Author Topic: Portland sheep article in The Ark (Read 22055 times)

Anke · « **Reply #45 on:** November 01, 2011, 12:24:56 pm »

The cattle were enclosed in the early 1300s as means of shooting/hunting/food source, but never tamed or handled by humans. That made them safe from the (Scottish) Border Reivers in what were fairly lawless times - they could not be herded and driven away. They are fenced in by stone walls and the flock has never been added to nor have any animals been taken away for breeding somewhere else. These are wild cattle!

That also means that the genetic base is developed from what it started out before any real improvements in animal breeding were made by man, and the fact that there was (and still is) no selection of breeding stock, the strongest bull is in charge for a period of about 3 years and mates all the females. Female calves do not breed until they are about 3 years of age, so father/daughter matings are very rare. Genetically all animals are identical, and bear no resemblance to any other catte breed in the world. They are not massive, have strong shoulders, smaller rear ends (so they can run fast!), calves are born very small (and no difficulties in calving, which happens all year round) and lead bull decides if the calf is accepted by the herd. If he thinks it's not, it is either abandoned by the mother or killed by the bull - weaklings do not survive.

Have a look at their website!

But with regard to other rare breeds - we often keep all animals that can survive with human help, breed from them etc etc. It is often said that prolonged in-breeding a group of animals wll produce a smaller, weaker animal that needs outside blood to re-invogorate it. However these cattle have never been added to, so what's all that about? Human intervention etc etc.

It is just interesting, but it's an experiment that cannot be carried out by anyone on any other rare breed.... after all who can plan nowadays for 800 years ahead...

kanisha · « **Reply #46 on:** November 01, 2011, 12:34:41 pm »

Quote from: Anke on November 01, 2011, 12:24:56 pm

That also means that the genetic base is developed from what it started out before any real improvements in animal breeding were made by man, and the fact that there was (and still is) no selection of breeding stock, the strongest bull is in charge for a period of about 3 years and mates all the females. Female calves do not breed until they are about 3 years of age, so father/daughter matings are very rare. Genetically all animals are identical, and bear no resemblance to any other catte breed in the world. They are not massive, have strong shoulders, smaller rear ends (so they can run fast!), calves are born very small (and no difficulties in calving, which happens all year round) and lead bull decides if the calf is accepted by the herd. If he thinks it's not, it is either abandoned by the mother or killed by the bull - weaklings do not survive.

But with regard to other rare breeds - we often keep all animals that can survive with human help, breed from them etc etc. It is often said that prolonged in-breeding a group of animals wll produce a smaller, weaker animal that needs outside blood to re-invogorate it. However these cattle have never been added to, so what's all that about? Human intervention etc etc.

[quote/]

Yes I thought that was your point. the point as I understand it is that genetically similar populations are viable if the selection process is designed not for phenotype but survivability. that they have similar phenotype is due to relatedness not selection for phenotype. the danger with these populations as has been found with other genetically inbreed populations is they are at huge risk of disease as there is so little genetic variance to provide some resistance if one gets it they all do. ....................... putting all your eggs into one basket comes to mind.

PatsyPortland · « **Reply #47 on:** November 02, 2011, 12:07:12 am »

The Portland is a small and thrifty breed, adapted to graze the commons and exposed clifftops of the Isle of Portland, and renowned for the fine texture and flavour of its meat. The fleece is highly regarded by handspinners and is classed as Fine by the Wool Board. Most flock owners cite the small and easy to handle qualities of the Portland as a major factor in their choice of breed. Sheep of large size have often been associated at card-grading with the occurrence of coarse and atypical wool. If slow maturation and thrift are related, then the large size and early finishing times of the large types may indicate a further departure from Portland Breed type. Conservation of Rare Breeds should preserve such individual characteristics for the future, rather than “improve” through introgression, whilst retaining variation in the gene pool.

Evidence of introgression from DNA profiling has been associated with animals of very large size. Since larger size is inevitably rewarded both in the Show ring, and at Sales, this introgression has had and can be expected to have a profound influence on the Breed if allowed to proliferate unchecked. Inexperienced Breeders less familiar with the breed description and subtleties of type could be expected to be most at risk of influencing or founding their flock with atypical animals.

The Portland Sheep Breeders Group (NOT a Society – the RBST’s Combined Flock Book is the registration authority for Portlands) has advised and agreed with RBST an amendment to the Breed Description giving information on size in rams, which will be published in the Combined Flock Book. Judges and card-graders will also be notified.

Further information will be available shortly through the Newsletter and Website of The Portland Sheep Breeders Group
http://www.portlandsheep.org.uk
The Group is planning card-grading workshops for its members, why not join? New members are very welcome

kanisha · « **Reply #48 on:** November 02, 2011, 06:48:51 am »

Hi can you explain more about introgression and DNA sampling, has this been done in the Portland? If so I would like to send you a pm for more details. I have looked at the Pedrose et al study . Mitochondrial diversity and the origin of Iberian sheep and alvarez et al - Genetic relationships and admixture among sheep breeds from Northern Spain assessed using microsatellites Do you have a copy of the study for the portland?

many thanks

TheCaptain · « **Reply #49 on:** November 02, 2011, 08:17:20 am »

What's your definition of introgression? As far as I can see it is basically the adding of other types of genes to a species; which isn't what we have been talking about.

