Multibreed EBVs

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Introduction to the first Australian Multibreed EBVs

In BREEDPLAN, all breeds currently have their own bases, hence within-breed EBVs of one breed cannot be directly compared with EBVs of another breed. Many breeders have sought an improvement in this situation, in effect asking for ‘Multibreed EBVs’ or ways to put breeds onto a common base.

With Meat and Livestock Australia (MLA) funding support, work carried out early in 2003 at the Animal Genetics and Breeding Unit (AGBU) has allowed the development of the first adjustment table for BREEDPLAN Multibreed EBVs. The AGBU geneticists used:

This has produced sufficiently accurate comparisons of four breeds for some birth , growth and carcase weight traits. It was hoped that conversions for more breeds and traits would be possible, but the required accuracy was unfortunately not available from current data. This is, however, a sound start on which to add further traits/breeds as new data becomes available.

Multibreed EBV adjustment table

An adjustment table based on the above data is AGBU’s initial move towards development of full Multibreed BREEDPLAN EBVs. This table gives adjustment factors to add to within-breed EBVs, making them comparable across breeds. Table 1 gives these adjustments for:

  • gestation length
  • birthweight
  • the growth traits (200-day weight, 400-day weight and 600-day weight)
  • carcase weight

for the following breeds:

  • Angus
  • Poll/Hereford
  • Limousin
  • Simmental.

Currently, it is only the above EBVs that can be compared across these four breeds. Further research is underway to add more traits/breeds to this table and to develop methodology for the preferred outcome of Multibreed EBVs by analysing combined breed datasets.

Table 1. Multibreed EBV adjustment table (March 2003)
To produce Multibreed EBVs, add the amount listed in this table to an animal’s existing within-breed BREEDPLAN EBV for each trait. Note: This is not a breed comparison table (see Tables 2–5).
 Trait
Gest. length Birth-weight 200-day weight 400-day weight 600-day weight Carcase weight
Angus 0 0 0 0 0 0
Poll/Hereford 1.1 2.8 9 21 16 8
Limousin 9.2 6.4 13 25 17 20
Simmental 6.4 8.7 31 63 71 n/a

n/a — Insufficient data at present.

Using Table 1 — Example

To compare: an Angus bull that has a birthweight EBV from Angus BREEDPLAN
with: a Limousin bull that has a birthweight EBV from Limousin BREEDPLAN
you would: add 0 (from Table 1) to the Angus EBV
and: add 6.4 to the Limousin EBV.

This is further illustrated in Tables 2–5 below, where average within-breed EBVs for 2001-born animals have been converted to Multibreed EBVs by this method.

Note the date, March 2003, in the heading of Table 1. Just as EBVs change over time, so too do the adjustments, so check that you have the most recent adjustment table .

Examples of Multibreed EBVs

Tables 2–5 show the results when the adjustments from Table 1 are added to breed average within-breed BREEDPLAN EBVs for 2001-born animals:

Table 2. Gestation length
Breed Gestation length EBV
Breed average EBV Adjustment factor Multibreed EBV
Angus –1.3 +0.0 –1.3
Poll/Hereford 0.0 +1.1 +1.1
Limousin –0.5 +9.2 +8.7
Simmental –0.2 +6.4 +6.2
Table 3. Birthweight
Breed Birthweight EBV
Breed average EBV Adjustment factor Multibreed EBV
Angus 4.0 +0.0 4.0
Poll/Hereford 4.0 +2.8 6.8
Limousin 1.3 +6.4 7.7
Simmental 1.7 +8.7 10.4
Table 4. 400-day weight
Breed 400-day weight EBV
Breed average EBV Adjustment factor Multibreed EBV
Angus 52 +0 52
Poll/Hereford 32 +21 53
Limousin 19 +25 44
Simmental 23 +63 86
Table 5. Carcase weight
Breed Carcase weight EBV
Breed average EBV Adjustment factor Multibreed EBV
Angus 33 +0 33
Poll/Hereford 27 +8 35
Limousin 16 +20 36
Simmental n/a n/a n/a

Using Multibreed EBVs

Some of the uses for Multibreed EBVs are as follows:

  • Stud breeders may be interested to compare their stock with other breeds and perhaps review selection priorities.
  • Crossbreeders and composite developers will be able to better select breeds and sires to use . Note that in crossbreeding situations , the Multibreed EBVs hold only if the bulls being compared are to be mated to cows that are of the same breed as each other, unrelated to the breeds of the bulls.

