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Author Topic: polled gene  (Read 4983 times)

humphreymctush

  • Joined Jul 2010
  • orkney
polled gene
« on: December 21, 2011, 09:11:01 am »
When I used to use a North Country Cheviot ram on my shetlands a lot of the ram lambs had horns so clearly the polled characteristc of the cheviot was not very strong. But since I have been using a suffolk ram I never seem to get lambs with horns.
So I am wondering about the strength of the gene that makes Suffolks polled. Heres why:

My suffolk ram is getting very old and toothless but instead of buying a replacement I want to breed a new ram and I am considering crossing him with a couple of very old hebredian ewes that are the last remnant of a group I bought many years ago and are definately the best of that bunch.
I would prefere it  (or rather the abatoirs would prefre it) if the lambs I produce by crossing this theoretical Hebredian/Suffolk ram lamb with my Shetland ewes were polled. What are the chances?

(I normally castrate and this seems to inhibit horn growth somewhat in the pure shetland wethers.)

SallyintNorth

  • Joined Feb 2011
  • Cornwall
  • Rarely short of an opinion but I mean well
    • Trelay Cohousing Community
Re: polled gene
« Reply #1 on: December 21, 2011, 09:41:52 am »
I don't know the inheritance mechanisms for polled in sheep - but someone who does will probably be along soon!

Blue-faced Leicester on horned Blackface and Swaledale ewes produce predominantly polled Mules.  So from that it would seem that polled can certainly be dominant.

And yes, with horned Swales and unpolled offspring from crosses, horn growth is never as pronounced in castrated wethers - in fact from about 5 months old you can pretty reliably pick out the uncastrated members of the group from the size and weight of the horns.
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kanisha

  • Joined Dec 2007
    • Spered Breizh Ouessants
    • Facebook
Re: polled gene
« Reply #2 on: December 21, 2011, 06:34:36 pm »
The chances of producing lambs with some horn growth from a hebredian cross ram are in the region of fifty percent upwards  in the lambs

Horned in rams is basically incompletely dominant to polled. so in a cross breed ram presumably carrying both the polled gene and a horned gene.and with a phenotype that is likely to be horned or scurred the likelihood of a ram lamb with horns is in the region of fifty percent either fully horned ( homozygous) with the rest horned/ polled heterozygotes assuming all your shetlands are homozygous for horns. The heterozygote lambs  would likely produce scurs of varying rates of horn growth..

If you have found that the suffolk produces significantly less horn growth in the heterozygotes then it might be hopeful to have less horn but that is going on your previous past experience.
« Last Edit: December 21, 2011, 06:37:16 pm by kanisha »
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humphreymctush

  • Joined Jul 2010
  • orkney
Re: polled gene
« Reply #3 on: December 21, 2011, 07:55:13 pm »
What about the ewe lambs Kanisha? If all the ewe lambs are polled and 50% of the ram lambs then 75% in total wont be too bad.

kanisha

  • Joined Dec 2007
    • Spered Breizh Ouessants
    • Facebook
Re: polled gene
« Reply #4 on: December 21, 2011, 08:36:06 pm »
ewe lambs is more tricky there is a sex linked horned gene (horns only in the rams and a horned gene rams and ewes. Hebredians have horns both sexes but shetlands generally the ewes are polled......... anyones guess what will come to the surface but I would suspect more scurs   ( incompletely dominant heterozygotes of some mix or other) than full horns.
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Anke

  • Joined Dec 2009
  • St Boswells, Scottish Borders
Re: polled gene
« Reply #5 on: December 21, 2011, 10:00:31 pm »
My suffolk ram is getting very old and toothless but instead of buying a replacement I want to breed a new ram and I am considering crossing him with a couple of very old hebredian ewes that are the last remnant of a group I bought many years ago and are definately the best of that bunch.
I would prefere it  (or rather the abatoirs would prefre it) if the lambs I produce by crossing this theoretical Hebredian/Suffolk ram lamb with my Shetland ewes were polled. What are the chances?

(I normally castrate and this seems to inhibit horn growth somewhat in the pure shetland wethers.)

