Relationship of ewe reproduction with subjectively assessed wool and conformation traits in the Elsenburg Merino flock

Abstract

Subjectively assessed wool and conformation traits are widely used to select breeding ewes and rams in the sheep industry. Data from a Merino flock that is maintained at Elsenburg Research Farm were used to investigate animal model (co)variance components for ewe reproduction traits with subjectively assessed wool and conformation traits. Ewe reproduction traits were assessed at their first lambing opportunity at two years, or over a three-year period from their lambing opportunities at two to four years old. Relationships of ewe reproduction traits with subjectively measured wool and conformation traits were also investigated. All these traits were heritable, with a range from 0.16 ± 0.03 for topline (TOPL) to 0.64 ± 0.04 for woolly face score (WFS). Genetic correlations of number of lambs born (NLB1) with colour (COL), number of lambs weaned (NLW1) with COL and belly and points (BANDP) and total weight of lamb weaned (TWW1) with COL were negative and significant. Significant genetic correlations of ewe reproduction traits over three lambing opportunities were found between number of lambs born (NLB3) and WFS (0.23 ± 0.11) and between total weight weaned (TWW3) and face cover score (FCS) (-0.33 ± 0.16). Among these traits, the noteworthy favourable genetic correlation between total fold score (TOT) and NLB1 suggested that plainer ewes were more reproductive. This is important for the South African Merino industry as plainer sheep are more desirable because of their faster growth and higher lambing percentages and reduced chances of fly strike. Selection for improved ewe reproduction in Merino sheep thus would not result in marked unfavourable correlated responses in most of these subjective wool and conformation traits.

Substantial genetic gains in reducing breech flystrike and in improving productivity traits are achievable in Merino sheep by using index selection

“…The predicted increases in genetic gains for reproductive rate of 10-30% when using a FP+FS index is an added potential benefit for fine-wool breeders aiming to reduce FS and is consistent with research findings that plainer-bodied sheep are genetically likely to wean more lambs (Dun 1964;Dun and Hamilton 1965;Turner and Young 1969;Greeff et al 2012;Matebesi-Ranthimo et al 2018). However, strong selection emphasis on reducing FS (economic values in excess of -$60 to -$80/strike.sheep per year) when using a MP+FS and especially a DP+FS index may noticeably reduce genetic gains for NLW and would require careful evaluation before use in breeding programs.…”

The Effect of Integrating Genomic Information into Genetic Evaluations of Chinese Merino Sheep

“…Furthermore, the standard error of heritability for SC was lower in the present study. The present heritability estimates for CRIM and OIL were lower than those reported by Matebesiet al [44][45][46]. Nevertheless, the heritability estimates for CRIM and OIL based on pedigree or genomic information were lower, indicating that subjectively-assessed wool traits are greatly influenced by environmental factors.…”