Item 1, Topic 1
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7.2.1 Within breed variation

The impact of processing factors on estimates of genetic variance will depend upon whether they have an environmental or genetic component. If cold shortening occurred because the carcasses were in a section of the chiller that received a much greater chilling effect, estimates of genetic variance would be biased down. However if the cold shortening effect was because the carcasses were leaner and chilled faster, and leanness as a trait has a strong genetic component, then the estimates of genetic variance would be biased upwards. The latter scenario is one that has often occurred in many genetic studies where there has been little control over post-slaughter conditions.


Results from the CRC’s core program suggest that if cattle are handled well prior to slaughter, and there is minimal variation in factors such as pH fall and carcase chilling temperature, then there is little progress to be made from within breed selection for tenderness in Bos taurus cattle, although this does not appear to be the case for Bos indicus cattle.


Genetic correlations between the same objective trait between the M. longissimus dorsi and M. semitendinosus muscles were generally low and variable (D. Robinson pers. com.).  This is perhaps not surprising as the M. longissimus dorsi has a low connective content and is susceptible to shortening during the onset of rigor, whilst the M. semitendinosus muscle has a high connective tissue content and in the normally hung carcass has sufficient tension applied during rigor to minimise any impact of shortening.  Other studies have also commented on the generally poor relationship between tenderness in muscles within a carcass and the difficulties in using the M. longissimus dorsi as an indicator of carcass quality (Matthews et al. 1998).


The MSA grading scheme has focused on consumer sensory scores as the means of describing beef palatability.  The CRC core breeding program provides an opportunity to obtain sensory measurements processing samples through the MSA consumer panels.  By the end of the program this will comprise a total of just under 5,000 animals from pedigreed herds on which sensory data is available, which will allow estimates of genetic parameters of beef palatability to be estimated for Australian populations.