Australian Sheep Breeding Values

Defining your breeding objective is the first step toward building a more productive flock. From there, Australian Sheep Breeding Values (ASBVs) provide a trusted, data-driven framework to guide selection decisions based on traits that matter most to your enterprise.

What are ASBVs

Australian Sheep Breeding Values (ASBVs) are estimated breeding values used to assess and compare the genetic merit of sheep in Australia. Covering a wide range of economically significant characteristics—such as growth, fertility, carcass quality, and wool traits—ASBVs give breeders an objective tool to complement visual assessment and make more informed, goal-driven selection decisions.

An animal’s observed traits—such as growth rate, fleece weight, or fertility—are influenced by both its genetics and the environment in which it was raised. Factors like nutrition, seasonal variation, or birth type (single or twin) can significantly affect performance. ASBVs account for these non-genetic influences, allowing animals to be compared on a consistent genetic basis, regardless of their management or rearing conditions.

ASBVs are available for a wide range of traits that directly influence flock performance and enterprise profitability. These include genetic indicators for:

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growth traits,

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carcase and eating quality traits,

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To help simplify animal evaluation and accelerate breeding progress toward specific production goals, the ASBV system offers selection indexes. These indexes combine multiple individual traits into a single numerical value that reflects an animal’s overall genetic merit for a defined production system.

Using selection indexes allows to:

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compare animals across multiple traits at once,

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make decisions based on economically relevant priorities,

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drive faster and more targeted genetic improvement.

The choice of index should always reflect the breeding objectives of your operation — whether focused on prime lamb production, wool quality, or balanced performance.

How to interpret ASBVs

ASBVs are expressed relative to a baseline of zero, which corresponds to the average performance of animals born in 1990 — the reference population that formed the foundation of the Sheep Genetics database.

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Positive values indicate a higher expression of the trait compared to this historical average.

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Negative values indicate a lower expression.

A lower or a negative ASBV does not necessarily mean inferior performance. For some traits — particularly health indicators such as WEC (worm egg count) or LDAG (dag score) — lower values are desirable.

To assess how strong or weak a value truly is, it’s essential to compare ASBVs to current industry percentiles. These benchmarks help place individual animals in the broader genetic context.

We provide percentile rankings in our catalogue to support informed, data-driven selection decisions.

TOP 5

TOP 10

TOP 20

Most ASBVs are reported with an age stage prefix, indicating the point in an animal’s life at which the trait is expressed or measured. Selecting traits with age stages aligned to your production targets ensures greater relevance and accuracy in selection decisions.

For example, in systems where lambs are finished at approximately 7 months of age, Post Weaning Weight (PWT) may be a key indicator of performance.

Trait abbreviations typically begin with a letter corresponding to the age stage — for instance, BWT refers to birth weight.

Age stage

Stage code

Definition

Birth

B

Birth to 24 hours of age

Weaning

W

7–16 weeks

Post weaning

P

4–10 months

Yearling

Y

10–13 months

Hogget

H

13–18 months

Adult

A

18 months or older

Some traits are reported as early (E) (<4 months) or late (L) (>4 month) age stages.

Growth traits

Trait

Description

Units

Stages

Weight (WT)

Describes the genetic difference between animals in body weight

kgs

B, W, P, Y, H, A

Maternal Weaning Weight (MWWT)

Describes the difference in maternal genetic effects on the progeny’s weight. This includes the ewe's potential to provide a better maternal environment including milk production

kgs

W

Carcase and eating quality traits

Trait

Description

Units

Stages

FAT
Fat Depth

Describes the genetic difference between animals in fat depth (FAT), corrected for liveweight

mm

P, Y, H

EMD
Eye Muscle Depth

Describes the genetic difference between animals in eye muscle depth corrected for liveweight

mm

P, Y, H

IMF
Intramuscular fat

Describes the genetic difference between animals in intra-muscular fat which has the visual component known as marbling

%

No stage code — refers to carcase trait

SHEARF5
Shear force

Describes the genetic difference between animals in shear force at 5 days of carcase aging

Nm

P, Y, H

LMY
Lean Meat Yield

Describes the genetic difference between animals in lean meat yield

Percentage (%)

P, Y, H

DRESS
Dress percentage

Describes the genetic difference between animals in dressing percentage

Percentage (%)

