundo desafio parasitário foram, respectivamente, 0,25 ± 0,18 e 0,46 ± 0,19 para cordeiros, e 0,00 ± 0,09 e 0,20 ± 0,16 para matrizes. Para VG, as estimativas de herdabilidade foram 0,23 ± 0,14 e 0,32 ± 0,16 para cordeiros e 0.13 ± 0.11 e 0.37 ± 0.18 para matrizes. A estimativa de herdabilidade do ganho de peso diário (GPD) total foi 0,70 ± 0,21. As correlações genéticas de OPG e VG entre cordeiros e matrizes foram 0,36 ± 0,08 e 0,42 ± 0,08, respectivamente. Não foi encontrada correlação genética significativa entre GPD e as demais características, enquanto ocorreu uma correlação genética negativa entre OPG e VG (-0.70 ± 0.03). OAR2_14765360 e OAR12_69606944 foram associados com OPG, e OAR12_69606944 também teve um efeito significativo no VG e GPD, mostrando associação favorável do genótipo CC com todas as características avaliadas. OAR6_81718546 e OAR11_62887032 foram associados ao GPD, e OAR6_81718546 teve um efeito adicional no VG. OAR15_59871543 não foi polimórfico na população. OAR6_81718546 e OAR12_69606944 apresentaram efeito de substituição de alelo significativo de -1.06 ± 0.52 kg para o alelo T no PV final e 0.74 ± 0.32 para o alelo C no VG do mesmo dia de desafio, respectivamente. A seleção para OPG baixo e VG alto é possível em cordeiros da raça Morada Nova. A seleção para OPG baixo deve ter uma resposta correlacionada no VG (levando a VG mais alto), enquanto não é esperada uma resposta correlacionada no GPD. A seleção para OPG baixo e VG alto em cordeiros deve levar a OPG baixo e VG alto em matrizes. Um índice contendo GPD total e dados de duas coletas de OPG e VG (conduzidas 4 a 6 semanas após a infecção durante o segundo desafio parasitário) pode ser utilizado como critério de seleção em cordeiros, permitindo seleção simultânea para OPG mais baixo, VG mais elevado e GPD mais elevado. Nossos resultados suportam a existência de locos de características quantitativas (QTL) para resistência e resiliência em desequilíbrio de ligação com os SNPs polimórficos e sugere o seu uso futuro para a exploração dessas características em ovinos Morada Nova.
Gastrointestinal nematodes are a major constraint in sheep production. Breeding for resistance has proven to be an effective and feasible approach to address this problem. The use and investigation of genetic markers for resistance traits could accelerate genetic progress and lead to a better understanding of underlying molecular mechanisms. The aim of this study was to verify the possibility of selection for resistance and resilience traits in Morada Nova lambs, to estimate potential correlated responses and to evaluate if five single nucleotide polymorphisms (SNPs) (OAR2_14765360, OAR6_81718546, OAR11_62887032, OAR12_69606944 and OAR15_59871543) are associated with resistance and resilience traits. A total of 287 lambs and 131 ewes were submitted to two consecutive independent parasite challenges by oral infection with 4,000 infective larvae (L3) of Haemonchus contortus. Faecal egg counts (FEC), packed cell volume (PVC) and body weight were measured every one or two weeks for 42 days in each trial. DNA samples from 287 lambs, 131 ewes and 4 rams were amplified by ARMS-PCR or PCR-RFLP and genotypes were determined. Estimates of genetic parameters were obtained for individual records as well as for overall traits with repeated measures, using mixed animal models. Analysis of variance (ANOVA) was used for association analyses between SNP genotypes and phenotypes. In case of significant association, the allele substitution effect was calculated based on a linear model. Heritability estimates of FEC in the first and second parasite challenge were, respectively, 0.25 ± 0.18 and 0.46 ± 0.19 for lambs, and 0.00 ± 0.09 and 0.20 ± 0.16 for ewes. For PCV, heritability estimates were 0.23 ± 0.14 and 0.32 ± 0.16 for lambs and 0.13 ± 0.11 and 0.37 ± 0.18 for ewes. The overall weight gain heritability estimate was 0.70 ± 0.21. Genetic correlations of FEC and PCV between lambs and ewes were 0.36 ± 0.08 and 0.42 ± 0.08, respectively. No significant genetic correlation was found between weight gain and the other traits, while there was a negative genetic correlation between FEC and PCV (-0.70 ± 0.03). OAR2_14765360 and OAR12_69606944 were associated with FEC, and OAR12_69606944 also had significant effects on PCV and weight gain, showing favourable associations of the CC genotype with all evaluated traits. Both OAR6_81718546 and OAR11_62887032 were associated with weight gain, and OAR6_81718546 had an additional effect on PCV. OAR15_59871543 was not polymorphic in the population. OAR6_81718546 and OAR12_69606944 presented significant allele substitution effects of -1.06 ± 0.52 kg for the T allele on final body weight and 0.74 ± 0.32 for the C allele in PCV of the same sampling date, respectively. Selection