Understanding BLUP breeding values: Tips for navigating the numbers

We spoke to two experts to break down the numbers and correct some misconceptions surrounding breeding values.

What is BLUP?
BLUP is an acronym for “best linear unbiased prediction” and is a statistical method developed in the 1950s for animal breeding. It is used to estimate breeding values and genetic merit of a particular animal.
In short, the breeding values give an accurate indication of how a specific animal will breed. Since these values are based on herd-based performance testing, they are comparable across studs.

Typical traits reflected in Dohne Merino breeding values include:

BLUP BODY WEIGHT:

the predicted breeding value of an animal’s body weight

BLUP FLEECE WEIGHT:

the predicted breeding value of an animal’s fleece (i.e. whether it will produce less or more wool)

BLUP MICRON:

the predicted breeding value of an animal’s fibre thickness (i.e. whether it will produce finer or stronger wool)

Different breeding values can also be combined into General Merit – an overarching selection index that “summarises” the data, to show how desirable a particular animal is.

For many decades BLUP has been the method of choice in the breeding industry worldwide. This is still the case today, even with the latest developments based on the availability and inclusion of genetic (SNP) markers in genomic evaluations. “Of all information available, breeding values will always be the most accurate information to base selection on, especially when genomic information is also included in the predictions,” says Dr Mostert.

The breeder’s hand

Vaughan Collier, manager of the Dohne Merino Society of South Africa, agrees with Dr Mostert: “In the words of Stephan van der Westhuizen: ‘Breeding values are dangerously accurate.’ But the accuracy of your breeding values will depend on how accurately the breeder gathers and captures their data.”

Many of the factors that impact breeding values are directly in the hands of breeders, says Dr Mostert. These include: the heritability of the trait (the higher the heritability, the higher the correlation between the predicted and true breeding value of the animal), the accuracy and completeness of parent information, the size of the contemporary group in which the animal was measured, the number of measured relatives, and the especially measured progeny of the animal.

Don’t forget about the ewes

One of the most common misconceptions among farmers is that BLUP is only invaluable when selecting a stud sire, says Collier. “Nowadays it is becoming much more important to look at the fertility – and also the maternal ability – of your flock. Breeding values play a critically important role when it comes to selecting for these traits.”

It is also important to remember that the genetic potential for such traits – even for maternal ability – are evenly received from both parents. So, while a ram does not possess any maternal ability, it may have the potential to sire a ewe with great maternal ability, which will in turn be a strong breeder.

“The sires’ potential should therefore also be considered when improvement in fertility and maternal ability is included in the breeding goal,” says Dr Mostert.

Don’t be tripped up by GM 

Farmers should also be careful not to be blinded by numbers without understanding what they represent. For example, an impressive General Merit score.

“A selection index, like the General Merit, combines traits weighed according to their economic value in line with the selection objective of the Breed Society,” explains Dr Mostert.

Since GM represents various different traits, it can happen that an animal with a desirable selection index actually has inferior breeding values for certain traits due to others being exceptional. The inverse is also true: An animal with some stand-out traits can be overlooked, since their weak GM has been brought down by a few inferior traits.

In order to make sure that you properly understand the animal you’re selecting, it is always important to look at the individual breeding values that contribute to the GM before finalising your decision, says Dr Mostert. That way, the breeder can ensure that all traits are indeed better than the flock’s genetic levels, and that the next generation will benefit from the selected animal’s traits. 

“It is, however, also important that minimum cut-off limits for all contributing traits are in place when applying a selection index. This ensures that deterioration in traits does not occur due to other traits being exceptional,” she says. “At the end of the day, it’s all about balanced improvement – improvement in all traits in the next generation.”

Beyond the numbers

As in any industry, the numbers are important, but they rarely tell the whole story. Therefore, BLUP should not be the only consideration for farmers when selecting sheep.
“Functionality of an animal is just as important as the animal’s breeding values,” says Dr Mostert. “The animal should conform to breed standards, function efficiently with regards to movement, feed consumption, mating and lambing.”

Collier reminds farmers that the environment has a huge influence on the phenotype of an animal. “This must always be taken into consideration when animals are compared between different flocks.”

In turn, breeders should also consider whether the traits they are seeking for their flock will suit the physical environment in which they will live. It is vital that animals are able to adapt to environmental factors, like the climate – not only survive, but to breed and thrive.“It is always recommended to buy animals within the same environment where they are going to produce,” explains Dr Mostert. She also adds that semen quality, morphology and mobility of rams selected as sires for the next generation should always be checked, while screening for venereal diseases are of utmost importance.