No stage code — refers to carcase trait

CWT
Carcase weight

Describes the genetic difference between animals in carcase weight

kg

No stage code — refers to carcase trait

CEMD
Carcase eye muscle depth

Describes the genetic difference between animals in carcase eye muscle depth

mm

No stage code — refers to carcase trait

CFAT
Carcase fat depth

Describes the genetic differences between animals in tissue depth at the GR site

mm

No stage code — refers to carcase trait

CCFAT
C-site carcase fat depth

Describes the genetic differences between animals in fat depth at the C-site

mm

No stage code — refers to carcase trait

Wool traits

Trait

Description

Units

Stages

CFW
Clean Fleece Weight

Describes the genetic difference between animals in clean fleece weight

Percentage (%)

P, Y, H, A

GFW
Greasy Fleece Weight

Describes the genetic difference between animals in greasy fleece weight

Percentage (%)

P, Y, H, A

FD
Fibre Diameter

Describes the genetic difference between animals for fibre diameter

Micron (µm)

P, Y, H, A

DCV
Fibre Diameter Coefficient of Variation

Describes the genetic difference between animals for fibre diameter coefficient of variation

Percentage (%)

P, Y, H, A

SS
Staple Strength

Describes the genetic difference between animals for staple strength

Newtons per kilotex (N/Kt)

P, Y, H, A

SL
Staple Length

Describes the genetic difference between animals for staple strength

mm

P, Y, H, A

CUR
Curvature

Describes the genetic difference between animals for fibre curvature

Degrees per millimetre

P, Y, H, A

LCHAR
Late Wool Character

Describes the genetic difference between animals in wool character (CHAR)

Visual score

LCOL
Late Wool Colour

Describes the genetic difference between animals for the amount of colour in the wool staple. LCOL is expressed as a score

Visual score

LFROT
Late Fleece Rot

Describes the genetic difference between animals for the amount of fleece rot in the wool staple

Visual score

Reproduction traits

Trait

Description

Units

NLB
Number of Lambs Born

Describes the genetic difference between animals for the number of lambs born at each lambing opportunity

Percentage (%)

NLW
Number of Lambs Weaned

Describes the genetic difference between animals for the number of lambs weaned at each lambing opportunity

Percentage (%)

CON
Conception

Describes the genetic difference between animals for conception. Did the ewe conceive? Sires with higher CON will produce daughters which have a higher conception rate

Number of lambs

LS
Litter size

Describes the genetic difference between animals for litter size. How many lambs were born? Sires with higher LS will produce daughters that give birth to more lambs

Number of lambs

ERA
Ewe rearing ability

Describes the genetic difference between animals for rearing ability. How successfully did the ewe rear her litter? Sires with higher ERA will produce daughters which rear more of their litter

Number of lambs

MBS
Maternal behaviour score

Describes the genetic difference between animals for maternal behaviour. How far the ewe moves from the birth site when her lambs are being tagged? Sires with lower MBS will produce daughters that have better maternal behaviour, as they stay close to their lamb during the first 24 hours of life

Number of lambs

SC
Scrotal Circumference

Describes the genetic difference between animals for scrotal circumference. This is expressed in centimetres (cm)

P, Y, H

Health traits

Trait

Description

Units

WEC
Worm Egg Count

Describes the genetic difference between animals in worm egg count. This trait is measured at P, Y, H and A.

EBWR
Early Breech Wrinkle

Describes the genetic difference between animals in breech wrinkle

Score

LDAG
Late Dag

Describes the genetic difference between animals in dag

Score

EBCOV
Early Breech Cover

Describes the genetic difference between animals in breech cover

Score

LE_DIR
Lambing Ease Direct

Estimates the genetic difference between animals in the lambing ease of their progeny, for example, the ability of a sire’s lambs to be born unassisted. Higher, more positive ASBVs for this trait are more favourable. In a cross-breeding program where rams are being used as terminal sires and all progeny are being slaughtered, the LE DIR ASBV is the appropriate trait to use

Percentage of unassisted lambings (%)

LE_DTR
Lambing Ease Daughters

Estimates the genetic difference between animals in the lambing ease of their daughters, for example the ability of a sire’s daughters to lamb without assistance. Higher, more positive ASBVs for this trait are more favourable. Where rams are being used to breed replacement ewes, it is important to include both LE DIR and LE DTR in the selection process. As the LE DIR ASBV describes how easily his lambs will born and the LE DTR ASBV describes how easily his daughters will have lambs

