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Posted: Tue Sep 02, 2008 2:07 pm
by strawberriesclint
Hi everyone
following on from my other discussion about the holsworthy sale on saturday. How would i actually go about having cattle tested to see if they are geneticaly short? Having had dexters for a while i didn't realise that just because the animal was short in height it dosen't mean they are SHORT. Confusing. Just goes to show you learn something new every day.
cyndy
Posted: Tue Sep 02, 2008 3:00 pm
by Sylvia
Short is what you decide the Dexter is by looking at it. Testing is to prove whether it is a carrier of the bulldog gene. If it looks short it probably is a carrier but it may not be. If it looks non short apparently it cannot be a carrier.
Posted: Tue Sep 02, 2008 4:11 pm
by Rutherford
Today you can take a hair sample and submit it through the Society to a genetics firm, the DNA will tell you whether the animal carries the bulldog gene, which reduces the skeleton size. The term ‘short leg’ is actually a misnomer; it is the whole skeleton that is reduced because the animal has only one working gene to supply the blue print for the growth of the skeleton. These animals do not breed true and will have calves of various types and sizes. The true breeding short leg is an animal with shorter limbs that will reproduce itself every time if put to a similar bull.
Beryl (Woodmagic)
Posted: Wed Sep 03, 2008 9:06 am
by Sylvia
Short carriers are generally bred to non-short to avoid bulldog calves. The resulting calf either resembles its mother and is short or its father and is non short. This does not seem to me to be 'not breeding true' the poor little blighters are doing their best with what their owners are offering them.
Elsewhere on this site is the firm statement that the skeletons do not differ.
Non short bred to non short get calves which are similar to their parents.
I do not know what the 3 out of 4 calves born to a short to short mating which are viable turn out like (the 4th being an unviable bulldog calf), I never risked it. I have asked this question before and not got an answer.
Are surviving calves from a short to short mating carriers or not?
The surest way to get animals which are identical to each other is to inbreed and it would, in my opinion, be a brave person who followed this path with Dexters.
Posted: Wed Sep 03, 2008 10:38 am
by Louisa Gidney
Simple Mendelian genetics for a short x short mating will give one homozygous non short, two heterozygous shorts and one homozygous short: the bulldog calf.
Posted: Wed Sep 03, 2008 10:43 am
by Rutherford
I was unaware that this question had not been answered on the board. I bred short to short for the first eighteen years of Dexters, in those days everybody did. I was the first to use a long leg bull openly. It is for this reason I can say the short don’t breed true. Short to short will give all shapes and sizes from very small to very big long leg, unlike the medium true breeder that will reproduce a similar conformation every time. My herd in those days ran from 36” to 46” withers height, when I began to use a non- carrier short bull and sold my remaining short cows the heights gradually reduced and today the whole herd is around the 40”.
Beryl (Woodmagic)
Posted: Fri Sep 05, 2008 12:28 pm
by Louisa Gidney
I mentioned the co-efficient of variation on another post and Rutherford's post above is a classic example of this in practice. Put simply, if you reduce the mean height (or whatever parameter you are measuring) you will at the same time increase the range to include both very small and very large. The coefficient of variation is the statistical tool to measure this and quantify it.
Posted: Fri Sep 05, 2008 1:21 pm
by Rutherford
For folks like me whose knowledge of maths is practically nil, I have no intention of descending into a discussion of the CV value of various genes. The message I am trying to get across is simply that without aiming for size, breeding from non-carriers only will leave a regular size, putting them on a par with other breeds, and in the case of a Dexter this will ultimately be an animal around 40|” to the withers
Beryl (Woodmagic)
Posted: Fri Sep 05, 2008 2:22 pm
by wagra dexters
Though we have never had any carrier stock in our herd, we did aquire a non-carrier heifer by Woodmagic Hedgehog 3rd out of an American imported carrier cow.
The reason that I pursued the purchase of offspring from the breeding lines of the American cow is because she has no history of introgression in her pedigree, which is quite rare. She also has extremely good legs & feet, and is generally a very nice cow, but in her case that was a fortunate co-incidence.
The tested carrier cow is 102cm, and the tested non-carrier daughter is now, as a mature 5yo, also 102cm, no taller than her carrier mother, obviously taking after her smaller sire.
Margaret.
Posted: Wed Sep 10, 2008 1:45 am
by Inger
The average height of a herd can be altered over the generations by consistantly using non-carrier bulls that fit within the breed standard for height. The thing is, you have to locate those bulls and hope you can keep the gene pool as wide as possible. A.I certainly makes that easier. As long as the height of the bull is noted in the stats on that bull.