Intramuscular fat levels in sheep muscle during growth

Abstract

A 5 × 4 factorial experiment was designed in which lambs representing five genotypes were slaughtered at four ages (110, 236, 412 and 662 days of age). The genotypes represented were Poll Dorsetgrowth × Border Leicester Merino, Poll Dorsetgrowth × Merino, Poll Dorsetmuscling × Merino, Merino × Merino and Border Leicester × Merino. Both sexes (ewes and wethers) were represented for each genotype and slaughter age combination. In total, 595 animals were slaughtered and the carcass composition and intramuscular fat were measured. Carcass composition [fat, ash and protein (lean)] was determined by dual energy X-ray absorptiometry, with the intramuscular fat percentage determined using near-infrared spectroscopy following removal and weighing of the entire longissimus thoracis et lumborum (LL) muscle. Analysis revealed that the proportion of intramusular fat in the loin relative to total carcass fat decreases as animals mature, thus indicating that intramusular fat deposition occurs early in the maturation of sheep. Furthermore, as animals became heavier and older the accretion rate of intramuscular fat in the LL muscle slowed down. Both genotype (P < 0.05) and sex (P < 0.001) were found to impact on this pattern, with Border Leicester × Merino animals exhibiting the largest increase in intramuscular fat proportion in the LL muscle (4.92 and 5.50% at 22 months of age for ewes and wethers, respectively). The Poll Dorsetgrowth × Border Leicester Merino animals were found to have the greatest absolute levels of intramuscular fat in the whole LL muscle (80.95 and 97.60 g at maturity for ewes and wethers, respectively). The amount of intramuscular fat significantly increased as the sheep became older and fatter; however, these differences were quantitatively small. As such, finishing prime lambs to high levels of total carcass fatness would have little effect on any eating quality benefits associated with increased intramuscular fat proportion.

Intramuscular fat in lamb muscle and the impact of selection for improved carcass lean meat yield

“…When CT lean% was included in the ASBV model, the impact of the breeding values on IMF% was reduced, however, still significant, which indicates that CT lean% does not account for all the variation in IMF%. As with previous studies, increasing HCWT was associated with an increase in IMF% of the M. longissimus lumborum (McPhee et al, 2008;Pannier et al, 2014a); however, the variation in the association across muscles has not been previously reported in Australian sheep. In particular, the large increase in IMF% in the M. supraspinatus of the Merino sired lambs is a unique finding, the reason for which is not currently known.…”

“…The average age in days of these kill groups was 167, 238, 280 and 355, therefore the linear increase in IMF% with age aligns well with the impact of maturity on adiposity as has previously been observed in the M. longissimus lumborum (McPhee et al, 2008;Pannier et al, 2014a). Nonetheless, other factors that may also have impacted, such as changing nutrition/pasture quality across this period cannot be completely discounted.…”

“…These results are in contrast to those of Pannier et al (2014a) who found no differences in IMF% between sire types in the M. longissimus lumborum, although when compared at the same HCWT, the Merinos had the highest IMF%. The Border Leicester-Merino dams produced lambs with more IMF% in four muscles, although the effect was not as large as had been previously reported in the M. longissimus lumborum McPhee et al, 2008;Pannier et al, 2014a). This affect is likely to align with greater whole body adiposity in the Border Leicester-Merino dams, an assertion supported by the inclusion of CT lean%, which accounted for the difference between dam breeds.…”

“…Given that the loin musculature contains the most valuable cuts in the carcass, previous research has focused on the eating quality and IMF% of this muscle (McPhee et al, 2008;Pannier et al, 2014a and2014c). The IMF% of muscles other than the M. longissimus lumborum has not been well described in lamb.…”

Spirulina Supplementation, Sire Breed, Sex and Basal Diet Effects on Lamb Intramuscular Fat Percentage and Fat Melting Points

“…Meats rich in unsaturated fatty acids and low fat melting point (FMP) have been associated with increased palatability and consumer health benefits from reduced risks of cardiovascular disease (Woods & Fearon, 2009). However, unbridled focus on lean meat production may have a negative impact on intramuscular fat percentage (IMF) which is closely aligned with the fundamental meat eating qualities of tenderness and juiciness (Hopkins et al, 2007, McPhee et al, 2008. Fortunately, FMP and IMF can both be manipulated by strategically managing the basal diet and supplementary feed intake of lambs.…”