Sunday, April 21, 2024

The fat dilemma

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The conflict between what the meat processor wants and what the cow herd owner wants looks set to continue after recently completed Australian research shows the importance of carcase fat in breeding cows. The Beef CRC research (partly funded by Beef + Lamb NZ) highlighted that while the genetic progress made in all other carcase traits will satisfy processors, fat remains an important carcase component in a beef-breeding cow herd. The degree of fatness required depends upon herd management.
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If few or no supplements are fed, particularly in the winter, a female which has the ability to lay down fat during the spring flush, then mobilise it when times are tough, is more productive than one which can’t.

While this process is biologically inefficient (40% of the energy is lost during the process), the low cost of feed during the spring flush and the relatively high cost of it during the winter more than compensates for this.

If supplements are used to maintain cow condition, leaner females can be as efficient.

The issue then becomes one of profitability which depends heavily on the cost of supplementation.

The heifer story is a bit more complicated than that of the mature cows. Heifers were mated at about 400 days-of-age and 360kg bodyweight. While the fatter ones (20% more body fat) had a significantly higher pregnancy rate than the leaner ones, bodyweight also had a major influence. This was particularly so if the mating period was confined to six weeks. The rebreeding rate of lactating, first-calving heifers favoured the fatter heifers, but the expected crash in the pregnancy rate for the leaner heifers on low levels of nutrition did not occur.

Take home messages:

  • Selection to improve carcase traits does not appear to be affecting herd profitability
  • The degree of importance of rump fat in breeding females depends upon the harshness of the environment
  • Fat cows had a 12% higher pregnancy rate after a six-week mating period than lean cows, but this difference was less if the mating period was for nine weeks
  • The difference in efficiency between fat and lean cows is relatively small, but lean cows do need more supplements
  • The difference in profitability depends on the cost of these supplements
  • Females that get in calf late tend to remain late for the rest of their productive lives
  • Mating weight and fatness are both important in achieving high pregnancy rates in heifers, particularly if there is a short mating period.
  • Heifers should be 65% of their mature weight when joined
  • Heifers not in calf after six weeks should be culled
  • The days-to-calving EBV is the best available predictor of pregnancy rate
  • Muscle has a positive effect on cow performance.
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