Sheep & Goats

Genetic architecture of somatic cell count in Sarda dairy sheep inferred from genomic information

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Abstract

Abstract Text: Somatic Cell Count (SCC) and traits describing its variability throughout lactation have been widely discussed as potential selection criteria for improving resistance to subclinical mastitis in dairy sheep. In this context, the present study investigates the genetic architecture of SCC in a nucleus flock that represents the core of the reference population for future genomic selection programs in the Sarda breed. The experimental population consisted of 5,261 Sarda ewes, reared under homogeneous management and feeding conditions. Individual milk samples were collected fortnightly from both morning and evening milkings over the period 2000-2024, resulting in a total of 145,765 SCC records. All animals and 385 ancestors were genotyped with the OvineSNP50 BeadChip. Only lactations with at least two test-day records were retained for analysis. SCC values were log-transformed into somatic cell scores (SCS: log2(SCC/100,000) + 3). Four lactation-level traits were analysed (16,554 records): average SCS (SCSav), within-lactation SCS standard deviation (SCSsd), within-lactation maximum SCS (SCSmx), and the within-lactation average deviation of SCS from the minimum value (SCSwd). A multitrait linear animal model implemented in BLUPF90, using the genomic relationship matrix, was applied to estimate heritability (h2) and genetic correlations. The model included additive genetic and permanent environmental random effects, as well as fixed effects comprising the interactions between year of production and management group, and between age class and month at lambing class. The average of individual deviations, corresponding to the sum of the genetic and non-genetic random effects of the previous model, was used as the dependent variable in a linkage disequilibrium-linkage analysis (LDLA) aimed at QTL detection. The average and standard deviation SCC value was 636 ± 1,143 x 103 cells/mL. All the SCS traits showed substantial variability, with coefficients of variation ranging from 33% to 59%. Estimates of h2 ranged from 0.26 for SCSav to 0.06 for SCSsd. Genetic correlations between SCS traits were all positive and moderate to high (0.44-0.96). Genome-wide LDLA revealed 21 SNP associations exceeding the 0.05 genome-wide significance threshold (−log10P = 6). The strongest signals were detected on OAR3 for SCSav with a peak at 18.5 Mb (−log10P = 11.70) and on OAR21 for both SCSmx and SCSwd with a peak at 13.1 Mb (−log10P = 6.12 and 6.09). Together with reliable h2 estimates and several significant genomic positions, the results support the development of genomic indexes combining polygenic and specific effects, enabling the use of this nucleus flock as a reference population for genomic selection in connected commercial herds.

Keywords: 2026

How to Cite:

Salaris, S., Usai, M., Mulas, G. & Carta, A., (2026) “Genetic architecture of somatic cell count in Sarda dairy sheep inferred from genomic information”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2283852. doi: https://doi.org/10.31274/wcgalp.23526

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