Cattle Size - Breeding Effects

[justmalc]

Please can someone clarify something for me. If a non short bull is mated with a non short cow will the offspring always be non short?

Further down the line, will the offspring of this mating carry a decreased chance of producing short offspring themselves even if mated with a short partner?

If the subsequent chances of producing short calves diminish, should breeders be required to notify purchasers of the decreasing likelihood of short calves as purchasers may, quite justifiably, be hoping for short calves from their non short purchase. In fact should cattle produced from a non short/non short mating be ineligible for registration due to the absence of the short trait from their genetic make up?

Grateful for an explanation/opinions.

Malcolm.

[Broomcroft]

Hi Malcom

These are the expected ratios you would get when breeding the following combinations:

Affected X Normal = 50% Affected, 50% Normal calves
Normal X Normal = 100% Normal calves
Affected X Affected = 50% Affected calves, 25% Normal calves, 25% Severely Affected calves
Severely Affected X Severely Affected (if it were possible) = 100% Severely Affected

Courtesy of the PDCA website.

You can obviously just have shorter/smaller animals that are Normal.



Edited By Broomcroft on 1209815492

[Rutherford]

For a number of years I bred in the general accepted way of the time. I used a short leg carrier bull and put it across the entire herd, so I can answer your questions from experience rather than theory. You can only breed carrier or ‘short leg’ calves if one parent is a carrier.
If a parent is a carrier, the two genes governing the skeletal growth are not a pair, one of the genes is not working, and if thrown to the calf cannot function. If the calf collects a second identical gene from the other parent, the calf will have no skeleton. i.e. it will be a bulldog. If however, the second parent throws its working gene the calf will have a partly developed or stunted skeleton, that is, it will be a short leg like its parent. Providing one parent is a long leg with two working genes the calf has to collect one sound gene and will not be a bulldog. If both parents are long the calf cannot collect a non-functioning gene and has to be non-short. If both parents are short there is obviously a chance that both will throw their dud gene leaving the calf with no skeletal growth.
Subsequent calves cannot be affected by a previous mating; their genetic make-up has to be solely the result of the genes provided by the two parents concerned in the actual mating.
Beryl (Woodmagic)

[Kathleen]

Hi Malcolm,

Just found this thread - hope the following clarifies a couple of points:

The gene responsible for Dexter Chondrodysplasia/Dwarfism (aka shortlegs) is a dominant gene (actually an imcompletely dominant gene - but as far as your question goes you need not worry about that too much) therefore it can not 'hide' for generations and pop out at some later date.

Consequently, as has already been stated, if you mate non-short/carrier X non-short/carrier then from that mating no resultant progeny will ever produce an animal that has the gene responsible for Dexter Dwarfism (in otherwords - you will NEVER produce a shortleg Dexter from two non-short Dexters).

A "Severely Affected" calf is a "bulldog calf" - ergo it is dead. It is an animal that is homozygous for the chondrodysplasia/shortleg gene.

And a 'bulldog' calf actually does have a skeleton.

Regards
Kathleen.



Edited By Kathleen on 1212946833

[sedgefen]

Re Cattle size
How can you have a non short from two shorts, bur not a short from two non shorts, which we did last year?
Lottie,
Sedgefen Dexters.

[Duncan MacIntyre]

This is not an effort at serious genetic explanation in technical terms, but may help.

A Non-bulldog carrier, commonly referred to as a long-leg Dexter, has two genes for leg lenght, both normal. It can only pass on normal leg length genes.

A bulldog-carrier, commonly called a short-leg Dexter, has one normal leg length gene, and one replaced by the bulldog gene. It can pass on either a normal leg or a short leg gene to its offspring.

So if we breed long to long, the calves will all inherit two normal genes.

If we breed long to short, we will get half of the offspring with two normal genes, half with one long and one bulldog, ie short-legs.

If we breed short to short, a quarter will get two long leg genes, one from each parent - long legs

two quarters, or half will get one of each, ie short legged

and a quarter will get two bulldog genes, ie will be a bulldog.

So two shorts will always produce a mix of long, short and bulldogs, but two longs can never produce a carrier animal since neither parent has that gene to pass on.

