Close bloodlines - how close is too close?

Liz · Post by **Liz** » Thu Sep 23, 2004 11:17 am

I am hoping to borrow a bull for my few cows. On checking his pedigree I see that the Sire of one of my cows is the same animal as the Great Grand Sire of the proposed bull. Is this likely to be a problem? If so, what sort of problem?

Duncan MacIntyre · Post by **Duncan MacIntyre** » Thu Sep 23, 2004 1:34 pm

Unless the common ancestor is thought to carry some undesireable condition, e g wry tail, or twisted front legs, there is not the slightest worry with this proposed mating as far as I can see. At most the resultant calf will inherit 25% of its genes from its maternal grandfather, and 6.25% from its great great grandfather being the same animal - a total of 32.25% from that one animal.

Duncan

Jo Kemp · Post by **Jo Kemp** » Thu Sep 23, 2004 4:41 pm

Hmmm 'how close is too close though?
What about half brother & half sister out of a very good cow and totally unrelated sires? Would this not be 'line breeding which is done by breeders of note with great success.

Duncan MacIntyre · Post by **Duncan MacIntyre** » Thu Sep 23, 2004 9:54 pm

Hello Jo,
I did not really want to get straight into inbreeding too deeply from Liz's question, but yes half siblings are frequently mated by breeders wishing to follow a particular line. Inbreeding can be a valuable tool to bring out particular characteristics, but as it tends to reveal any recessive genes bad things can show up as well as good. So the brave breeder who does it must accept that there may be poor animals or ones with faults as well and they will have to be culled or used for beef. But for beginners, especially with only a few cows, it is not necessarily the way to go as it can lead to disappointment as well as success.
My own goal at present is to breed dexters which do not carry the bulldog gene but are about the same height as we expect of short-legged types today. For this I am at present into half brother and sister matings and the next generation of heifers will go back to the old bull as long as nothing nasty shows up. I might not succeed, of course - that is a risk I am willing to take but would not suggest that others should necessarily do the same.

Duncan