Abstract
This study reports the phenotypic trends for wool, growth, and reproductive traits in mixed-age ewes after twenty years of genetic selection. Data were obtained from the Merino nucleus flock in Uruguay between 1999 and 2020. Overall, the aim of this selection flock was to reduce the fiber diameter (FD) and increase both the clean fleece weight (CFW) and live weight (LW). Data on ewe wool traits, LW, body condition score (BCS), the total number of lambs weaned (TLW), and the total LW of lambs weaned (TWW) across all lambing opportunities (1–8 mating seasons) were analyzed. Between 1292 and 2063 ewes were measured, depending on the trait considered. Ewe FD decreased by approximately 3 µm (19–16 µm), whereas greasy fleece weight (GFW) increased by 0.2 kg. This improvement in wool traits was accompanied by increases in LW at mating (3 kg), decreases in BCS at mating (approximately by 1 unit), and a small positive change in TWW across years. This study demonstrated that increasing farmer income by selecting for finer wool, heavier fleeces, and heavier animals can be obtained without compromising ewe lifetime reproduction.
Highlights
During the 1990s, the Uruguayan wool industry processed mainly mid-micron wool (25.0–30.0 μm) [1]
A high negative genetic correlation between clean fleece weight (CFW) and the number of lambs weaned per ewe joined has been reported in superfine Merino sheep [10]. This inconsistency may be associated with the type of trait analyzed
This study demonstrated that selection programs (FMP and CRILU) applied between 1999 and 2020 in Uruguay resulted in improvements in economically relevant wool traits in mixed-age ewes
Summary
During the 1990s, the Uruguayan wool industry processed mainly mid-micron wool (25.0–30.0 μm) [1]. A high negative genetic correlation (−0.65 ± 0.14) between CFW and the number of lambs weaned per ewe joined in superfine Merino sheep suggests that selection for increased CFW could reduce reproductive performance [10]. This is consistent with a negative association between CFW and singleton lamb survival [19]. Other studies have shown that selection for increased CFW as a component of a multitrait breeding program can be achieved without compromising the reproduction rate [21,22,23] Most of these studies have been conducted in Australia and the inconsistencies in research findings may be associated with the animal genotype and nutritional conditions [10,18]. There is currently no scientific information focused on the potential effects of selection for reduced FD and increased CFW on ewe growth and reproductive traits in the Uruguayan Merino population
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