Duncan

[Rutherford]

Justmalc to go back to your original entry. The ‘short’ is a straight cross between a bulldog and a non-short. It couldn’t exist if it didn’t have the non-short gene. In the days when the short bull was always used, the breed was gradually dying out because of the prevalence of bulldog calves.
It should be borne in mind that most breeds have suffered to something similar to our form of achondrodysplasia. Only the Dexter has clung on and has not eliminated it, with many breeders insisting that the best exhibits were the carriers.
In the early part of the last century most beef breeders were cultivating different forms of dwarfism, thinking they were increasing the beef, but when the associated problems became apparent, the breed Societies set about eliminating the lethal genes.
Beryl (Woodmagic)

[Peter thornton]

"the breed Societies set about eliminating the lethal genes."

As should the DCS!

[Martin]

So, where to from here?
Short to short breeding, a definate no no as too many non viable calves.
Non short to short, too many variables ie. 25% of this 50% of that and 25% of the other.
Non short to non short, perfect! not quite peas in a pod, but animals of predictable height and type.

Ban breeding from carriers? Refuse to register animals that are carriers? Mark down all carriers at shows to encourage different breeding practices? What is the answer? Any of the above could spell disaster for the Society. What is needed is a clear and unemotional debate about the whole issue of the lethal gene. It is an issue that will not go away but I doubt very much that it is an issue that will be resolved easily or in most of our lifetimes.

[Rutherford]

Patience, we have already moved on. When I started we could never had this discussion. Nobody dared use anything except a short leg bull. Folks were horrified when I suggested at the AGM we should make a long leg available on A.I. The percentage of non-short is gradually growing. The membership will decide in due course. Meanwhile dictation would be disastrous.
I think we might justifiably insist that half the judges should come from those who only bred non-short. It does depend on the day on the judge’s own preferences. I know of some short breeders who would bend over backwards to be fair, but it is logical to assume that your own preferences must have some influence. I haven’t done a count but I think the panel is heavily biased at the moment.
Beryl (Woodmagic)

[Broomcroft]

I am not a fan of the gene and we are breeding it out. At the moment anything that look like carriers go into the food chain. I am only keeping any bulls entire that are non-carriers but are also a bit shorter than the rest. The two bulls I have retained are both shorter than any non-carrier steer I have on the farm, but they're still not short. Just hope they pass it on! That's why I wanted the height prediction chart based upon Wagra's data. I also want them all to be red just to make life even more difficult.

I would like to see the dwarf gene go, over time, but not too long either. All other societies have eliminated it, and those societies still exist and I think are flourishing (Hereford for example). I would welcome a sensible debate on the issue because apart from anything else I would like to know more. What are the issues? What is the benefit of the gene? Is it an animal welfare matter? How often does early arthritis set in?

The other thing that may be changing is that some fairly sizable beef herds are setting up which is hardly surprising as it's the best beef available. I'm one and I know of others. To me, carriers are not commercially viable for beef. Too variable apart from other issues.



Edited By Broomcroft on 1213028608

[Peter thornton]

Totally off the cuff, here's how it could be done.

1. Announce that as from 2015 all show winners will need to be tested as non carriers

2. Choose judges who favour non carriers and subtly tweak the judging standards to favour short "non shorts" if you se what I mean.

3. Er, that's probably enough.

[Duncan MacIntyre]

Although I aim at producing non carrier cattle of traditional short dexter size, and to that end have no carrier animals in my herd, and actively encourage others to do likewise, I do think we are nowhere near a stage of saying "off with their heads" to all the short legged cattle out there. This is one of the areas in the breed where we need a bit of tolerance and understanding of other point of view than our own. It may be that in the future with the help of DNA testing we will be able to produce a substantial number of "short" non carriers, all we should be doing at the moment is allowing the numbers of these to build up slowly and to improve in quality. At the momemt if we pushed for extermination of carrier animals we would kill the breed stone dead.

Duncan

[Colin]

I don't know whether this will be of interest, but I've created 3 simple spreadsheets to predict the percentage chance of a type of calf born to different types of mother and father. One spreadsheet for each of:

1. short(carrier)/non-short(noncarrier)
2. true red/wild red/black
3. horned/polled.

Also by looking at the type of calf actually born, you may be able to work back to determine whether a parent is heterozygous or homozygous for a particular attribute.

Can't put these on the bulletin board, but if they are of interest, perhaps Clive you could put them on the web page with your weight table ?

Colin

[Broomcroft]

Sounds good Colin. If you send to me by email and I'll have a look. clive@broomcroft.com



Edited By Broomcroft on 1213126271