Effects of a quantitative trait locus for increased muscularity on carcass traits measured by subjective conformation and fat class scores and video image analysis in crossbred lambs

Abstract

A quantitative trait locus (QTL) for increased loin muscularity (TM-QTL) has previously been identified in purebred Texel sheep. Crossbred lambs born out of Mule ewes mated to heterozygous Texel sires for the TM-QTL were evaluated for a range of carcass traits. Lambs were genotyped and classified as carriers (n 5 62) of a single copy of the TM-QTL and non-carriers (n 5 49). In this study, the effects of the TM-QTL on carcass attributes were investigated using subjective classification scores for conformation and fatness, and measurements from a video image analysis (VIA) system. In addition, refined prediction equations to estimate weights of primal joints (leg, chump, loin, breast and shoulder) were obtained by calibrating the VIA system against computer tomography (CT) measurements in the loin region. The new refined prediction models increased the accuracy of prediction of all primal cuts on an average of 16% compared to previously derived standard VIA prediction equations. The coefficient of determination (R 2 ) of the VIA system to predict in vivo CT measurements ranged from 0.39 to 0.72 for measurements of Musculus longissimus lumborum (MLL) area, width and depth, lumbar spine length, loin muscle volume and loin muscularity index. Using VIA estimates of CT-measured loin muscle traits, a significant increase in depth (12.7%) of the MLL was found to be associated with the TM-QTL. Conformation and fatness scores and the shape of the carcass measured as individual lengths, widths and areas by VIA were not significantly influenced by the TM-QTL. Primal meat yields estimated using both standard and refined VIA prediction equations were not significantly affected by the TM-QTL. However, carcass 'compactness' was found to have significantly increased in carrier lambs. The weight of the dissected MLL estimated using VIA information was greater (12.6%) for carriers compared to non-carriers. To conclude, neither the current industry carcass evaluation system for conformation and fatness nor the standard VIA system is able to identify the effect of the TM-QTL in the loin region in the moment. However, the calibration of the VIA system against CT measurements resulted in improved VIA prediction equations for primal meat yields and also showed moderate potential to estimate loin muscle traits measured by CT and to detect, partially, the effect of the TM-QTL on these traits. Keywords: lamb, carcass quality, conformation, video image analysis, QTL ImplicationsThis work is the first evaluation of the effects of a quantitative trait locus (QTL) for increased muscularity on a wide range of carcass traits measured by subjective conformation and fat class scores and video image analysis (VIA) in crossbred lambs. The work is important in providing information on the potential of the subjective conformation and fat class scores and automatic VIA to estimate the QTL effect on carcass composition and to help provide the basis for the development of a value-based marketing system. The present work together with other ongoing work o...

The effects of a loin muscling quantitative trait locus (LoinMAX™) on carcass and VIA-based traits in crossbred lambs

“…This result is similar to that reported for TM-QTL by Rius-Vilarrasa et al (2009b), who found that crossbred lambs from a similar genetic background to those in our study carrying one copy of TM-QTL showed no significant difference in conformation and fat class scores compared with non-carriers. The results of this study indicate that the current industry carcass evaluation system would not be able to detect the improvement in loin muscle characteristics offered by LM-QTL.…”

“…Rius Vilarrasa et al (2009a) reported that VIA achieved consistently higher accuracy and precision in predicting the carcass primal cut weights and SMY compared with the MLC classification grading for carcass conformation and fat class, which is in use in UK abattoirs. Rius-Vilarrasa et al (2009b) didnot detect significant difference in VIA-predicted loin dimensions and primal cut weights between TM-QTL carrier and non-carrier lambs using the standard prediction equation produced by E 1 V Technology, Germany. By contrast, deriving refined prediction equations by calibration against CT measurements it was possible in this previous experiment to detect a significant increase in MLL depth in TM-QTL carrier lambs.…”

“…Calibration and validation under British abattoir conditions were previously undertaken by Rius-Vilarrasa et al (2009a). Two different prediction equations were used to estimate carcass cuts the 'standard' equations derived by E 1 V Technology, Germany, and the 'refined' equations later developed by E 1 V Technology, Germany, which were derived using calibration of the VIA system against CT measurements in the loin region (Rius-Vilarrasa et al, 2009b). Higher accuracy and precision of prediction of carcass primal and trimmed primal cuts achieved with these refined prediction equations, compared to the 'standard' VIA prediction equations, were reported by Rius-Vilarrasa et al (2009b).…”

“…Two different prediction equations were used to estimate carcass cuts the 'standard' equations derived by E 1 V Technology, Germany, and the 'refined' equations later developed by E 1 V Technology, Germany, which were derived using calibration of the VIA system against CT measurements in the loin region (Rius-Vilarrasa et al, 2009b). Higher accuracy and precision of prediction of carcass primal and trimmed primal cuts achieved with these refined prediction equations, compared to the 'standard' VIA prediction equations, were reported by Rius-Vilarrasa et al (2009b). The correlation between muscle weight derived by CT scanning and the sum of trimmed primal weights predicted using refined VIA prediction equations was higher in this study (r 5 0.87) than the corresponding correlation based on the standard prediction equations (r 5 0.85).…”

Genes Contributing to Genetic Variation of Muscling in Sheep

“…In Texel and Texel–Suffolk families another confirmed muscling QTL (TM-QTL) was localized to 2 cM telomeric of the same marker (CSSM18) on OAR18 (Walling et al, 2004; Macfarlane et al, 2009, 2012; Rius-Vilarrasa et al, 2009; Matika et al, 2010). The muscling phenotype in these animals was similar to that in the Poll Dorset sheep and associated with altered muscle shape–the carcass was described as more “compact.” It was recently concluded there is evidence for imprinting of this QTL.…”