Effects of the Texel muscling quantitative trait locus on carcass traits in crossbred lambs

Abstract

Texel muscling quantitative trait locus (TM-QTL) is a QTL on chromosome 18, originally identified in purebred UK Texel sheep, which was reported to increase ultrasonically measured muscle depth at the third lumbar vertebra by around 4% to 7%. The objective of the present study was to comprehensively evaluate the TM-QTL and to determine whether it could provide benefits to the UK sheep industry through increased carcass meat yield in crossbred slaughter lambs. Effects of this QTL on a range of carcass traits, including those measured in vivo and by dissection, were evaluated in heterozygous carrier and non-carrier lambs produced by crossing heterozygous carrier Texel rams with non-carrier Mule (Bluefaced Leicester 3 Scottish Blackface) ewes from a lowland flock. The TM-QTL was found to increase loin muscling in crossbred lambs at a given live weight or carcass weight, as measured by ultrasound, X-ray computed tomography (CT) and carcass dissection. Depth of M. longissimus lumborum (MLL) was greater in TM-QTL carrier lambs compared to non-carriers as measured by both ultrasound at the third lumbar vertebra (14.5%; P 5 0.033) and CT scanning at the fifth lumbar vertebra (16.7%; P 5 0.004). Width and area of MLL measured using CT were also greater in TM-QTL carrier lambs compared to non-carriers (13.0%; P 5 0.013 and 15.1%; P 5 0.047, respectively). Loin muscle volume measured using CT was greater in TM-QTL carriers than in non-carriers (15.9%; P 5 0.005) and the dissected weight of the MLL was 17.1% greater in TM-QTL carriers compared to non-carriers ( P , 0.001). The proportion of the total carcass lean meat yield (LMY) that was contained within the loin region was slightly higher in TM-QTL carriers than in non-carriers (0.154 v. 0.145; P 5 0.006). However, TM-QTL was found to have no significant effect on the total weight or proportion of LMY or of saleable meat yield in the carcass measured by dissection, or on muscling in the hind leg measured by CT or dissection. This work has verified that the inheritance of TM-QTL is associated with increased loin muscling in crossbred lambs, as has previously been reported for purebred Texel lambs.

Effect and mode of action of the Texel muscling QTL (TM-QTL) on carcass traits in purebred Texel lambs

“…The initial study by Walling et al 2004 showed an effect of +4% to +7% on ultrasound muscle depth, and in a larger population in a follow-on study Matika et al (2011) showed an effect of +8% to +17% in 6 out of 36 Texel families. This effect was confirmed in Texel sired crossbred lambs out of Mule ewes (Macfarlane et al, 2009) and also out of Welsh Mountain ewes (Masri et al, 2011). Macfarlane et al (2009) also noted that loin muscle (M. longissimus lumborum) width, area, volume and weight were also higher in lambs inheriting TM-QTL from their sire.…”

“…This effect was confirmed in Texel sired crossbred lambs out of Mule ewes (Macfarlane et al, 2009) and also out of Welsh Mountain ewes (Masri et al, 2011). Macfarlane et al (2009) also noted that loin muscle (M. longissimus lumborum) width, area, volume and weight were also higher in lambs inheriting TM-QTL from their sire.…”

“…Of further interest was the effect TM-QTL had on carcass and joint composition. In previous work looking at the effect of a single copy of TM-QTL in crossbred Texel-sired lambs, there did not appear be an effect on other carcass traits (out of Mule ewes, Macfarlane et al, 2009;out of Welsh Mountain ewes, Masri et al, 2011). In the present study, lambs inheriting TM-QTL from their sire (either homozygote or heterozygote carriers), tended to be less fat than wild-type homozygotes and this translated to a commercially relevant significant difference in weight of fat trimmed from the carcass during butchery (−11%) between homozygote wild-types and heterozygotes inheriting TM-QTL from the sire.…”

“…Blood samples were genotyped for five microsatellite markers on OAR18 (MCMA26, CSSM18, OY5, OY3 and OARTMR1) at the Animal Genomics Group, AgResearch Invermay, New Zealand. Marker data collected each year were used along with previously collected data to classify all animals for genotype status for TM-QTL, as described by Macfarlane et al (2009 and2010). The information produced was used each year to plan matings within the flocks, in order to increase the frequency of TM-QTL whilst limiting inbreeding.…”

“…In this original study, the effect of carrying a single copy of TM-QTL inherited from the sire was a 1 to 2 mm increase in ultrasound muscle depth (+4% to + 11%). In a further study using crossbred lambs sired by Texel rams heterozygous for TM-QTL, with Mules or Welsh Mountain ewes as their dams (Macfarlane et al, 2009;Masri et al, 2011) reported a 4% to 11% effect on muscling, specific to the loin region, of carrying a single copy of the QTL. No effect was observed on other carcass traits.…”