Bone-out for MSA Quality Index

Summary

​Meat Standards Australia Australia (MSA) is a cuts based grading system which grades individual cuts in the beef carcass using commercial inputs. By necessity the outputs of MSA are complex but this complexity is warranted in carcasses where muscles differ widely in form and function and hence eating quality. 
There is a need to provide a simple feedback tool by which producers can monitor changes in eating quality of the carcass. Boning groups were set up as a tool to help processors sort carcasses into like groups to facilitate the harvesting of cuts of different eating quality grades.  Initially they were intended to be customised to the type of carcasses processed within each plant.  However as the system evolved boning groups were applied as a national standard across the country on all types of cattle.  As a national system they were inefficient in separating the carcasses into like groups for boning. At the producer level they were difficult to interpret or to use to monitor progress in eating quality.
The concept of a MSA index to describe eating quality of the carcass was proposed as a tool to allow producers to better understand changes in the predicted eating quality of their carcasses.  It was proposed that the MSA Index be calculated as a weighted eating quality score for the whole carcass. This required assumptions as to the cooking procedure used for each cut and a base muscle distribution pattern in the carcass.  A weighted MSA index could be calculated as the sum of the MQ4 for each muscle multiplied by the weight of the muscle as a proportion of total muscle in the carcass. This approach assumed that muscle distribution patterns were relatively constant across the carcass of different breeds, sexes and weight classes of cattle.
There has been considerable research undertaken on factors that influence muscle distribution in beef carcasses.  The conclusion from these studies was that muscle distribution in the carcass was a result of the functional stresses placed on the musculature.  As all cattle undertake similar activities by walking, standing and lying down it was therefore not surprising that between breed differences in muscle distribution were small.
This project examined the distribution of trimmed MSA cuts in the carcasses of steers from three muscling lines. The muscling line were part of a long term project managed by the NSW DPI where replacement animals had been selected for low and high live animal muscling scores. The base cows were from the Hereford breed which were mated to Angus bulls. Inadvertently the mysotatin gene was introduced into the high muscling line in 2005 and this presented an opportunity to create another muscling selection line where the cows had one copy of the myostatin gene.
The range in muscling between these lines was similar if not greater than the between breed difference in muscling that exist in industry.  Carcasses from these lines presented an ideal opportunity to firstly develop a base on which to calculate the MSA Index, but also to investigate the effect of extremes in muscling on muscle distribution.  The inclusion of a line which carried one copy of the myostatin gene provided an extreme in muscling caused by a single gene effect.
The results showed little difference in muscle distribution of trimmed MSA cuts between carcasses from the high and low muscling lines.  The muscle distribution did differ slightly for the myostatin muscling carcasses so they were excluded from the base muscle distribution pattern used to calculate the MSA Index.
A dissection guide was provided to allow the muscle distribution data base to be added to in the future.  This would only occur if producers were concerned that their carcasses differed enough in muscle distribution to warrant a different base distribution pattern to calculate the MSA Index.