Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract
Parasitosis caused by gastrointestinal nematodes (GIN) limits sheep production in pastoral systems in Uruguay. The use of anthelmintics has led to nematode resistance to drenches. Selection for resistance to GIN has proven to be beneficial. Worm egg count per gram of faeces (WEC) is used to identify resistant sheep, but there is a lack of consensus on its accuracy and the number of animals to sample. Applying statistical theory, I found that 100 WEC is accurate enough, but the sample size used is inadequate. Defining resistance to GIN as a trait in the selection objective is not straightforward. There are two options for incorporating it into flocks: within- flock selection, and incorporation of genetically improved material. I used a desired gains approach to include resistance to GIN in a multi-trait selection objective in Merino sheep. The index initially used resulted in equal importance to wool and meat, and I gradually placed greater emphasis on resistance to GIN during selection. After 10 years, with a 25 % emphasis on resistance to GIN, I predicted a WEC reduction below the threshold of 500 WEC at low and medium infestations. With high infestations, an emphasis of 50 % or more was required, which negatively affected other production traits. In such cases, within flock selection would not eliminate the need to use anthelmintics in 10 years. Difficulties specific to selection for resistance to GIN and other constraints could result in lower gains than predicted. Genetic gain could be accelerated by selecting within and between flocks, taking advantage of efforts made by national as well as overseas breeders. Foreign sources have shown resistance to GIN locally without affecting production traits. Producers should use breeding values from genetic evaluations when acquiring rams, once they have decided on the emphasis to be placed on resistance to GIN.
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Coeditada entre Facultad de Agronomía - Udelar y el Instituto Nacional de Investigación Agropecuaria (INIA)
2023
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| Online Access: | https://agrocienciauruguay.uy/index.php/agrociencia/article/view/1465 |
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Sanchez Batista, Ana Laura Ponzoni, Raul Walter |
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Sanchez Batista, Ana Laura Ponzoni, Raul Walter Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract |
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Sanchez Batista, Ana Laura Ponzoni, Raul Walter |
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Sanchez Batista, Ana Laura |
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Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract |
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Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract |
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Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract |
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Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract |
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Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract |
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studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: doctoral thesis abstract |
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Parasitosis caused by gastrointestinal nematodes (GIN) limits sheep production in pastoral systems in Uruguay. The use of anthelmintics has led to nematode resistance to drenches. Selection for resistance to GIN has proven to be beneficial. Worm egg count per gram of faeces (WEC) is used to identify resistant sheep, but there is a lack of consensus on its accuracy and the number of animals to sample. Applying statistical theory, I found that 100 WEC is accurate enough, but the sample size used is inadequate. Defining resistance to GIN as a trait in the selection objective is not straightforward. There are two options for incorporating it into flocks: within- flock selection, and incorporation of genetically improved material. I used a desired gains approach to include resistance to GIN in a multi-trait selection objective in Merino sheep. The index initially used resulted in equal importance to wool and meat, and I gradually placed greater emphasis on resistance to GIN during selection. After 10 years, with a 25 % emphasis on resistance to GIN, I predicted a WEC reduction below the threshold of 500 WEC at low and medium infestations. With high infestations, an emphasis of 50 % or more was required, which negatively affected other production traits. In such cases, within flock selection would not eliminate the need to use anthelmintics in 10 years. Difficulties specific to selection for resistance to GIN and other constraints could result in lower gains than predicted. Genetic gain could be accelerated by selecting within and between flocks, taking advantage of efforts made by national as well as overseas breeders. Foreign sources have shown resistance to GIN locally without affecting production traits. Producers should use breeding values from genetic evaluations when acquiring rams, once they have decided on the emphasis to be placed on resistance to GIN. |
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Coeditada entre Facultad de Agronomía - Udelar y el Instituto Nacional de Investigación Agropecuaria (INIA) |
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2023 |
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https://agrocienciauruguay.uy/index.php/agrociencia/article/view/1465 |
