Grading ‘raw’ products
When first harvested, wool and meat are known as ‘raw’ products.
Carcasses and wool are put into grades or classes based on their specific characteristics (a result of genetic differences between the animals and the way they have been farmed). This allows processors to select the exact product they want, and farmers to be paid according to the quality and type of wool or meat.
Most carcass characteristics are related to the amount of saleable meat. Generally, as carcass weight increases, saleable meat yield (SMY) increases, because the percentage of bone decreases. However, as carcasses become more fatty, SMY declines because more fat has to be trimmed off to meet market requirements. Carcasses which are thicker and more rounded have a slightly higher SMY, due to a higher lean-meat-to-bone ratio.
The New Zealand Meat Classification Authority system classifies beef carcasses into four types – steer, heifer, cow and bull – according to the sex and maturity of the animal. These are classified further depending on their fat content and muscling. Lamb carcasses destined for export are classified using a similar system.
A typical classification of a beef carcass would be 270 P2 Steer, which is:
- a steer (a male cattle beast castrated when young)
- a 270-kilogram carcass
- P fatness – a light to medium fat cover, 3–10 millimetres deep
- muscling class 2 – good muscle development.
Measuring muscle and fat
Historically, carcass weight has been measured using scales, while fatness and muscling were visually assessed by a grader. Since the late 1980s, graders of lamb carcasses have also used a metal probe to determine the fatness grade. In the early 2000s, computer digital image analysis was being used to assess the SMY and value of lamb carcasses.