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THE STATUS OF TRADITIONAL SCOTTISH ANIMAL BREEDS AND PLANT VARIETIES AND THE IMPLICATIONS FOR BIODIVERSITY
CHAPTER SIX: A SUMMARY OF THE SIZE AND COMPLEXITY OF GENETIC RESOURCES WITHIN ANIMAL BREEDS AND THE IMPACTS ON GENETIC DIVERSITY OF THEIR REDUCED USE
6.1 A genetic resource is an animal breed or crop variety in which genes or gene combinations of actual or potential value are found at high frequency. Generally these genes or gene combinations are linked with a visible phenotypic feature and there is usually supporting paperwork that certifies that a particular individual animal or plant belongs to a specified breed or variety. This is the definition that has applied in the past and which underpins the current relationships between genetic resources and the rest of agriculture. However it is conceivable that new advances in molecular and quantitative genetics will lead to a concept of genetic resources that is more individual-based than population-based. This section considers Scottish breeds as genetic resources within the traditional definition and suggests further investigations that would deepen our understanding of their place in world and national biodiversity.
Pedigree and breed structure
6.2 Formally, only pedigree or registered animals can be considered as genetic resources but in the commercial sector unregistered animals which conform to breed type are very important and probably in the majority. In practice, beef cattle and sheep tend to have a pyramidal breed structure with the herds and flocks at the apex being mainly composed of registered animals, which provide breeding stock to so-called multiplier herds and flocks, which themselves supply (usually unregistered) animals to the commercial sector. In dairy cattle the use of AI makes the multiplier sector superfluous and the practice of milk recording means that animals of high merit can be identified in the commercial sector for possible recruitment to the apex of the breed. Scottish breeds generally have strong and active breed societies but the costs of running these operations are high. Further research and development of registration management software, ideally designed to help in making breeding decisions, is needed.
Breed affinities
6.3 The histories of Scottish breeds have been well documented, especially over the last 200 years, and genetic studies have tended to confirm historical accounts of their breed affinities. Genetically they are distinct from English, Welsh and other north European breeds. Mitochondrial DNA studies of present-day Scottish cattle and fossil aurochsen (the wild ancestor of cattle that died out in Britain in the Bronze Age) have been taken to imply that incoming Neolithic herders mated their cattle with local aurochsen {Bailey, Richards, et al. 1996 ID: 4127}). This genetic distinctiveness could mean (1) Scottish breeds are a genetic resource that would be valuable for future farming needs that are currently not predictable; or (2) that there is potential for exploiting heterosis in crossbreeding them with other breeds.
6.4 Most of our knowledge of affinities among Scottish sheep breeds comes from historical studies and comparative work on fleeces (Ryder, 1968). Canadian microsatellite studies (Farid et al, 2000) show the South Country Cheviot and North Country Cheviot to be closely related. The Scottish Blackface appears quite close to north Continental European breeds. In cattle there has been more genetic work. Early studies of blood protein polymorphisms (Jamieson, 1966) revealed 'genetic affinities which cut across differences in the commercial purposes of distinct breeds … the Ayrshire, Galloway and Highland breeds show four transferrin genes in roughly similar proportions …'. Gene frequencies in the Aberdeen Angus were thought to reflect founder effects, with small numbers of important ancestors having strong influences on the breed. (Blott et al, 1998) found that microsatellite differences 'reflected geographical origin and common ancestry rather than function'. While the Ayrshire had affinities with the Friesian (this was also noted by (Kantanen et al, 2000), the Scottish breeds did form a fairly distinct subgroup, though even closely related breeds such as the Galloway and the Belted Galloway were distinct.
6.5 If the purpose of genetic conservation is to conserve the maximum amount of evolutionary history (Nee & May, 1997) and if this history is to be deduced from neutral marker genes then perhaps all the traditional Scottish cattle breeds have an equal claim. Further work is needed in two areas - firstly, on objective techniques of prioritisation for conservation (see for example (Ruane, 2000) and secondly on understanding the genetic affinities among Scottish sheep breeds.
Crossbreeding and introgression
6.6 Crossbreeding, when it is based on the maintenance of pure breeding populations which are mated for the production of the generation that is marketed commercially, is a highly efficient system for the sustained exploitation of heterosis (hybrid vigour).
6.7 Most Scottish sheep and cattle operations (the main exceptions being dairying and traditional hill sheep farming) are based on systematic crossbreeding whereby the animals that are sold for slaughter are genotypically a mixture of breeds. This may not be the case for all time; a move towards self-contained units which breed their own replacement females rather than buying them in, might be expected because stability of breeding groups is favoured on both welfare and disease limitation grounds.
6.8 Crossbreeding becomes grading-up when the crossbred animals are added to the breeding population; the effect is that genes from a different breed are moved into the breeding population. This is also known as introgression and is a rapid way of adapting a breed to meet new requirements although it can have harmful side effects. In the European dairy industry, the introgression of North American Holstein genes has increased milk yields but has also decreased fertility {Hoekstra, van der Lugt, et al. 1994 ID: 5425};{Lidauer & Mantysaari 1996 ID: 1195}; {Royal, Darwash, et al. 2000 ID: 8533}).
