A tricky player in the genetics of coloured…
We received the following question in relation to breeding specific colours into a breed that does not have it naturally, and we thought other people might find it interesting:
“I am trying to develop a spotted Babydoll. I have spotted Dorper ewes with an off white Babydoll ram. This produced some 50% spotted/piebald ewe lambs. Should I use agouti to keep colour or do I need to find another ram that is from Dorper origin that may carry the spotting gene?
I really want to get to 100% Babydoll but we don’t have spotted available yet, only brown. By crossing them with each other I am not increasing my %.
How can I get my spots without a spotted Babydoll ram?”
Here is our response to the question:
As far as we know spots don’t occur naturally in Babydolls in Australia – while there is some evidence that Southdowns (Babydolls are Southdowns) had spots originally, this trait has largely been bred out of them and the only references we could find to spotted Babydolls were in the US. So what would be the simplest avenue – finding someone who’s breeding them and using those bloodlines – is probably not an option. How to get them using other breeds would depend on your goals.
Dorpers are Extension dominant (Ed) and their markings are also a modification of HST (head,socks, tail) spotting. This means that they will pass on their colour even when crossed over white sheep. When they are crossed over non-Ed sheep they often produce Ed lambs but with white HST spotting markings, similar to those in the images below.
Unfortunately because these lambs are Ed, you have a 75% chance of their offspring also being this colour – which while spotted will not display any of the agouti colours that most people are looking for when breeding for colour. They’ll just be plain black and white (or brown and white since Ed displays as whatever the base colour is on the Brown locus). So if your aim is simply spots, dorper would be effective but if you want the agouti colours we wouldn’t recommend it.
The other question around use of Dorper and breeding goals would be about the wool. Dorpers being a shedding/hair breed, the fleeces on their lambs will be of low quality and would potentially shed. If that’s what you want, that’s great but it’s not a trait you’d normally find in Southdowns so if your aim is a pure Babydoll that breeds true to type, a wool breed may be a better option for bringing in the spots while retaining wool quality.
If wool quality is a consideration, we would suggest using a spotted ram from a breed that’s closer to the desired breed type – in this case Babydoll. The Down breeds tend not to have spots naturally occurring, however some of the other British breeds now have spotted lines. Romney or Corriedale may be a good choice as they have similar breed characteristics, or even a crossbred of the two. The important thing is that the closer the chosen breed is to your own breed in looks/characteristics, the easier it’ll be to stay with the type you want. For argument’s sake, we’ll use Romney in our example.
The aim would be to cross the spotted Romney ram over the purebred coloured (agouti) Babydoll ewes to get a line of Romney/Babydoll X lambs, each of which would be plain coloured but carrying the spotting allele. You would then have to do some selective close breeding (crossing these lambs with each other) to produce a spotted crossbred animal, then cross this back to purebred Babydoll ewes, to get 75% babydoll lambs that are carrying spots. You would then keep doing this until you get back to purebreds, but retain that spotting allele.
An animal is generally considered purebred if it’s more than 93.75% of the desired breed and breeds true to type, so that would be four rounds of crossing your spotted ram lambs back over purebred ewes to get back to purebred. This means that if each step takes two generations (one to get the spot-carriers, the next to get the spots), you’d be looking at 10 years to get your spotted purebred babydolls.
Note: Some registries do not accept spotted animals. Others require an animal to have a pure pedigree going back 5 generations to be eligible for registration. Therefore, if registration is an aim we would suggest checking with your breed registrar before undertaking a 10-year breed-up programme.
A note on close breeding – there is a lot of mythology around this, including the old adage “It’s line breeding when it works, it’s inbreeding when it doesn’t!” This is not actually true – there are specific definitions for line breeding and inbreeding (close breeding) which you can read about here, and both techniques can be useful to cement the traits you’re seeking.
There is nothing inherently wrong with inbreeding, however because you are crossing animals with similar genetic traits, those traits will be more evident in the offspring – which is why it’s so useful when seeking specific traits such as rare colours. However, it works for the unwanted traits as well as the desirable ones – any faults will become more evident and over generations the lack of genetic diversity tends to produce a weaker overall animal.
The way to counter this is to retain genetic diversity as much as possible. In the method we’re describing there are a couple of ways to keep the genetic diversity:
1. By starting with two unrelated spotted rams so that you could cross the offspring together without them being too closely related.
2. By buying in purebred ewes each time you use a close-bred spotted ram lamb from your breeding programme, so that new genetics are introduced in those offspring.
Regardless of which method you choose, it’s important to a) keep meticulous records of every breeding, and b) select and breed from only the very best of the lambs. If you don’t get a top quality lamb in a year, it’s better to wait another year for a good one than use an average animal for breeding.