Early detection of Haemonchus contortus infection in sheep using three different faecal occult blood tests

Haemonchus contortus is a blood-sucking parasite causing the presence of faecal occult blood (FOB). The objective was to study three different FOB tests in order to have a new indicator of H. contortus infection in sheep that could be included in the genetic evaluation system as an alternative selection criterion to faecal worm egg count (FEC). A total of 29 Corriedale lambs were experimentally infected with 10.000 larvae of H. contortus. Stool samples were recorded for FEC and FOB tests (Hexagon, Hematest® and Multistix®), blood for packed cell volume (PCV), haemoglobin, white and red blood cell count (RBC), and FAMACHA© for scoring anaemia. At the end of the experiment lambs were slaughtered to worm burden count. Field infection was achieved in 309 Merino lambs under natural parasite challenge. FEC data were normalized through logarithmic transformation (LnFEC). Pearson correlation was estimated to examine the relationship between all traits. The three tests were able to detect the presence of FOB at day 11. FEC, PCV and RBC decreased to sub-normal values from day 18. FAMACHA© score 3 was considered to be indicative of anaemia. Most of the correlations were of high magnitude, with the exception of Multistix® test that was moderately correlated with haematological parameters, LnFEC and FEC. In field infection, most samples were negative to FOB tests and the correlations were lower than those calculated under experimental infection. In conclusion, FOB tests were able to detect haemonchosis earlier than FEC under high experimental parasite challenge. However, they were not able to detect FOB under natural mixed parasite challenge. FAMACHA© and PCV demonstrated to be good indicators of Haemonchosis, having moderate to high correlations with FEC.Keywords: Faecal occult blood test, Faecal worm egg count, Haemonchosis, Sheep

Exclusion of paternity based on a panel of 89 SNP markers in a sample of Corriedale and Merino sheep from Uruguay

Se estudió el desempeño de un panel de 89 marcadores del tipo polimorfismos de un solo nucleótido (SNP) para la exclusión de paternidad en poblaciones de ovinos Corriedale y Merino del Uruguay. El valor de la menor frecuencia alélica (MAF) de los marcadores varió entre 0.05 y 0.5 en la raza Corriedale y 0.08 y 0.5 para Merino. Se lograron valores altos de probabilidad de exclusión (0.9999) de ambos padres y con un padre conocido usando menos de 50 marcadores. Cuando se cuenta solamente con un posible genotipo paterno y sin información de la madre, que es el caso más común de exclusión de paternidad, se alcanzó un valor de 0.9999 de probabilidad, utilizando la totalidad de marcadores del panel en los animales Merino pero sólo fue posible llegar a 0.9998 en la raza Corriedale. Estos resultados sugieren que el panel puede resultar de utilidad en las poblaciones Corriedale y Merino. Sin embargo, en casos específicos de poblaciones muy emparentadas (situación frecuente en cabañas) puede ser insuficiente, razón por la cual se propone el desarrollo de un panel de SNP para excluir paternidades en situaciones más complejas.Agencia Nacional de Investigación e Innovació

Herramientas moleculares para la mejora genética en ovinos

Es indudable el afianzamiento de las evaluaciones genéticas (EG) poblacionales de ovinos en el Uruguay. En la última década se ha observado un crecimiento exponencial de las mismas, evaluándose en la actualidad más de 85 cabañas y 25.000 animales al año pertenecientes a 12 razas, publicándose Diferencias Esperada en la Progenie (DEP

A comprehensive analysis of the genetic diversity and environmental adaptability in worldwide Merino and Merino-derived sheep breeds

