Stock Weighing Protocols
To establish - average weight of the mob
- the range of weights in the mob
- use to monitor weight changes and growth rates
1. Weigh at the same “time off feed” each time you weigh (lambs may contain 5kg gutfill, so weighing them empty the first time and full the second time can give impressive, but false, growth rates).
- It is often easiest to weigh straight off the paddock but consistency is the important thing.
Whenever you weigh, do it the same each time.
2. Use a check weight to check your scales and adjust if necessary. (eg, 25 kg bag of Zinc Sulphate, or, a drench container filled with sand and weighed at your stock firm or wool brokers - write the weight on the container).
3. Use the liveweight recording sheets supplied for at least two of the weighings for each stock class. This will give you a much better picture of the range, size of the bottom end, etc, than you will get by just calculating the average.
4. Transfer the weighing results to the reporting form for the appropriate period (eg May - August).
5. How many should you weigh?
(A) For mobs of even weight and size - minimum of 30, preferably 50
(B) Mobs of uneven weight and size - minimum of 80 preferably 100 (if a significant
number of animals are more than 5kg over or under the average).
6. The stock chosen should be a random selection representing the whole mob. If a large mob is
coming through the yards, take an equal sample from the front, middle, and back of the mob.
7. 95% range of weight. This is the difference in kg between the heaviest and the lightest animal
after you have excluded the top and bottom 3 weights. (This gives a better feel for the real range
by excluding the “freaks” at either end).
Note: Additional weighings may assist your management and we encourage you to do so.
Chart KS 2 (LAMB GROWTH CALCULATION)
Days From Weaning
Total lamb days ( B )
= ………………….. ( C ) Average Days (weaning to slaughter)
Number killed ( A )
To calculate average growth rate (grams per day)
Average liveweight at slaughter
ðTotal kg lamb c.w……………..
(From killing sheets)
Average weaning weight
÷ Total number of lambs…………
Divide by figure ( C )
= Average carcass wgt……………
40% yield ÷ 0.4
Average growth rate
= Avg liveweight at slaughter…………….
AVERAGE LAMB GROWTH
On sheep farms lamb growth is one of the most important factors affecting profitability.
Fast growth allows slaughter weights to be reached faster. While lambs may be eating more per day when they are growing quickly, the total feed required is substantially less than an animal growing slower to reach the same weight.
When lambs grow faster, it enables numbers to be reduced earlier. This frees up feed for ewes or other stock and may be used to increase pasture cover going into the winter, reducing supplementary feed requirements and cost.
Better fed ewes will tend to have more lambs, milk better, and wean better lambs giving you a head start into the next lamb growing season. improved autumn and winter feeding of ewes is a key part of achieving this.
How to calculate your average lamb growth:
To fill in the chart over the page (KS 2) you put in the slaughter date, days from weaning and number killed for each of your drafts. You then follow the instructions for the calculations.
You will also need to calculate your average lamb liveweight at slaughter for the season (divide average carcass weight by 0.40), and the actual average weaning weight or your best estimate of it. (In South Otago weaning weight typically ranges from 20-27kg - remember this is the average of all your lambs, not just the best mobs!).
How does your lamb growth measure up:
1. Below 100 g/day - poor growth, considerable improvement possible.
2. 100 - 150 g/day - average, plenty of improvements possible.
3. 150 - 200 g/day - above average, still room for improvement.
4. 200 - 250 g/day - very good.
5. Above 250 g/day - exceptional.
If your lamb growth falls into group 1 and 2, there are many ways to improving it. It doesn’t have to cost a lot either. Some improvements may require investment in new pastures, etc, which will provide a good return for your investment.
Above all, invest in some advice to help make the best decision.
Information and charts supplied by Agriculture New Zealand, Balclutha.
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