"The country just isn't holding up like it used to." This was a comment I heard recently from a family that used to run 2000 head no worries, but the country just isn't looking as healthy now. So what has changed? Soil health, die back, pasture run down, drought? These could have an impact, however in this case (and many others our team sees) it was a result of not understanding animal unit ratings and the impact of increasing mature cow/ewe size.
RCS uses DSE (dry sheep equivalent) and LSU (large stock units) as the two main units, developed in the 1990s. You might also use AE (adult equivalents).
These ratings account for three primary factors that determine the feed intake of animals:
- The average weight;
- The average daily weight gain in growing animals; or
- The breeding status of breeders (dry, pregnant or lactating).
For sheep, we also look at Merino vs crossbred and the number of twins vs singles.
Genetic selection has resulted in mature cow/ewe size increasing substantially over the past few decades. Bigger weight means that the animal eats more! So while this family were still running 2000 head, the increase in mature weight meant that their stocking rate (the amount of feed their animals were eating) had increased without them realising.
They had increased their mature cow weight from 475kg to 525kg over 15 years. The 475kg cows used to average 1.66 LSU for the year (a total of 3320 LSU) whereas the 525kg cows now average 1.76 LSU (a total of 3520 LSU). These LSU ratings are an average rating over 12 months, presuming she is lactating for seven (the animal rating more than doubles when lactating compared to a dry animal).
The 50kg increase resulted in a 6 per cent increase in the number of units they are running. This is the same as running an extra 120 cows. I asked the family if 15 years ago they could have handled an extra 120 cows. They quickly said "No, that would be too many for this block."
We are seeing the same thing in sheep as the mature ewe size is growing quickly along with the twinning rates. These two combined are dramatically increasing the stocking rate for the same number of ewes.
What has changed in your herd/flock? For free access the full LSU and DSE tables, go to aucalc.rcsaustralia.com.au.
Combine this increase in LSU and DSE with the declining rainfall in many areas and you'll be sure to notice an impact on land health.
- David is chairman of agricultural consulting and education company, RCS Australia. www.rcsaustralia.com.au 1800 356 004