7.2.2 Between breed variation
Of all the MSA criteria, specification of content is obviously the most contentious. A number of researchers (both overseas and Australian) have reported that as percentage increases, tenderness or palatability of the meat decreases. The magnitude of the breed effect tends to vary considerably between studies and as suggested by Hearnshaw . (1998) may interact with processing conditions.
22.214.171.124 The interaction of breed effects with processing conditions
A number of studies (both Australian and US) have shown that the effect of content may interact with processing conditions. In a recent experiment conducted by Hearnshaw . (1998) this interaction was particularly evident with a large breed effect being evident in non-stimulated carcases, which contrasted the stimulated carcases where the breed effect was not evident. It is interesting that this effect cannot be reliably repeated in other experiments (e.g. the BICE experiment in Figure 7.1). One possible mechanism by which the interaction is occurring is that the Brahman carcases are less fat and therefore without stimulation tend to whilst shortening does not occur in the fatter carcases.
However from a commercial perspective, content was generally confounded with harsher environments, poorer nutrition, less handling and greater transportation distances to slaughter and the results from the MSA database are perhaps more relevant to the importance of the content as a grading criteria. The MSA database shows that for cattle that are being processed under commercial conditions content has a large effect on palatability of the striploin (Table 7.4). Certainly for the carcase pathways scheme where non-negotiable hurdles were used as thresholds to the grades, the early results showed that Bos indicus content had a large effect on palatability. Based on striploin palatability data from the database, those carcases that were classed as having greater than 75% content (based on phenotype) had a palatability failure rate (i.e. a CMQ4 score of < 48) of 63%. For low content carcases the palatability failure rate was reduced to 11%. Based on this information the pathways carcase system initially had a threshold of 25% on content, although this was later raised if the carcases were tenderstretched. Therefore under present processing conditions breed is an important component of the MSA criteria. However given the interaction with processing conditions, the importance of breed needs to be continually reassessed as new or modified processing conditions are introduced.
126.96.36.199 The interaction of breed effects with cuts
188.8.131.52 Possible mechanisms for the breed effects
Mechanisms, which contribute to the effect on palatability, have been investigated in several studies. Johnson . (1990) reported breed differences in the proteolytic , with the high content animals having higher levels of calpastatin (an inhibitor of the ageing enzymes). Shackelford . (1992) estimated that the of post-rigor activity to be of the order of 0.70. Gursansky, (pers com) reported differences in values, which would implicate the heat stability of the connective tissue matrix. More recent studies by the CRC (Ferguson pers com) suggest that there are breed differences in the composition of the phospholipid component of the cell membranes, which give rise to differences in calcium permeability and consequently impact on muscle shortening. This is consistent with the interaction between effect and processing, whereby stimulation can sometimes minimise breed effects in palatability (Hearnshaw . 1998). In addition, the recent MSA results indicate that the breed effects on palatability are not constant across all cuts. It is likely therefore that a number of mechanisms may contribute to the effect, rather than one simple mechanism.