Productive and reproductive consequences after twelve years of selection for ultrafine wool production in a Merino Genetic Nucleus

This study evaluated the productive and reproductive performance of Merino sheep after twelve years of selection for ultrafine wool production in Uruguay. The breeding objective aimed to maintain low fiber diameter, while increasing both fleece weight and live weight. The research was conducted on the Merino Genetic Nucleus within the Regional Consortium of Ultrafine Wool, spanning from 2010 to 2022. Data from 4,809 lambs and 1,741 ewes were analyzed across three time periods (2010–2013, 2014–2018, and 2019–2022). The traits evaluated were fiber diameter, greasy fleece weight, staple length, clean wool yield, brightness, yellowness, live weight, body condition score, fertility, prolificacy, lamb survival, and weaning rate. Phenotypic results showed that selection effectively reduced fiber diameter while increasing fleece weight, indicating successful genetic progress. Ewes exhibited higher live weight at mating, but progeny did not show a similar trend, suggesting potential nutritional limitations. Wool quality traits (clean fleece yield, brightness, staple length) also improved over time. However, body condition score and fat thickness declined in both progeny and ewes, indicating an imbalance between increased nutritional demands and restricted access to high-quality feed. Reproductive performance remained stable, with fertility and lamb survival rates improving in the final period, likely due to enhanced management strategies. Despite concerns about potential trade-offs between wool production and reproductive efficiency, the findings indicate that a well-balanced selection approach can sustain high wool quality without compromising ewe productivity. Future research should continue addressing reproductive, health, and welfare traits alongside production and quality traits, with a focus on nutritional requirements and climate adaptation to ensure sustainable genetic progress in ultrafine wool sheep production.