R.F. Veerkamp and Y. de Haas (eds) Proceedings of 12 th World Congress on Genetics Applied to Livestock Production (WCGALP) 3028 DOI: 10.3920/978-90-8686-940-4_735, © S. Salaris et al. 2022 735. Options for the selective breeding for resistance to gastro-intestinal nematodes of Sarda breed sheep S. Salaris 1* , S. Casu 1 , M.G. Usai 1 , A. Scala 2 and A. Carta 1 1 Research Unit: Genetics and biotechnology, AGRIS Sardegna, 07040 Olmedo, Italy; 2 Department of Veterinary Medicine, University of Sassari, 07100 Sassari, Italy; slsalaris@agrisricerca.it Abstract In this paper we summarize results of previous studies on the resistance to gastro-intestinal nematodes obtained in a nucleus of Sarda ewes in terms of heritability estimate, QTL detection, functional annotation, association analysis based on imputed sequence data and prediction of GEBV for male selection candidates of the Herd Book. Heritability of log-transformed faecal egg counts was 0.21±0.015. Ten QTL regions were defned on nine chromosomes with an LDLA approach. In the most signifcant QTL regions, we identifed functional candidate genes that contain high or moderate impact polymorphisms. Te expected accuracies of GEBV are related to the amount of relationships with the nucleus. Te Sarda breeders are assessing the feasibility of a selection program for nematode resistance based on fecal egg counting and on the genotypes in the nucleus fock and of selection candidate males bred in Herd Book farms genetically connected with the experimental fock. Introduction Gastrointestinal nematodes (GIN) are a major health problem in grazing animals that causes important yield reductions and increased production costs due to medical treatments and higher culling rates (Mavrot et al., 2015). Fecal egg count (FEC), i.e. the number of parasite eggs per gram of faeces has been largely used as proxy trait to measure resistance to GIN. In Sardinia, sheep farming systems are based on grazing natural pastures and forage crops where GIN infection is unavoidable. Tus, most farmers administrate anti-helminthics ofen with an empirical approach in terms of individual diagnosis, doses and frequency of treatments (Sechi et al., 2010). Genetic variation between individuals and breeds has been documented (Aguerre et al., 2018). However, the inclusion of GIN resistance in current breeding scheme is difcult due to the laboriousness of the FEC recording at Herd Book (HB) scale. For the Sarda breed, it is available a female nucleus in an experimental farm in which the ewes generated by HB rams, have been pedigree recorded, genotyped and repeatedly measured for FEC for twenty years. Te genetic links of these animals with those of the HB make it possible to use their data to study the genetic determinism of resistance to GIN at breed level. In this paper, we summarize the results obtained in previous studies on this experimental population in terms of heritability estimate, QTL detection, functional annotation, association analysis based on imputed sequence data (Casu et al., 2022) and prediction of GEBV for male selection candidates of the HB (Salaris et al., 2021). Results will be discussed focusing on the feasibility of genetic improvement strategies based on genomic tools. Materials & methods Experimental population. Te nucleus fock (FRP) was set in 1999 with the frst generation of ewes consisting in 928 back-cross Lacaune × Sarda. Te following generations were obtained by mating adult ewes with rams coming from the artifcial insemination center of the HB. In total, 5,386 ewes from 218 rams (10 F1 and 208 Sarda) were generated until 2020. Te farming system was similar to that commonly applied in Sardinia with most of the adult ewes lambing in autumn and yearlings lambing between January and March. Te feeding regime was based on grazing of natural pastures and forage crops, supplemented by hay and concentrates in winter and late spring. From 2000 to 2020 individual FEC were recorded from 1 to 3 times per year on adult ewes, more frequently in September and July. Afer editing, 16,530 records from https://www.wageningenacademic.com/doi/pdf/10.3920/978-90-8686-940-4_735 - Saturday, February 11, 2023 4:03:19 PM - IP Address:3.88.231.18