Cream from fat on cheap-to-run cows
From the December 2008 edition of Agriculture Today.
I recently read again an article in the CRC’s Science for Quality Beef by my DPI colleague, Peter Parnell, about “cheaper-to-run” cows.
It is a timely topic as we strive for greater production efficiency and adaptability in our variable environment.
Understanding how cows lay down and then utilise muscle tissue and fat is a useful starting point in seeking out cheaper-to-run cows.
It makes a lot of difference whether a cow stores extra weight as muscle tissue or as fat because the tissues have a different concentration of stored energy, and have different maintenance costs.
A kilogram of stored body fat contains about 39 megajoules (Mj) of energy, more than five times that of a kilogram of muscle, which contains about seven megajoules.
A cow can therefore store more energy in the same weight of fat compared to muscle.
Despite this difference, it only takes 25 per cent more energy from feed to store a kilogram of fat compared to a kilogram of muscle.
And once fat is deposited in the body reserves, it takes less than half as much energy to maintain it there compared to the same weight of muscle.
This is because muscle is a much more active tissue than fat and is constantly being turned over.
In a typical cow herd, 70pc of the energy used to maintain cows is used for maintaining muscle tissue, not fat.
So bigger, leaner cows need more energy to maintain themselves and the additional feed required to supply it may be difficult to provide at critical times in the yearly feed supply cycle.
As a consequence production, fertility for example, may suffer.
At any given liveweight, mature cows that tend to store surplus energy as fat tissue should therefore be cheaper to run than those accumulating it as muscle.
Managing the fat score of females at calving is important to maximise herd fertility.
Any change towards leaner cows, whether by selecting for higher carcase yield or improved feed efficiency, or because of poorly designed crossbreeding programs could have serious consequences.
The Beef CRC’s maternal efficiency project will spell out these consequences and present breeders with a balanced story.
The Beef CRC is currently conducting a maternal efficiency research project which will no doubt deliver some interesting outcomes.