Percentage of unassisted lambings (%)

GL_DIR
Gestation length

Describes the genetic difference between animals in gestation length. A lower, more negative ASBV indicates a shorter gestation length, which is generally associated with improved lambing ease. It is important to note that this is a trait that needs to be optimised as extreme ASBVs at both ends of the scale can have a detrimental effect on lamb survival. Very long gestation lengths can cause additional dystocia problems as lambs gain weight very rapidly towards the end of pregnancy. Conversely, very short gestation lengths may result in small lambs that do not have the energy reserves to withstand adverse weather conditions

Days

CS
Condition score

The condition of the ewe at joining. It describes the genetic difference between animals for condition score as adults. This trait is current in its research phase, as more data is collected by industry, and the genetic parameters are finalised for this trait

Score

FR
Foot rot

Footrot (FR) describes the genetic difference between animals for their susceptibility to footrot. This trait is currently only available to New Zealand Merino breeders

Score

Other traits

Trait

Description

Units

POLL
Poll-Horn Genomic Test

Describes the genes the animal has for being polled or horned

PP, PH or HH

BREED
Breed Composition

Describes the breed proportion of each animal

Percent between 0 and 1

INBREEDING
Inbreeding

Describes the inbreeding percentage for each animal

Percent between 0 and 1

Terminal selection indexes

Index

Primary focus

Traits included

TCP
Terminal Carcase Production

Lean meat yield with modest eating quality

PWT, PEMD, PFAT, DRESS, LMY, IMF, SHEARF5, LE

EQ
Eating Quality

High eating quality + modest meat yield

PWT, PEMD, PFAT, DRESS, LMY, IMF, SHEARF5, LE

LEQ
Lamb Eating Quality

Eating quality + parasite resistance

All EQ traits + WEC

Maternal selection indexes

Index

Primary focus

Traits included

BLX
Border Leicester Cross

Growth and reproduction in Merino crossbreeding systems

BWT, PWT, PEMD, AWT, NLW

MCP
Maternal Carcase Production

Growth, carcase and reproduction in self-replacing systems

PWT, PEMD, PFAT, AWT, NLW

MCP+
Maternal Carcase Production Plus

MCP + fleece weight and parasite resistance

PWT, PEMD, PFAT, AWT, NLW, YCFW, YFD, WEC

MWP+
Maternal Wool Production Plus

Wool production + growth, carcase and reproduction

YCFW, YFD, PWT, PEMD, PFAT, AWT, NLW, WEC

Summary

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Australian Sheep Breeding Values (ASBVs) enable objective comparison of genetic merit between rams.

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Rams pass on half of the genetic material to their offspring, and because each sire can produce a large number of progeny, they represent the most powerful lever for accelerating flock improvement.

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While ASBVs are expressed relative to a baseline of zero, effective use requires comparing an animal’s values against percentile bands to understand how it ranks within the industry.

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ASBVs are presented with an accuracy figure, which reflects how closely the estimate is expected to align with the animal’s actual breeding value. Greater accuracy comes from more performance records and progeny data.

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ASBVs include a prefix that indicates the age or stage of life at which the trait was measured. For example, BWT refers to birth weight.

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Indexes combine multiple traits into a single value that reflects an animal’s overall genetic suitability for a specific production system.

FAQ

What are ASBVs used for?

Australian Sheep Breeding Values (ASBVs) are used to compare the genetic potential of animals for economically important traits, helping producers make informed breeding and selection decisions.

How are ASBVs calculated?

ASBVs are calculated using performance data, pedigree, and genomic information from across the national flock. These values estimate the genetic merit of an animal for specific traits.

Can ASBVs predict lamb performance?

Yes — because each parent contributes half of the genetic material to their offspring, ASBVs are a powerful tool for predicting the performance of future generations.

What does a negative ASBV mean?

A negative ASBV does not necessarily indicate poor performance. For some traits — such as Worm Egg Count (WEC) or Dag Score (LDAG) — lower values are actually desirable.

Are ASBVs the same as selection indexes?

Not exactly. ASBVs represent individual traits, while selection indexes combine multiple traits into a single value aligned with specific production goals.

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