6.9 Most Scottish cattle breeds have been influenced by genes from overseas or from elsewhere in the UK; the number of Aberdeen Angus cows with no Canadian or New Zealand ancestry is now perhaps as low as 50 (Hart, 1999). Hill Scottish Blackface flocks have often used Swaledale rams (avowedly to improve maternal qualities) while the South Country Cheviot has received considerable input from the North Country Cheviot to increase body size. This is significant in that numerical status of a breed may not be the only important indicator of its conservation status - the degree of introgression it has undergone will also be important. There are no data on the extent or degree of these introgressions and a comparative study of these processes is needed.
Within-breed improvement
6.10 The main contemporary example of systematic within-breed improvement of a native Scottish breed is the SAC project to reduce carcass fat in the purebred Scottish Blackface (Conington et al, 1998). The campaign to rid the Galloway breed of the tibial hemimelia gene is another example, though rather different in that a specific gene has been vigorously selected against (p.325 of{Nicholas 1987 ID: 6049}). When there is a strong AI industry, as in dairy cattle, the genetic variation within a breed can be rapidly eroded by within-breed improvement for aspects of economic performance. A general survey of improvement programmes in Scottish breeds is needed.
Use of Scottish breeds in other countries
6.11 Sales abroad have of course been hit by BSE and by Foot and Mouth Disease, and scrapie control will be another constraint on exports of breeding sheep. Looking to the longer term, there is a strong interest in maintaining an international red and white dairy breed as an alternative to the Holstein (Ruane et al, 1999). However the Scottish Ayrshire is unlikely, because of its small population, to have much contribution to make to this process. Scottish beef cattle are appreciated for grazing management schemes aimed at promoting plant biodiversity and exploiting rough grazing, especially in the Netherlands and in Germany, but even without import restrictions this is unlikely to represent a big market. Generally the main market for Scottish breeding stock is likely to be within the UK and the Scottish breeds are probably to be seen as genetic resources within the UK context. A review of the numbers of animals of Scottish breeds outside the UK was outwith the scope of this study. A survey of such breeds should be considered and opportunities for the use of Scottish breeds outwith Scotland should be explored.
Specialisation
6.12 The most specialised Scottish breed is probably the Border Leicester which is used for production of crossbred lowland breeding sheep out of hill ewes. This is likely to be under threat from other crossing sires like the Bluefaced Leicester and from breeds which can combine the crossing and terminal sire roles, like the Rouge de l'Ouest. Information about the performance of such breeds and their crosses needs to be made available so their market niches can be developed.
6.13 The Aberdeen Angus seems to have strengthened its specialisation as a crossing sire for dairy cows, as suggested by the pattern of registrations. In the current herd book 40% of the 8269 registrations in 2000 were of males, implying a ready market for bulls outwith the breed. In contrast, in the Galloway only 8% of the 856 registrations in a similar period were of males. Thus, the Galloway is clearly specialised as a maternal or dam-line breed.
6.14 As is general in biological systems, specialisation poses threats as well as opportunities. A documented example of how a breed can change its specialisation comes from Southdown sheep (Hall, 1989). This breed used to be specialised for the production of purebred, light, early-maturing lamb from chalk grassland but from the 1950s this came to an end as chalk grasslands were taken over by cereals. Breeders then concentrated on producing specialised terminal sires (supplying about 2% of the ram market, for which only a small ewe population was sufficient). As that application has faded, the Southdown has now increased in numbers again, mainly as a purebred meat sheep kept in relatively small flocks which are not the main business of the farm.
6.15 Breed societies should attempt to keep and develop their specialised markets but must not lose their flexibility to respond to new market conditions. This is best done by encouraging new entrants to the breed as a dispersed system of relatively small flocks and herds is effective in maintaining genetic variation. Breed societies should not dismiss the advantages of association with the Rare Breeds Survival Trust, though there may be public relations issues. There should also be systematic programmes of cryoconservation (freezing of semen and embryos), preferably with a regeneration protocol. This protocol would reduce the risks of stored material proving unusable in the future because of new, unanticipated veterinary restrictions, and would involve the regeneration of animals from stored material, and the storage of semen and embryos therefrom. Research is needed on the most effective way of operating such programmes.
Conservation of genetic variation
6.16 A strongly pyramidal breed structure (in which only a few herds or flocks supply sires for use elsewhere in the breed) is more conducive to genetic improvement (and thus antagonistic to conservation of genetic variation) than a more 'democratic' structure in which a high proportion of herds or flocks supply sires. In British rare and minority sheep (Hall, 1986; Hall, 1989) the proportion of flocks that supply sires is between 29 and 37%. This relatively high proportion means that the breeds are not dominated by the breeding goals of a small number of breeders. In Galloway cattle, which are declining in numbers, the average proportion between 1997 and 2000 was 23%, which implies a relatively pyramidal structure. In England, the Lincoln Red has about one third of the annual registrations of the Galloway and in 1997 and 1998, 60% and 41% of herds respectively supplied the sires. In at least some minority Scottish breeds, therefore, a decline in total numbers may be accompanied by a breed structure which could be inimical to genetic conservation. Further research is urgently needed on the nature and genetic consequences of the population structures of the Scottish breeds.
Institutional strengthening
6.17 Under the Convention on Biodiversity the UK Government has a responsibility for the conservation of agricultural genetic resources. One way of discharging this responsibility in an economical manner would be for Government to support the breed societies. Breed societies were not established to maintain inventories and are not organised in such a way as to facilitate this. Databases on livestock do not map onto each other in ways which permit the status of breeds to be monitored. Government should consider making funding available for the effective management and cataloguing of genetic resources.
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