2014-02-26   facebooktwitterrss
Lamb – The Inefficiency of Too Much Fat

Fat is a late-maturing tissue, with most of its development happening after bone and muscle, and the proportion of fat in the body increases as the animal matures.

Excess fat has to be trimmed in the abattoir, so the saleable meat yield can be proportionally lower for out-of-spec carcases as weight increases.


© Jennifer Mackenzie

An EBLEX-commissioned review on the inefficiencies of too much fat in sheep identified factors affecting the level of fat. This should help relate the cost of carcase gain to the value of gain, for optimum sale weight and profitability.

Breed has an impact on fat deposition. For example, CT scanning has shown carcase fat weight increased more quickly with growth in Scottish Blackface lambs compared with Texel lambs, which resulted in an increased fat proportion within the carcase.

There is also a difference between sexes, with female lambs having about 2% more fat within their carcases.

Change in the ratio of fat trim to saleable meat yield in relation to the age of female lambs

Change in the ratio of fat trim to saleable meat yield in relation to the age of female lambs

Fat tissue will normally be about 30% of the carcase weight, but the proportion does increase as the animal matures. The work by Scotland’s Rural College suggests that as the animal ages there is a greater increase in fat trim compared with saleable meat. It can be seen in the example below that at 100 days the fat trim was 50g for each 1kg increase in saleable meat yield, while at 200 days the fat trim equates to 75g/kg.

Lean tissue is comprised of 74% water, 20% protein and 5% lipid, whereas fat tissue is 24% water, 9% protein and 67% fat. This helps explain why the energy needed for liveweight gain increases as the animal ages and fat deposition increases, with fat deposition requiring four times more energy than is needed for lean tissue.

Fat trim was found to increase from 3.5 to 5% when an animal moves from a 2 to a 3H grade, which is predicted to take an average of 90 days for castrated lambs or 47 days for female lambs.

It is important to remember that extra carcase weight does not mean a similar increase in saleable meat yield, as fat trim increases as the animal ages and increases in weight.


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