BACKGROUND: To enhance and extend the knowledge about the global historical and phylogenetic relationships between Merino and Merino-derived breeds, 19 populations were genotyped with the OvineSNP50 BeadChip specifically for this study, while an additional 23 populations from the publicly available genotypes were retrieved. Three complementary statistical tests, Rsb (extended haplotype homozygosity between-populations), XP-EHH (cross-population extended haplotype homozygosity), and runs of homozygosity (ROH) islands were applied to identify genomic variants with potential impact on the adaptability of Merino genetic type in two contrasting climate zones. RESULTS: The results indicate that a large part of the Merino's genetic relatedness and admixture patterns are explained by their genetic background and/or geographic origin, followed by local admixture. Multi-dimensional scaling, Neighbor-Net, Admixture, and TREEMIX analyses consistently provided evidence of the role of Australian, Rambouillet and German strains in the extensive gene introgression into the other Merino and Merino-derived breeds. The close relationship between Iberian Merinos and other South-western European breeds is consistent with the Iberian origin of the Merino genetic type, with traces from previous contributions of other Mediterranean stocks. Using Rsb and XP-EHH approaches, signatures of selection were detected spanning four genomic regions located on Ovis aries chromosomes (OAR) 1, 6 and 16, whereas two genomic regions on OAR6, that partially overlapped with the previous ones, were highlighted by ROH islands. Overall, the three approaches identified 106 candidate genes putatively under selection. Among them, genes related to immune response were identified via the gene interaction network. In addition, several candidate genes were found, such as LEKR1, LCORL, GHR, RBPJ, BMPR1B, PPARGC1A, and PRKAA1, related to morphological, growth and reproductive traits, adaptive thermogenesis, and hypoxia responses. CONCLUSIONS: To the best of our knowledge, this is the first comprehensive dataset that includes most of the Merino and Merino-derived sheep breeds raised in different regions of the world. The results provide an in-depth picture of the genetic makeup of the current Merino and Merino-derived breeds, highlighting the possible selection pressures associated with the combined effect of anthropic and environmental factors. The study underlines the importance of Merino genetic types as invaluable resources of possible adaptive diversity in the context of the occurring climate changes

Cómo aumentar la resistencia genética a parásitos gastrointestinales en ovinos?. La estrategia de Uruguay. [Resumen]

Los parásitos gastrointestinales (PGI) generan mundialmente numerosas pérdidas productivas y económicas en la producción ovina, no escapando Uruguay a esta problemática. Es por esta razón que los productores comerciales y cabañeros (vendedores de genética) sitúan a la resistencia genética a PGI como una de las características prioritarias que debería tenerse en cuenta en las evaluaciones genéticas que realizan el Secretariado Uruguayo de la Lana (SUL) y el INIA

Modelación de la curva del recuento de huevos de parásitos durante el período del periparto en ovinos Merino uruguayo

Disease caused by gastrointestinal nematodes (GIN) is one of the main constraints for sheep production worldwide. Although adult categories are more resistant to GIN, a temporary loss of acquired immunity is presented around parturition, which results in the so-called “periparturient rise” (PPR) in fecal excretion of GIN eggs. The objective of the present work was to study the dynamic of the PPR and to model the faecal worm egg count (FEC) curve during the periparturient period in Uruguayan Merino sheep. Faecal samples were collected from lambing ewes during 2009 and 2010 parturitions. FEC and infective larvae cultures of each sampling were recorded. A total of 2121 records from 748 ewes, the progeny of 107 sires, were used in the statistical analysis. FEC data were normalized using two logarithmic transformations: Log FEC= Loge (FEC+100) and Log FEC_st (Log FEC with the variance standardized within contemporary group). Three functions were compared to shape the PPR curve. Haemonchus spp. was the most prevalent parasite. Log FEC_st was the selected response variable of the model, for its better adjustment to a normal distribution and a more homogeneous residual variance. The fixed regression model with Legendre polynomials was the selected one, based on the selection model criteria (Akaike & Schwarz Bayesian Information Criteria). The highest egg output was observed between two and four weeks post-lambing. In conclusion, the PPR observed in Uruguayan Merino lambing ewes had the maximum egg output matched with the milk production peak.La infección por nematodos gastrointestinales (GIN) es una de las principales limitantes de la producción ovina mundial. Si bien los adultos son más resistentes a los GIN, una pérdida temporal de la inmunidad adquirida se presenta en el período del periparto, resultando en el “alza de lactación” (PPR) en la eliminación de huevos de GIN (HPG). El objetivo del presente trabajo fue estudiar la dinámica del PPR y obtener la curva del recuento del HPG durante el periparto en ovejas Merino uruguayo. Se recogieron muestras de heces de ovejas en las pariciones 2009 y 2010, realizándose HPG y coprocultivo de cada muestreo. Para el análisis estadístico se utilizaron 2121 datos de 748 ovejas, hijas de 107 padres. Se llevaron a cabo dos transformaciones logarítmicas de manera que los datos siguieran una distribución normal: Log HPG= Loge (HPG+100) y Log HPG_st (Log HPG con la varianza normalizada dentro del grupo contemporáneo). Se compararon tres funciones para modelar la curva del PPR. Haemonchus spp. fue el género más frecuente. Log HPG_st fue la variable de respuesta del modelo seleccionada, por el mejor ajuste a la distribución normal y mayor homogeneidad de la varianza residual. Se seleccionó el modelo con polinomios de Legendre, en base a los criterios de selección del modelo (Akaike y Schwarz Bayesian Information Criteria). La mayor eliminación de huevos se observó entre las dos y cuatro semanas posparto. En conclusión, se observó el PPR en ovejas Merino uruguayo, coincidiendo la máxima eliminación de huevos de GIN con el pico máximo de producción de leche

Genetic parameters for body weight, worm resistance, packed cell volume and FAMACHA@ under natural infection in Corriedale sheep.