Wouldn't you loose quite a bit of size in any future offspring, as a Sfflk x Heb tup would already be smaller than a pure Sfflk? Couldn't you get a new older sfflk tup or tup lamb and so guarantee both size and no horn for any lambs?

Also in pure-bred shetlands I have found that some wether lambs have nice wee (actually tiny, but not scurrs) horns and some have none, all offspring of the same tup, so there must be some influence on the female side too...


humphreymctush

  • Joined Jul 2010
  • orkney
Re: polled gene
« Reply #6 on: December 22, 2011, 10:59:30 am »
I actually want a smaller tougher ram so that the lambs are hardier and born more easily. Also I will be able to use him on shetland gimmers. For me size is not the issue. Appearance is important because the people who buy store lambs here are very conservative. As long as the lamb look like a Suffolk or a Texel you get a good price per kg. I would prefere to breed all my shetlands pure but if your lambs look at all weird or wonderful you get peanuts. All my Shetland Suffolk lambs look like Suffolks, just a bit smaller. None of the colours or markings or horns seem to be passed on so I get a good price. The Shetland Cheviot cross lambs I used to breed comanded an excellent price as breeding females but the wethers were not sort after.

Anke

  • Joined Dec 2009
  • St Boswells, Scottish Borders
Re: polled gene
« Reply #7 on: December 22, 2011, 04:30:39 pm »
Ok, I was just wondering....

I have so far been using Shetland txl cross ewes on a shetland tup and have found that the lambs sell well as "light lambs", just before Xmas (between 30 and 35kgs). Sold some last week and got 2 pounds/kg, so was feeling quite chuffed with them. Using a txl this year though...

I have found that horns/scurrs don't matter on lambs sold for slaughter.

humphreymctush

  • Joined Jul 2010
  • orkney
Re: polled gene
« Reply #8 on: December 23, 2011, 12:06:32 pm »
Thanks for that. I think I will just give it a try.
The other think I might do is but an old Suffolk ewe and hope I get another Suffolk ram next year.
Part of my dilema is that my old ram is quite exceptional in terms of his length and the relative fineness of his head (for a Suffolk). The ones I have seen recently are also much heavier around the shoulders which I think all contributes to lambing trouble.

SteveHants

  • Joined Aug 2011
Re: polled gene
« Reply #9 on: December 23, 2011, 10:38:16 pm »
I had thought the horn/polled gene was coded for on a couple of pairs of genes because you can get 4 phenotypes:

Horns
Scurs
Polled
Double-polled (little dips where the horns should be)

Lleyns, for example, are double-polled. This makes them ideal for crossing to horned breeds to produce poled offspring - the most you will is scurs if one of the parents is double-polled.

I had no idea it was possibly sex-linked too.

I have read no published papers on this - this is just what I gleaned (coupled with supposition) from a semi-scientific verbal explanation I once had. However, I was looking at sheep to buy at the time, so my ind was on that, really.

kanisha

  • Joined Dec 2007
    • Spered Breizh Ouessants
    • Facebook
Re: polled gene
« Reply #10 on: December 24, 2011, 10:29:46 am »
Hi Steve,

I think horn genetics is more complex than can be simply explained and is in all probabilty polygenic. I am unaware of double polled or how this might incorporate itself with the other genotypes. I have been following the basic horn genetics as used by shetland breeders in the US prefering to breed polled shetlands. I have found in Ouessants ( which are sex linked the ewes are hornless not polled) that it works well although Humphrey's point re his suffolk may well be an example of the double poll  genetics that you  have pointed out.
for a simplified version of the basic genotypes ( double polled excluded) this site works well.

http://www.saltmarshranch.com/genetics/polling.shtml

It is written by Prof Steven Weaver  former genetics research and teaching professor  at the University of Illinois in Chicago. so whilst no doubt simplified I would think pretty representative of genetics as found in primitives but I would agree that there is more to it than a single gene. I had considered a growth rate factor as an additional component which may equate to double polled. I am playing in my own way with both growth rate factors and cross sectional horn shape  in my sheep ( the variation in ouessant horns is a puzzle that gets me scratching my head!)

If you have more information on double polls I would be very interested
« Last Edit: December 24, 2011, 10:33:25 am by kanisha »
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