for low FEC and high PCV is possible in Morada Nova lambs. Selection for low FEC should have a correlated response on PCV (leading to higher PCV), while no correlated response is expected on weight gain. Selection for low FEC and high PCV in lambs should lead to low FEC and high PCV in ewes. An index consisting of overall weight gain and two records of FEC and PCV (taken 4 to 6 weeks after infection during the second parasite challenge) can be used as selection criterion in the Morada Nova lambs, allowing simultaneous selection for lower FEC, higher PCV and higher weight gain. Our findings support the existence of quantitative trait loci (QTL) for resistance and resilience in linkage disequilibrium with the polymorphic SNPs and suggest their future use for explorations of these traits in Morada Nova sheep. Keywords: genetic markers, genetic parameters, host resistance, resilience, parasite challenge
Gastrointestinal nematodes are a major constraint in sheep production. Breeding for resistance has proven to be an effective and feasible approach to address this problem. The use and investigation of genetic markers for resistance traits could accelerate genetic progress and lead to a better understanding of underlying molecular mechanisms. The aim of this study was to verify the possibility of selection for resistance and resilience traits in Morada Nova lambs, to estimate potential correlated responses and to evaluate if five single nucleotide polymorphisms (SNPs) (OAR2_14765360, OAR6_81718546, OAR11_62887032, OAR12_69606944 and OAR15_59871543) are associated with resistance and resilience traits. A total of 287 lambs and 131 ewes were submitted to two consecutive independent parasite challenges by oral infection with 4,000 infective larvae (L3) of Haemonchus contortus. Faecal egg counts (FEC), packed cell volume (PVC) and body weight were measured every one or two weeks for 42 days in each trial. DNA samples from 287 lambs, 131 ewes and 4 rams were amplified by ARMS-PCR or PCR-RFLP and genotypes were determined. Estimates of genetic parameters were obtained for individual records as well as for overall traits with repeated measures, using mixed animal models. Analysis of variance (ANOVA) was used for association analyses between SNP genotypes and phenotypes. In case of significant association, the allele substitution effect was calculated based on a linear model. Heritability estimates of FEC in the first and second parasite challenge were, respectively, 0.25 ± 0.18 and 0.46 ± 0.19 for lambs, and 0.00 ± 0.09 and 0.20 ± 0.16 for ewes. For PCV, heritability estimates were 0.23 ± 0.14 and 0.32 ± 0.16 for lambs and 0.13 ± 0.11 and 0.37 ± 0.18 for ewes. The overall weight gain heritability estimate was 0.70 ± 0.21. Genetic correlations of FEC and PCV between lambs and ewes were 0.36 ± 0.08 and 0.42 ± 0.08, respectively. No significant genetic correlation was found between weight gain and the other traits, while there was a negative genetic correlation between FEC and PCV (-0.70 ± 0.03). OAR2_14765360 and OAR12_69606944 were associated with FEC, and OAR12_69606944 also had significant effects on PCV and weight gain, showing favourable associations of the CC genotype with all evaluated traits. Both OAR6_81718546 and OAR11_62887032 were associated with weight gain, and OAR6_81718546 had an additional effect on PCV. OAR15_59871543 was not polymorphic in the population. OAR6_81718546 and OAR12_69606944 presented significant allele substitution effects of -1.06 ± 0.52 kg for the T allele on final body weight and 0.74 ± 0.32 for the C allele in PCV of the same sampling date, respectively. Selection for low FEC and high PCV is possible in Morada Nova lambs. Selection for low FEC should have a correlated response on PCV (leading to higher PCV), while no correlated response is expected on weight gain. Selection for low FEC and high PCV in lambs should lead to low FEC and high PCV in ewes. An index consisting of overall weight gain and two records of FEC and PCV (taken 4 to 6 weeks after infection during the second parasite challenge) can be used as selection criterion in the Morada Nova lambs, allowing simultaneous selection for lower FEC, higher PCV and higher weight gain. Our findings support the existence of quantitative trait loci (QTL) for resistance and resilience in linkage disequilibrium with the polymorphic SNPs and suggest their future use for explorations of these traits in Morada Nova sheep. Keywords: genetic markers, genetic parameters, host resistance, resilience, parasite challenge
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Palavras-chave
Genetic markers, Genetic parameters, Host resistance, Resilience, Parasite challenge, Marcadores genéticos, Parâmetros genéticos, Resistência do hospedeiro, Resiliência, Desafio parasitário