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Genetic Indexes Explained

Measuring Genetic Merit

Measuring and monitoring are key to our goal of constantly improving our sheep genetics. All stud animals are evaluated for genetic merit through nProve – Sheep Improvement Ltd (SIL). nProve – SIL is New Zealand’s genetic engine provided by Beef + Lamb New Zealand Genetics. It generates the estimated breeding values for different traits and the economic indexes.

NZ Maternal Worth (NZMW) – Dual Purpose Production Index (DPP)

The NZMW – Dual Purpose Production Index (DPP) is the sum of all the trait indexes added together. Below is a simple explanation of how the NZMW- DPP index helps sheep breeders select the animals that will provide the greatest economic benefit to their flock.

Indexes below are expressed in cents of value above an average stud sheep in 1995.

Purchasing a ram with a DPP of 2000 means a sheep breeder has purchased a ram with genetics of $20 greater value than a ram with a DPP of 0. For example, if the genetic merit of a commercial sheep flock is on average DPP 500 (i.e. $5.00 greater than stud sheep in 1995) and the farmer buys a ram with a DPP of 2000: this ram will pass on half of his genetics to his progeny ($10.00). The other half of his progeny’s genetics will come from the dam ($5.00). Consequently the progeny will be have a DPP of 1250 or $12.50.

Assuming both rams are of equal health, eczma tolerance and soundness. A ram buyer can quickly assess the cost benefit of two different rams by looking at their DPP index.

An Example of Comparing Rams using the DPP Index

A ram with a DPP of 2500 compared with another ram with a DPP of 1500 has $10.00 greater value. While this doesn’t seem a lot, when that ram goes across 100 ewes lambing at 140% each year for 3 years minimum, then he sires 420 progeny.  Because each of his progeny gain half of their sire’s genetics, they gain a genetic merit $5.00 greater than if sired by the poorer ram with a DPP of 1500.

So the extra return on this ram is $2,100 greater than the poorer ram with a DPP of 1500.

i.e. 420 progeny x $5 = $2,100

When considering the price of rams, paying even up to a $1000 more for the high index ram compared with the low index ram, will result in a net return of $1,100.

The real advantage is that the improved genetics, when included into a  breeders ewe flock, are cumulative with each generation. This is why buying top genetics is one of the best investments a sheep farmer can make. Research into the most profitable farmers shows that they always pay more for rams and bulls than average performing farmers.

When looking at various ram breeders to purchase from, always ask for their NZMW – DPP indexes to benchmark them between other breeders.


Make Accurate Comparisons

Also be careful to compare apples with apples. Look at the NZMW – DPP index, not a Dual Purpose Production Overall Index (DPO). The DPO measures sub-traits such as worm tolerance and eczema resistance. While these are important, their inclusion and how they are weighted affects the index value, so ensure you are benchmarking like with like.

“At Ashgrove we pride ourselves on having some of the leading genetics in the country based on across flock analysis and SIL Indexes. The stud has achieved national recognition as a finalist on two occasions now at the National Sheep Industry Awards. Coupled with Ashgrove’s FE Gold status, sheep farmers will struggle to find any higher genetic merit rams within Northland. And Ashgrove is positioned exceptionally well alongside other leading studs around the country.”


Below are brief explanations of the individual trait indexes that all add together to calculate the NZ Maternal Worth – Dual Purpose Production Index.


Dual Purpose Production now known as New Zealand Maternal Worth (NZMW)

Overall value expressed in cents for a ram formed by adding the indexes below (excluding Dual Purpose Meat). The term 'Dual Purpose' is used to describe maternal breeds such as Coopworths that are bred for meat and wool production. A ram with a 3000 NZMW or DPP index has $10 (1,000 cents) greater value  than a ram with a 2000 index. 100 of his daughters will receive half of his genetics therefore 50% of the $10 advantage. As breeding ewes will generate $500 more value than the daughters of a 2000 index ram.


Dual Purpose Reproduction.

This index shows in cents the fertility that a ewe expresses or a ram passes onto female progeny.


Dual Purpose Survival.

This index expresses in cents the mothering ability and vigour of lambs at birth that lead to lamb survival.


Dual Purpose Lamb Growth.

This index calculates in cents the economic value associated with growth.  The faster the rates of growth the higher the growth index. This index has a very high economic weighting as lamb weaning weights are a significant driver of profitability.


Dual Purpose Adult Size.

This index expresses the cost of having a large adult ewe which needs to be maintained, particularly through winter when feed is expensive. New Zealand's sheep flock has been improving it's growth genetics but this also results in ewes that mature into heavier sheep. Consequently most New Zealand flocks have negative indexes on DPA which detracts from their overall DPP economic index. High DPA sheep genetically have the potential to mature into big adult sheep if they are fed to their potential.


Dual Purpose Meat Yield.

This index expresses the value of meat yield. While many argue that meat yield is important it doesn't attract the same economic weighting as Growth because processors do not pay much of a premium on meat yield if at all.


Dual Purpose Wool.

This index expresses in cents the extra income derived from extra wool weight clipped off a sheep. While many have stopped selecting for wool it still makes a reasonable contribution to the overall DPP index, as a sheep that clips a heavier fleece still generates extra revenue than a low fleece weight sheep, particularly when the shearing cost is the same.