ABSTRACT.Gastrointestinal parasites (GIP) are one of the main constraint for sheep production worldwide. In Uruguay, the most prevalent and pathogenic parasite is Haemonchus contortus. One approach to control parasite infection is to select genetically resistant animals into a sheep-breeding program. Faecal egg count (FEC) is the criterion most used to evaluate genetic resistance to GIP, although there are alternative indicators that could be used. The aim of the present study was to estimate genetic parameters for body weight, FEC, packed cell volume (PCV) and FAMACHA© score, to determine the possibility to include these traits in the genetic evaluation of GIP resistance, as complementary selection criteria to FEC. Data from 15,073 post-weaned lambs, the offspring of 343 rams, were recorded during a 16-year period from 2000 to 2015, from Uruguayan Corriedale stud flocks. A Bayesian analysis was performed to estimate genetic parameters, using a multivariate animal model including post-weaning body weight (BW), FEC, PCV and FAMACHA©. Heritabilities for these traits were of low to moderate magnitude (0.14 to 0.35). Genetic correlation (rg) was close to zero for FAMACHA©-BW, low but favourable for FEC-BW (-0.12) and FEC-PCV (-0.23), and moderate to high between PCV-BW, PCV-FAMACHA© and FEC-FAMACHA© (0.54-0.73). The high rg between FEC-FAMACHA© estimated in the present study, indicate the possibility to complement both traits in order to select resistant and resilient animal to GIP. There would be an improvement not only at a genetic level but also for the environment and it would help to lead with the problematic situation of anthelmintic resistance. Keywords: Haemonchus contortus, faecal egg count, heritability, genetic correlation

SNP genotyping for parentage identification in a Merino nucleus and in a commercial Highlander flock.

ABSTRACT.Pedigree information is required to estimate breeding values accurately and to ensure high rates of genetic gain. DNA markers information can be used as an alternative to traditional recording of pedigree, being SNPs the markers of choice for parentage verification. The aim of the present study was to determine sheep parentage by SNPs using a very low density panel in: 1) a stud Merino flock to know the percentage of parentage error in order to correct pedigree misidentification and; 2) a commercial Highlander flock, to study the possibility to not control lambing anymore because for the breeder it is very laborious, time-consuming and disturb the relationship ewe-lambs during parturition. Genomic DNA was isolated from 200 samples of Merino sheep in 2015 and from 108 and 904 samples of Merino and Highlander sheep in 2016, respectively; and were genotyped with a very low density panel containing 507 SNPs. In 2015, for the 91 lambs genotyped, the error in parentage assignment was 16.5%. Although the assigned sire did not match with the declared sire for 15 lambs, the true sire was assigned for 14 of them. Thus, 99% of the lambs genotyped, had a sire assigned by the SNP panel. For the 80 lambs with their dams genotyped, the error rate was 12.5%. For the 10 lambs with mismatches with the declared dams, the true dam was assigned for five of them. In 2016, Merino samples were genotyped to link only lambs with their sires. For the 101 lambs, the error of parentage assignment was 21.8%. For Highlander, 7.5% of samples failed the genotyping and analyses was conducted without knowledge of the relationships between lambs with sires and dams. The 51% of the lambs genotyped had a sire and a dam assigned, 21% had only the sire assigned and 15% had only assigned a dam. Thus, genotyping by SNPs assigned a sire to the 72% of the lambs and a dam to the 66% of the lambs. The main problem was that only 5 of the 11 rams used as sires were genotyped and the high percentage of samples which failed the genotyping. However, taking into account the lack of information related to pedigree, we consider that a high rate of lambs had a sire and a dam assigned by the SNP panel. In conclusion, the development of a SNP panel for parentage assignment at a low price, would provide breeders with the opportunity of making mating management and control lambing easier and more relaxed while improving the known of pedigree information, ensuring high rates of genetic gain. Keywords: molecular markers, parentage exclusion, parentage verification, sheep

Ganadería vacuna y ovina: más de 200 artículos testigos del desarrollo de la investigación.

Gran parte de lo publicado refiere a tecnologías de procesos, manejos coyunturales o herramientas tecnológicas validadas