Genetics for composite sheep opens new doors
| IMPACT OF HYBRID VIGOUR ON FLOCK PERFORMANCE | |
| Hybrid vigour in the crossbred lamb | |
| Trait | Hybrid vigour [%] |
| Weaning weight | 5.0 |
| Yearling weight | 5.2 |
| Lamb survival | 9.8 |
| Lambs reared per ewe | 15.2 |
| Weight of lamb weaned per ewe | 17.2 |
| Hybrid vigour in the crossbred ewe | |
| Fertility | 8.7 |
| Prolificacy | 3.2 |
| Lamb survival | 2.7 |
| Lambs reared per ewe | 14.7 |
| Weight of lamb weaned per ewe | 18.0 |
In the past breeding stock has tended to be either purebred or a traditional first cross between two pure breeds. In the future will breeders seek to create crossbred, composite breeding lines combining the attributes of different breeds to produce genetically superior stock – as has been done in the pig and poultry sectors?
In the UK the creation of composite strains of sheep is far from new, but few – with the exception of the Meatlinc – have achieved commercial success because they have been poorly marketed and too much emphasis has been placed on appearance, by both breeder and buyer.
This doesn’t mean a British composite wouldn’t be readily accepted today, as commercial producers become more technically aware and responsive to change.
There is one big difference between modern composite production and that of the past. Modern composite flocks tend to run an open nucleus, enabling new genetics to be infused into the flock at any point. This has a number of advantages. High levels of hybrid vigour can be locked into the breeding line, enhancing traits of low heritability, such as health, fitness and reproductive performance.
Faster rates
Faster rates of genetic gain can be achieved, as elite genetics are not simply sourced within the breed, but across the species. Open breeding programmes allow the integration of new genetics, including significant genes, from other breeds, which enable a breeding line to carve out a unique genetic niche.
However, composite breeding programmes tend to be more complex and larger breeding flocks are required to allow for the testing of new genetics – and inevitable wastage.
Breeding potential can be more difficult to evaluate, because of the effects of hybrid vigour. The biggest challenge is due to variation in appearance that arises when a composite is produced. Composite breeders must improve their marketing skills to avoid discrimination and promote the benefits of a visually less attractive animal, because marketing the mongrel is a skill in its own right.
Composite breeding strategies are clearly an appropriate breeding solution for enhancing maternal performance, because of the massive impact hybrid vigour has on maternal traits of high economic value, but low heritability such as fertility and longevity (see table).
Succesful
By contrast British terminal sire breeders have been extremely successful in enhancing carcass attributes using EBV-based within breed selection. It is likely that only when ram longevity, lamb vigour and lamb survival start to suffer a composite approach will become a more attractive proposition. The success of composite terminal sires will be as much to do with the failure of purebred breeders to address issues of commercial concern, as it is their genetic superiority.
British ram breeders looking to adopt composite breeding strategies have two options they can import genetics from overseas or create their own breeding lines using British genetics.
The advantage of importing overseas genetics is that breeders will gain access to an established, stabilised, large scale breeding programme, with potential marketing support from an established breeding company. However, overseas breeding goals will differ to those in the UK and relative levels of performance are unknown.
British breeders creating new composite breeding lines based on UK genetics have complete control over their breeding programme, but it will take time to develop and market the newly created composite strains.
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