Summary
Background and Industry Context
LAMBPLAN relies on genetic parameters derived largely from meatsheep breeds. Specific parameters for the Merino will provide more accurate EBVs for carcass and meat quality traits. While there are estimates of heritability for liveweight for the Australian Merino, there are no published estimates to our knowledge of heritabilities and genetic correlations for fat, eye muscle or meat quality traits, nor their correlations with wool traits. Further, to our knowledge, there are no published genetic parameter estimates for pH and colour meat quality traits in sheep.
The Merino contributes at least 50% of the genes for slaughter lamb in Australia. Thus it is important that genetic improvement in meat traits be encouraged within Merino breeding programs. Many Merino breeders are interested in improving the genetic merit of their flocks for meat production and quality, particularly in recent years because of low wool returns. LAMBPLAN is building a client base of Merino breeders who wish to include growth, leanness and muscling as well as meat quality traits in their breeding objectives, along with traditional wool traits. Previous research at Cowra has shown the Merino is leaner and has reasonably comparable eye muscle area to meat breed crosses, when grown under good conditions and compared at the same carcass weights. The results however showed considerable variation between individual Merino sires. The Merino lambs had higher meat pH and poorer acceptability than most other crosses.
Objective
To provide LAMBPLAN with genetic parameters relating to carcass traits in Merinos by June 2001.
Methodology
Data were collected from the QPLU$ Merino selection lines maintained at the Trangie Agricultural Research Centre, which are representative of the three major Merino strains in Australia. Some 1045 19-month old rams from three different strains (fine, medium and broad) born in 1997 and 1998 (progeny of 125 sires and 748 dams) were slaughtered and carcass data collected (carcass weight (HCW), fat depth (FATGR, FATC), eye muscle depth (EMD), width (EMW), meat ultimate pH and colour). A raft of wool and other production records are also collected at Trangie on these animals and their female sibs. The variance components were estimated from an animal model applying a Restricted Maximum Likelihood procedure using ASREML.
Results
The estimates of heritability for carcass traits were 0.33 ± 0.09 for FATGR, 0.20 ± 0.08 for FATC, 0.27 ± 0.08 for EMD and 0.15 ± 0.07 for EMW. Heritability estimates for meat quality traits were moderate for pH (0.27 ± 0.09) and lower for the colour traits (L*, a*, b*). There was some genetic variation for L* colour (h2=0.14 ± 0.07), which measures the relative lightness of the muscle. However there was no genetic variation expressed for the a* and b* colour measurements, that measure relative redness and yellowness respectively.
Multivariate analyses provided estimates of genetic and phenotypic correlations among the carcass and meat quality traits as well as between these traits and wool traits. Subsequent analyses will also provide correlations between reproduction and these carcass and meat quality traits when data becomes available from lifetime lambing records on the female half sibs. The genetic correlations among the carcass and meat quality traits tended to be low to moderate and not significantly different from zero, except for FATC and FATGR
(0.98 ± 0.14) and pH and Colour L* (-0.56 ± 0.23), which were in a favourable direction.
Discussion and Conclusions
The estimates of heritability were generally in the moderate range, with corresponding phenotypic variation, indicating considerable change can be achieved through selection for carcass traits in Merino flocks. The heritability estimates reported here for carcass traits in Merino sheep are within the range of those previously reported for other sheep breeds in Australia and overseas. This would indicate there is need for only minor changes to the parameters currently used by LAMBPLAN for calculating EBVs for meat breeds when Merino data is being processed. Merino breeding programs should put greater emphasis on muscle than fat because the Merino is generally leaner than other meat breeds at the same carcass weight. The lower heritability for FATC than FATGR reflected the importance of ensuring the animals are not too lean at measurement, which affects the accuracy of measurement. The very high genetic correlation between FATC and FATGR (0.98 ± 0.14) emphasises that change through selection in FATC will be closely matched by changes in FATGR.
The study provides the first parameter estimates of meat quality traits in sheep, which indicates there is moderate genetic variation with scope for selection for improvement in meat quality through pH and possibly meat colour. Heritability estimates for meat quality traits were moderate for pH (0.27 ± 0.09) and lower for the colour traits (L*, a*, b*). There was some genetic variation for L* colour (h2=0.14 ± 0.07), which measures the relative lightness of the muscle. However there was no genetic variation expressed for the a* and b* colour measurements, that measure relative redness and yellowness respectively. There was a moderately strong favourable genetic correlation between pH and colour L* (-0.56 ± 0.23).
The heritability estimates for Merino carcass traits are similar to reports for other sheep breeds. It is recommended that these parameters be incorporated into the LAMBPLAN parameter matrix for calculating EBVs for Merino data. The study provides the first parameter estimates for indicators of meat quality traits in sheep, which show there is moderate genetic variation with scope for selection for improvement in meat quality through pH and possibly meat colour.
