Making More from Sheep Australian Wool Innovation Limited Meat & Livestock Australia
MODULE 9: Gain from Genetics
Tool 9.9
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This tool demonstrates a simple method of calculating the value of improved growth rate. Use post weaning weight ASBVs to estimate the value that genetic improvement in growth rate can bring when choosing between two rams. Remember - the predicted progeny difference is half the difference between the ASBVs. Follow the steps to calculate the value to your flock.

  Post weaning weight ASBV
Ram A 11
Ram B 7
ASBV difference (11 – 7) 4 kg
Predicted progeny difference (4 / 2) 2 kg



The predicted weight difference between progeny of these rams at 7.5 months of age is 2 kg (half the difference between PWT ASBVs because lambs get half their genes from the sire).

Predicted progeny live weight difference 2 kg


Predicted difference in carcase weight (CWt) assuming 46% dressing

Predicted progeny CWt difference (2 x 0.46) 0.92 kg


Assume your rams are joined at 2% for 4 years producing 100% lambing.

50 ewes joined per year x 100% lambing x 4 joinings

50 x 1 (100%) x 4 = 200 lambs


Now multiply the number of lambs produced by the predicted difference in CWt (200 lambs x 0.92 kg CWt)

Total predicted gain in carcase weight (CWt)  =184 kg
Average price received (¢/kg CWt)  = 400¢/kg 


Finally, multiply the average price received by the total predicted gain in CWt (3.00 x 184) to give the:

Value of total predicted gain in carcase weight  = $736

Ram A will provide an additional 184 kg carcase weight if joined to 50 ewes with a conception rate of 100% for 4 years. Assuming an average price of $3.00/kg, Ram A will deliver an additional $565 in value compared to Ram B.