So what your saying is that those animals that have been of larger size are not pure bred? If that isn't what your saying, and these animals can be proven to be pure, then isn't the breed evolving?

My land is completely different to that found on the exposed clifftops of Portland; far lusher and a far nicer lifestyle. As previously discussed, this may influence the size of lambs that are born and subsequently raised. If you introduce a 'size limit' then I may not be able to continue registering my sheep. If I don't have pedigree Portlands then what's the point? I got Portlands as they are my local rare breed and I believed that I was doing something to make it less rare. Right or wrong, I still think that it is extremely short sighted to introduce such standards before making the breed a bit less rare.

Regarding membership; I was a member in my first year of keeping them and had been meaning to get round to renewing it but I was massively disappointed to see that the group had decided to essentially boycott the Gillingham and Shaftesbury show (due to poor organisation the previous year) - well done on promoting the breed. I also don't like being given the third degree by one of the other members, who rang after seeing an advert in our local mag, over what I'm selling and who I am selling to.

kanisha · « **Reply #50 on:** November 02, 2011, 11:45:18 am »

Captain, I may be able to help a little here as I have a breed where there is a very specific height requirement we all measure our sheep alot!!

It is acknowledged that height is a polygenic trait so two parents can produce offspring with varying height potential in that sense height is genetic however it is also environmental and with the ouessant that potential for height is reached in optimum conditions ( good grazing) but the height restriction still remains. this means I could breed a lamb that eventually goes over height. I don't know how the system works in portlands but currently I can use that sheep for breeding but it won't get confirmed as of breed but its offspring maybe if they met the height requirement however careful selection for its mating would be needed to get the height down. In my case I try to select small rams to balance out any greater potential for size in my ewes leaving me with roomier ewes for lambing and hopefully nice small lambs. I don't know if that helps a little.

SallyintNorth · « **Reply #51 on:** November 02, 2011, 03:15:45 pm »

Well, kanisha, that's fascinating - thanks for writing it up.

So, it seems to me that, if a lot of rare breed animals get kept on better ground, we could potentially end up with genetically smaller animals! As each breeder selects smaller rams to take the size off their well-grown ewes, the underlying genetics could, if taken back to the harsh native environment, result in even smaller sheep than the original population!

Food for thought indeed! And definitely should make the breed standard authors think long and hard before introducing a height restriction.

I now feel more informed about why over-height Dales ponies can so often be amongst the rosettes, despite it being instant disqualification to be found to be over 14.2hh.

kanisha · « **Reply #52 on:** November 02, 2011, 03:51:48 pm »

Hi Sally there is plenty more to determining height in a ouessant there is a minimum as well as a maximum and also an ideal weight. there is also something known as a forchette which gives a range of heights which would be expected for the yearlings rams and ewes and when adult final height is given in the sheeps second year as long as it isn't borderline in which case it may be withheld for a year to check they don't go over. however no sheep judged over height gets past the pre comeptition exam and is left shamefaced in the pen

beware the unsuspecting novice who takes their too tall sheep to the show!
On the other hand when your breed has the title of the worlds smallest breed of sheep ( non miniaturised) you can't afford to let the height drift. even the person accredited with saving the ouessant acknowledged that environment had its part to play and the sheep did best on their native granite rock grazing.

From my own perspective having looked at the history of the breed the grazing conditions on the island were untenable it is recorded the sheep died in their hundreds every winter ( 6000 sheep on a 1500 hectare island where only 20 %max was allocated for grazing and included 2000 cattle and native miniature ponies that the ouessant is small is due to its exceptional historical living conditions which I doubt anyone would repeat today it is a sad fact that any move away from the breeds original place for formulating the breed will change the breed. the standard does seek to preserve that which was and not that which is.

TheCaptain · « **Reply #53 on:** November 02, 2011, 06:33:59 pm »

Quote from: kanisha on November 02, 2011, 03:51:48 pm

it is a sad fact that any move away from the breeds original place for formulating the breed will change the breed. the standard does seek to preserve that which was and not that which is.

I don't see why that is a sad fact?!?!

Essentially, if I keep my sheep for the rest of my life, breeding from the same lines of ewes over generations, that they will lose the very thing that makes them Portlands - the hardiness, thriftiness etc. regardless of size, as my land is a world away from what you find on Portland? They'll still be pedigree Portlands though.

Seems we're swimming against the tide of environmental evolutionism...

kanisha · « **Reply #54 on:** November 02, 2011, 07:41:38 pm »

Not if there is height restriction and you don't select for it

VSS · « **Reply #55 on:** November 02, 2011, 08:28:11 pm »

It's called selective breeding. Most of the breeds we have in the UK today are (in their current form) not much more that 150 years old (with the obvious exceptions of the primitives and some other older breeds). New breeds were developed to do a particular job often in a particular location by crossing and then selecting offspring for the desired characteristics.

It is only with the development of breed standards that this "evolution" has stopped or slowed. Is it a good thing? Not my place to say, but an interesting thought.