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AT sanchezbatistaanalaura studiesontheinclusionofgeneticresistancetogastrointestinalparasitesinsheepbreedingdoctoralthesisabstract AT ponzoniraulwalter studiesontheinclusionofgeneticresistancetogastrointestinalparasitesinsheepbreedingdoctoralthesisabstract AT sanchezbatistaanalaura estudiossobrelainclusionderesistenciageneticaaparasitosgastrointestinalesenlaselecciondeovinosresumendetesisdoctoral AT ponzoniraulwalter estudiossobrelainclusionderesistenciageneticaaparasitosgastrointestinalesenlaselecciondeovinosresumendetesisdoctoral |
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oai:oai.agrocienciauruguay.uy:article-14652024-03-13T11:32:08Z Studies on the inclusion of genetic resistance to gastrointestinal parasites in sheep breeding: Doctoral thesis abstract Estudios sobre la inclusión de resistencia genética a parásitos gastrointestinales en la selección de ovinos: Resumen de tesis doctoral Sanchez Batista, Ana Laura Ponzoni, Raul Walter WEC accuracy sample size desired gains approach between and within flocks selection precisión del conteo de huevos por gramo (HPG) tamaño de muestra ganancias deseadas selección intra- y entre majadas Parasitosis caused by gastrointestinal nematodes (GIN) limits sheep production in pastoral systems in Uruguay. The use of anthelmintics has led to nematode resistance to drenches. Selection for resistance to GIN has proven to be beneficial. Worm egg count per gram of faeces (WEC) is used to identify resistant sheep, but there is a lack of consensus on its accuracy and the number of animals to sample. Applying statistical theory, I found that 100 WEC is accurate enough, but the sample size used is inadequate. Defining resistance to GIN as a trait in the selection objective is not straightforward. There are two options for incorporating it into flocks: within- flock selection, and incorporation of genetically improved material. I used a desired gains approach to include resistance to GIN in a multi-trait selection objective in Merino sheep. The index initially used resulted in equal importance to wool and meat, and I gradually placed greater emphasis on resistance to GIN during selection. After 10 years, with a 25 % emphasis on resistance to GIN, I predicted a WEC reduction below the threshold of 500 WEC at low and medium infestations. With high infestations, an emphasis of 50 % or more was required, which negatively affected other production traits. In such cases, within flock selection would not eliminate the need to use anthelmintics in 10 years. Difficulties specific to selection for resistance to GIN and other constraints could result in lower gains than predicted. Genetic gain could be accelerated by selecting within and between flocks, taking advantage of efforts made by national as well as overseas breeders. Foreign sources have shown resistance to GIN locally without affecting production traits. Producers should use breeding values from genetic evaluations when acquiring rams, once they have decided on the emphasis to be placed on resistance to GIN. Las parasitosis gastrointestinales causadas por nematodos son la principal limitante sanitaria en sistemas pastoriles ovinos en Uruguay. El uso de antihelmínticos ha llevado a resistencia de los nematodos a los principios activos. La selección por resistencia a parásitos gastrointestinales (RPGI) ha demostrado ser beneficiosa. Se utiliza el conteo de huevos por gramo de materia fecal (HPG) para identificar ovinos resistentes, pero falta consenso sobre su precisión y cantidad de animales a muestrear. Aplicando teoría estadística, encontré que 100 HPG es precisión suficiente, pero el tamaño de muestra utilizado es menor que el recomendable. Definir la RPGI como rasgo en el objetivo de selección no es sencillo. Hay dos formas de incorporar la RPGI en las majadas: selección dentro de majada e incorporación de material mejorado. Utilicé un enfoque de ganancias deseadas incluyendo la RPGI en un objetivo de selección multi-carácter en Merinomerino. Inicialmente, asigné igual importancia a lana y carne, y gradualmente enfaticé más la RPGI. En las predicciones a 10 años, con un énfasis del 25 % en RPGI, HPG estuvo por debajo de 500 en infestaciones bajas y medias. Se requirió un énfasis del 50 % o más en caso de infestaciones altas, que afectó negativamente otros rasgos de producción. Con alta infestación, la selección dentro de la majada no eliminaría la necesidad de antihelmínticos en 10 años. Dificultades específicas de la selección por RPGI y otras limitantes podrían resultar en ganancias menores a las predichas. La ganancia genética podría acelerarse seleccionando dentro y entre majadas, aprovechando esfuerzos hechos por criadores nacionales y extranjeros. Las fuentes extranjeras han demostrado expresar la RPGI en nuestro país sin afectar el desempeño productivo. Los productores deberían usar los valores de cría producto de las evaluaciones genéticas en la adquisición de sus carneros una vez que hayan decidido el énfasis a poner en la RPGI. Coeditada entre Facultad de Agronomía - Udelar y el Instituto Nacional de Investigación Agropecuaria (INIA) 2023-11-09 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion application/pdf https://agrocienciauruguay.uy/index.php/agrociencia/article/view/1465 10.31285/AGRO.27.1465 Agrociencia Uruguay; Vol. 27 No. Supplement theses (2023); e1465 Agrociencia Uruguay; Vol. 27 Núm. Supplement theses (2023); e1465 Agrociencia Uruguay; v. 27 n. Supplement theses (2023); e1465 2730-5066 eng spa https://agrocienciauruguay.uy/index.php/agrociencia/article/view/1465/1701 https://agrocienciauruguay.uy/index.php/agrociencia/article/view/1465/1702 Copyright (c) 2023 Agrociencia Uruguay https://creativecommons.org/licenses/by/4.0 |