Example

Breed average 2001 drop Simmental and Angus bulls are to be mated to Shorthorn cows. From Table 3, we would expect the Simmental × Shorthorn calves to be 3.2 kg heavier at birth than the Angus × Shorthorn calves (3.2 kg is half the difference between the Multibreed birthweight EBVs of Simmental and Angus bulls, which are 10.4 and 4.0 respectively in Table 3). At 400 days, the Simmental crosses are predicted to be 17 kg heavier [(86 – 52) ÷ 2] from Table 4.

  • Another reason for using Multibreed EBVs is to find the equivalent within-breed EBVs for a bull of another breed.

Example

An Angus bull with a within-breed birthweight EBV of 5.0 would produce calves of the same birthweight as a Hereford bull with a within-breed EBV of 2.2 kg.

That is, 5.0 – 2.8 = 2.2
The figure of 2.8 is the adjustment for birthweight for Hereford bulls, obtained from Table 1.

Similarly, an Angus bull with a within-breed carcase weight EBV of +30 would produce the same carcase weight in 650-day-old steers as would a Limousin bull with its within-breed carcase weight EBV of +10.

That is, 30 – 20 = 10.
The figure of 20 is the adjustment for carcase weight for Limousin bulls, obtained from Table 1.

Methodology used to develop the table

Data for the adjustment tables came from the following projects:

  • The MLA-supported Victorian Multibreed project used 22 sires from each of the Angus, Hereford, Limousin and Simmental breeds, mated to Angus and Hereford cows in Southern Australia in 1997 and 1998, across 19 herds. All sires had BREEDPLAN EBVs and represented a spread in the 400-day weight EBV of their breed. Sires with extreme birthweight EBVs were not used. The number of calves generated was 2566, and their management and performance were recorded for numerous traits.
  • The Beef CRC design involved 9 sire breeds joined to Brahman cows in 1993–95 in 2 herds in subtropical central Queensland. Progeny of the 8 sire breeds with BREEDPLAN analyses were considered in this work: Brahman, Belmont Red, Santa Gertrudis, Angus, Hereford, Shorthorn, Charolais and Limousin. Calves were generated by artificial insemination (AI) and natural mating, and at weaning they were allocated to ‘grow-out treatment’ groups, involving market weight and finishing regimes. The number of sires per breed ranged from 8 to 15. There were 7 sires in common across the two projects.

This data was used by the Animal Genetics and Breeding Unit (AGBU) as follows:

  1. The data was adjusted to the BREEDPLAN definitions.
  2. Environmental effects were accounted for.
  3. The sire breed differences for each trait were then estimated.
  4. The average BREEDPLAN EBVs of the sires used in the projects for each trait were then obtained.
  5. The two pieces of information in steps 3 and 4 above were used to compute adjustment factors to add to within-breed EBVs to make them comparable across breeds.

Important notes

  • There are currently conversions only for those traits listed in Table 1; that is, it is not yet possible to compare calving ease, milk and carcase EBVs across breeds. Therefore, when using current Multibreed EBVs, it is important not to ignore the EBVs for the other very important traits.
  • EBVs are not absolutes. They give a best possible estimate of the expected differences between animals for a particular trait. The same applies for Multibreed EBVs, which can be used to predict the expected difference in the progeny of animals from different breeds. There is, however, an additional consideration with Multibreed EBVs, as the expected difference is also dependent on the cow breed used (crosses generate hybrid vigour in the progeny). here are a couple of scenarios that should be explained:
    • If we use the Multibreed EBVs from two bulls, an Angus and a Hereford, both joined to a third breed, for example Shorthorn cows, then hybrid vigour is expected to be similar and therefore the EBVs predict the difference in the progeny.
    • However, if the cow breed is Angus, then the Angus × Angus progeny would exhibit no hybrid vigour but the Hereford × Angus progeny would. Therefore, in this case the expected progeny difference predicted by the Multibreed EBVs would need to include an estimate of hybrid vigour.
  • Adjustments in Table 1 are estimates and therefore may change with additional breed comparison data or as the breeds continue genetic change at varying rates. The accuracy of a Multibreed EBV is therefore lower than the accuracy of a within-breed EBV.

About the authors

David Johnston is a Research Geneticist with the Animal Genetics and Breeding Unit (AGBU), a joint Institute of NSW Agriculture and the University of New England. AGBU receives considerable funding for its BREEDPLAN research and development from Meat and Livestock Australia (MLA). BREEDPLAN and GROUP BREEDPLAN results are calculated using software developed by AGBU.

Brian Sundstrom is Cattle Breeding Coordinator with NSW Agriculture. Part of his role involves Technical Specialist and Advisory work with BREEDPLAN from an office at the Agricultural Business Research Institute (ABRI). His other major extension role is with the Beef Cooperative Research Centre.