It may be that some of the Society’s members ask why we are not just a simple private club, but a Company, a Charity and a Defra Recognised Breed Society?
Being a Company sets standards for accountability, transparency financial reporting and gives members protection and a legally sound way to have oversight of their Society.
Being a Charity gives significant tax relief in return for the public benefit which is: ‘To promote for the benefit of the public the conservation, protection and improvement of the natural environment by promoting biological diversity through the promotion and registration of Southdown sheep.’
Being a Defra Recognised Breed Society allows the Society to control imports and exports, and prevents duplicate breed societies being created.
So how does the Society show it is fulfilling its obligations that bring these benefits, and so protect the Southdown breed. We do report annually to the Charity Commission, but clearly they are not experts on the breeding of sheep!
But if they ever asked we could remind them that to become a Defra officially recognised breed society, we must:
keep a flock book
create a breeding programme for our breed
have legal status, for example, be a limited company or registered charity
employ qualified staff
have policies for managing complaints and data governance
have rules of association that govern membership
be able to check the recording pedigrees of the breeding animals
have enough breeding animals in the UK for healthy population growth
be able to generate and use data collected on breeding animals
How the Society meets these requirements has been submitted to Defra and has been approved by them.
You will notice our Charitable objectives require us to ‘promote biological diversity’ and Defra requires we ‘have enough breeding animals in the UK for healthy population growth’.
So each year the Society reports numbers to Defra, and also to the RBST for its Watchlist. But it not just the numbers of males, females, offspring and breeding animals that is important. You could have a very large group of breeding animals that are so closely related that genetic diversity is reduced.
Such inbreeding is bad news for a breed, since mating of closely related individuals can lead to inbreeding depression which is defined as reduced fitness of the offspring including loss of productivity, greater susceptibility to disease, inability to adapt to changing environments and increased pregnancy and neonatal losses.
Genetic diversity is a key component of biological diversity that is a requirement to promote for a (genetically) healthy population. Genetic diversity in UK breeds can be assessed by the effective population size, which accounts for the total number of animals in a population and the relative numbers of sires and dams (male and female parents). A low effective population size signifies a greater likelihood of inbreeding and risk of loss of genetic diversity.
So, what is a low effective population size? If around 100, the rate of loss of genetic diversity is approximately 4% in ten generations, when it falls to 50, loss of genetic diversity greatly increases to approximately 10% in ten generations,
At an effective population size of 50 or below, a population risks falling into what is aptly named an ‘extinction vortex’. This is where small populations experience inbreeding, reducing fitness with erosion of genetic variation and reduced rates of future adaptation which in turn leads to further genetic erosion until the population is highly vulnerable to extinction.
When applied to breeds, say of sheep, that erosion does not lead to loss of the species. but it does lead to loss of the breed as there is simply not enough genetic diversity to healthily maintain its breed characteristics.
The average effective population size of native British sheep breeds is currently around 350, with Poll Dorset, Ryeland and Lleyn with effective population sizes in the 2-3,000s, and breeds such as Lincoln Longwood and North Ronaldsay just below 200.
For 2023 the Society reported numbers that led to a calculated effective population size of 1060. This is good news, and especially as the Southdown effective population size has climbed from a number of around 600 at the turn of the century.
These numbers show good stewardship of the breed by the Society’s members and its Trustees, but it is important not to be complacent. One straightforward component of limiting loss of genetic diversity it to ensure a wide range of males are used for breeding.
However, the Society also has a hidden asset that might surprise members. There have always been debates on traditional and various imported types within the breed, and is not just a recent phenomenon.
If you go back to ‘The Southdown Sheep’ book published in 1936 by the Society and you will find sections on Southdowns in France, in Canada, in New Zealand, in Australia, California and the USA.
The surprise is that such ‘sub-populations’ significantly increase the breed’s genetic diversity as they maintain elements of discreet genetic diversity with those sub-populations.
So, rather than just being a source of debate, or even friction at times, these sub-populations within our breed greatly contribute to our obligations to promote biological diversity of the overall Southdown breed.
Professor Tim Morris
