Ans: The Gene Pool is only reduced if the 5 Star bulls are all inter-related.
Two tools that a breed could exploit more to prevent the gene pool getting tight are ‘Gene Ireland’ and ‘Genomics’.
Taking the Limousin breed as an example, in 2017 there were 9,294 pedigree limousin calves born. 66% of these were sired by 236 different AI Sires. The remaining calves were sired by 841 different Stockbulls. Granted there are well used sire lines across those AI Sires and Stockbulls however Limousin breeders appear to be already using a wide range of pedigree bulls as sires of sons.
That said ‘Gene Ireland’ and ‘Genomics’ could be exploited by all breeds more to make sure that the gene pool does not tighten.
Gene Ireland: This is a Progeny test programme where the Breed Society has a direct input into the bulls that are purchased for progeny testing. It is a program that is run in conjunction with Dovea, NCBC and all the Breed Societies. ICBF purchases the bull’s – enough semen is taken off them to get them progeny tested in commercial herds and then for pedigree matings afterwards. The beauty of such a programme is the control that it brings a pedigree breed in terms of not allowing bulls from any one bloodline to get continuously picked thus leading to a smaller gene pool.
Genomics: ‘Outcross’ bulls by their very nature will have low reliabilities because they have very few if any relatives in the system here that would lift their reliability % figures. Up to now the only way such bull’s reliabilities could have increased is if foreign breeding values were available. France & the UK do provide such data however if the bull has a low reliability % and maybe doesn’t even have many progeny records in its country of origin, then that foreign data might not have a huge effect on its Irish €uro-Stars. Whereas genotyping the bull gets around all of that and analyses each bull for the same number of traits.
A prime example of the effect that genotyping can have on an ‘outcross’ bull is the polled Limousin AI Sire ‘Tigris’. He is pretty much a complete outcross pedigree to the Irish Limousin population (except for ‘ULE’ on his dam’s side). In August 2016 his reliability % figure for the ‘Replacement Index’ was 22% and for the ‘Terminal Index’ was 43%. A straw of his was then genotyped before the December ’16 run and his reliability % figures rose to 42% and 54% respectively. Genotyping revealed that he was not getting as much credit as he deserved for his ‘Replacement Index’ in particular, hence its increase from €31 to €91. So, Genotyping has meant that this outcross bull which could widen the gene pool of the Limousin breed could then be used by Breeders with greater confidence than was the case before he was genotyped.