Longevity of ewes in Norwegian sheep production: descriptive study of breeds and genetic analysis of Norwegian White sheep
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- Master’s theses (BioVit) 
Longevity in breeding ewes is a complex trait affected by many factors both genetic and environmental. From an economic, environmental, and animal welfare perspective it is favourable to increase longevity. Norway has many breeds with distinctive differences, but the dominating production breed is the Norwegian White sheep (NWS). The two goals of this thesis are to first look at differences in longevity between breeds and, second, to da a genetic analysis of the longevity of Norwegian White sheep using data collected from Sauekontrollen: can longevity in NWS ewes be selected for. Two different datasets were generated, one for the breed comparisons and one for the genetic analysis. The breed comparison dataset included information about nine breeds from all of Norway between 2001 and 2022 and had mean ages between 2.7 and 3.1 years. Thegenetic analysis dataset with NWS had information from sheep farm municipalities in Viken county between 2001 and 2022.The different breeds showed quite similar longevity despite some breeds being more of a modern high-producing breed, while others were more traditional breeds. No clear patterns or change of mortality rate over the years. The five models used for the genetic analysis was based on a sire model which was expanded into including the permanent environmental effect of the dam and the maternal genetic effect of the dam. The most complex model show heritability’s estimates around 0.055 ± 0.008 on single year and 0.141 ± 0.020 for the average lifetime of the ewe, but resultswere similar for all models. Introducing longevity into a Norwegian sheep breeding scheme could be a low-cost implementation since the data is already available and the heritability is on par with growth traits.