The effects of divergent selection for reproduction and sex on quantitative and qualitative slaughter traits in Merinos

The impact of selection of sheep for reproduction on meat traits are not evident, while genetic parameters for meat traits is absent for South African pure breeds. Quantitative and qualitative meat traits were therefore studied in progeny of two Merino selection lines that were divergently selected for number of lambs weaned per ewe joined (NLW) since 1986. The historic divergent selection resulted in two lines (High (H) and Low (L)) differing widely for NLW. Slaughter data were recorded during the routine slaughter of surplus 14-month-old ram and ewe hoggets from these lines and assessed for selection line and sex. Single-trait heritability estimates were derived for meat traits by average information restricted maximum likelihood methods. Depending on the trait, data were available for between 340 and 576 animals that were recorded between 2015 and 2018. Hoggets from the H line were heavier than their L line contemporaries, with a slightly lower ultimate pH after 48 h in the cooler and slightly darker meat. H line ewes had, on average, redder meat than the other selection line x sex groups. Single-trait heritability estimates amounted to 0.44 ± 0.16 for slaughter weight, 0.63 ± 0.15 for carcass weight, 0.34 ± 0.15 for dressing percentage, 0.25 ± 0.11 for fat depth at the 13th rib, 0.29 ± 0.11 for fat depth at the rump, 0.12 ± 0.11 for ultimate pH, 0.32 ± 0.12 for lightness, 0.11 ± 0.09 for redness, 0.04 ± 0.06 for yellowness, 0.05 ± 0.08 for cooking loss and 0.06 ± 0.07 for drip loss. Parameter estimates for initial pH and shear force of the meat went to the boundary of parameter space and were not estimable. It was concluded that selection for NLW did not compromise any of the meat traits and that most quantitative meat traits were heritable and variable, making selection for improvement of these traits feasible. Additional research is indicated on the qualitative meat traits studied.