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Published 02/02/2010 | 05:00
Putting excess fat on carcasses is waste-ful and expensive. It reduces feed efficiency and increases the cost of gain. There is no place in beef production for animals that are kept to fat class 4=,4+ and 5. The target should be to market cattle at fat classes 3 and 4-.
There will be times, when market prices are increasing, that it will pay to let stock into the 4= fat class. At the other end of the scale, it is often difficult to get up to fat class 3 with animals that have a capacity for high muscle growth (lean meat), even at high carcass weights. These are typically bulls of the continental breeds, especially Belgian Blue, Blonde d'Aquitaine, Charolais, but also steers of these breeds.
As cattle get heavier, the proportion of fat in the carcass increases. The rate at which this happens and the final proportion of fat depends on the breed and sex, and can be modified by feed type.
As indicated, the larger continental breeds can go to the high slaughter weight (730kg live, 400kg carcass) while still remaining on the desirable fat classes of 3 and 4-. The traditional breeds need to be slaughtered at weights of around 550kg, (290kg carcass), and crosses between the traditional and continental breeds should be slaughtered at appropriate intermediate weighs. Heifers reach suitable fat cover lighter than steers, which in turn have more fat cover than bulls at specific weights.
Feed efficiency falls with increasing fatness. It takes at least 2.25 times as much energy to produce a kilogramme of fat on a carcass as one of muscle (lean meat). At fairly constant and limited energy intake -- limited by energy concentration and intake capacity -- the rate of carcass gain will fall as the animal increases its fat deposition coming close to finishing weight. For example, if we take a steer on a high energy diet costing €2.20/day, gaining at 1.5kg/day (1kg carcass) early in the finishing period, the cost/kg gain comes to €2.20. Towards the end of the period the gain will fall to about 1.20kg/day (0.84kg carcass) and the cost/kg of gain rises to €2.62. The animal is consuming the same amount of feed but the return is less.
As fat score moves into 4+ and 5 range, the cost of feed is higher than the value of daily carcass gain, and money is lost unless there is a continuous price rise. This is even before any penalties for over-fat carcasses. The most recent adjustments to the payment grid, where the 4= fat grade remains in place and the penalties on the 4+ fat grade are reduced, will help get even more well-finished cattle (heifers) through without deductions.
For all that, the number of over-fat carcasses has been a diminishing problem over the past decade. The table (above) shows the trend in fat stores for steers from 2000 to last year.