Genetic and phenotypic relationships between ewe reproductive performance and wool and growth traits in Uruguayan Ultrafine Merino sheep

Abstract

This study reports genetic parameters for yearling and adult wool and growth traits, and ewe reproductive performance. Data were sourced from an Uruguayan Merino flock involved in a long-term selection program focused on reduced fibre diameter (FD), and increased clean fleece weight (CFW) and live weight (LW). Pedigree and performance data from approximately 5,700 mixed-sex yearling lambs and 2,000 mixed-age ewes born between 1999 and 2019 were analysed. The number of records ranged from 1,267 to 5,738 for yearling traits, and from 1,931 to 7,079 for ewe productive and reproductive performance. Data on yearling and adult wool traits, LW and body condition score (BCS), yearling eye muscle area (Y_EMA), and fat thickness (Y_FAT), and several reproduction traits were analysed. The genetic relationships between FD and reproduction traits were not different from zero. Moderate unfavourable genetic correlations were found between adult CFW and ewe lifetime reproduction traits (-0.34 ± 0.08 and -0.33 ± 0.09 for total number of lambs weaned and total lamb live weight at weaning, respectively). There were moderate to strong positive genetic correlations between yearling LW and all reproduction traits other than ewe rearing ability (-0.08 ± 0.11) and pregnancy rate (0.18 ± 0.08). The genetic correlations between Y_EMA and reproduction traits were positive and ranged from 0.15 to 0.49. Moderate unfavourable genetic correlations were observed between yearling FD and Y_FAT and between adult FD and BCS at mating (0.31 ± 0.12 and 0.23 ± 0.07, respectively). The genetic correlations between adult fleece weight and ewe BCS at different stages of the cycle were negative, but generally not different from zero. This study shows that selection for reduced FD is unlikely to have any effect on reproduction traits. Selection for increased yearling LW and Y_EMA will improve ewe reproductive performance. On the other hand, selection for increased adult CFW will reduce ewe reproductive performance, whereas selection for reduced FD will negatively impact on body fat levels. Although unfavourable genetic relationships between wool traits and both FAT and ewe reproductive performance existed, simultaneous improvements in the traits would occur using appropriately designed indexes.

A genome-wide association study reveals novel SNP markers associated with resilience traits in two Mediterranean dairy sheep breeds

“…Aguerre et al (2018) have reported BCS heritability estimates of 0.25 for blond-faced Manech sheep. The present estimates were also higher compared to the ones reported for meat and wool sheep, most of which ranged from 0.04 to 0.32 (Walkom and Brown, 2017;Macé et al, 2018;Snyman and Fisher, 2019;Marques et al, 2020;Oliveira et al, 2021;Rodrigues et al, 2021;Hickey et al, 2022;Ramos et al, 2023a). However, one study reported estimates of New Zealand Merino ewes up to 0.66 depending on the reproductive stage (Tait et al, 2018).…”

Whole-Genome Resequencing Reveals Selection Signal Related to Sheep Wool Fineness

“…Thus, the metabolic processes and energy balance of adipocytes may affect the surrounding hair follicles and hairs, indirectly influencing wool development and traits. Studies have shown that the size and number of adipocytes are related to wool diameter [ 95 ], and they also play a non-negligible role in the development and traits of wool. Androgens play an essential regulatory role in the development of sheep hair follicles and have a significant impact on hair growth and development.…”