Heterosis or the healthy mutt

Most livestock breeders have heard the term "hybrid vigour" in which the cross between two breeds grows better than either of the two purebred lines.  Heterosis is the formal name for this.

In the sheep world, commercial producers take advantage of this by crossing two maternal type breeds such as a Rideau Arcott with a Dorset to create an F1 cross.  The F1 cross is then mated to a terminal sire breed such as a Suffolk or Hampshire.  If done well, the resulting market lamb is superior than from each of the purebred lines.

We cross our two maternal lines so our F1 cross is a North Country Cheviot/Tunis cross. This hybrid is indeed strong, vigorous and grows well.  We are still working on which terminal sire breed works best with this cross and our production system.  We are trying a Hampshire cross this year.


With heterosis comes a certain degree of unpredictability.  However that unpredictability is reduced if the two parental purebred lines used are inbred.  While you always create your cross from the best of your purebred lines, the mixing of genotypes leads to less predictability in the resulting phenotype ie how the animal will look and perform. In some extreme cases the parental genes are incompatable and the hybrid is less vigorous than the parental lines. This is where data collection is very important.


It is common practice for breeders of purebred stock to line breed, that is mate closely related relatives to enhance desirable characteristics such a growth rate or conformation type.  This increases homogeniety and predictability of the offspring but also can come at a cost known as inbreeding depression.  The extreme of this is the appearance of lethal recessives such as spider syndrome in Suffolk sheep.


The reality is that breeding selection is focussed on relatively few measurable characteristics and the rest of the genome comes along for the ride.  In some cases the changes are positive, some negative but on the whole the inbred animal is less gentically fit than an animal that is outcrossed. 

While our purebred lines (especially our Cheviots) have some very desirable measurable characteristics, in my opinion, they are too inbred and we will be searching for unrelated lines to use for an outcross.


Lately I have been reading articles on the impact of inbreeding on disease and parasite resistance in sheep and am seeing the fitness advantage of the heterozygote.


There is very little in the livestock literature on the impact of inbreeding on parasite resistance but there is information on wild populations of sheep.  In these publications, inbred lines are more susceptible to internal parasites working as a natural selection against inbred lines.

Scrapie is another instance.  At first blush it makes sense to include selection for resistant lines in your breeding program.  However it never makes sense to breed for a single characteristic.  In this case, adding resistance to your flock should be done slowly without sacrificing production characteristics.  I know that in 18th century Britain scrapie was thought to be the result of inbreeding; maybe they were right. Is heterozygosity the way to go with respect to scrapie ie gaining some resistance, not sacrificing other characteristics? At this point I can honestly say I am not sure. We will continue to genotype and use quality rams with resistance genotypes.  However, we will not sacrifice quality in a effort to maximize resistance.

Breeding livestock is not a set formula but rather a dance where you go back and forth but ultimately make your way across the dance floor.  Your goal is to move forward but that requires knowledge, research and accurate,detailed data collection. I strongly feel that a wholistic approach needs to be used where the health, longevity, fertility and welfare of the animal has to be considered.  You may not make as rapid advances in characteristics such as rate of gain but I am banking on this approach reducing your costs by producing a healthier and more "genetically fit"  animal.


TTFN,


Laurie

If you are not eating Hawk Hill lamb, you are just eating sheep.

We have had two meals based on our purebred Tunis lamb and personally we thought the meat was delectable. A delicate aroma and flavour with fine-grained tender meat. Exactly what we had been led to believe by Tunis boosters.

We decided to put the lamb to a taste test and compared four different breeds of sheep. We tested our pure Tunis, our cross-bred Tunis/Cheviot, another Ontario lamb of a different breed from an organic farm and commercially available lamb from New Zealand. All were loin chops and all were cooked the same with no flavour additions. The lambs originating from our farm were both raised under the same regime though the Tunis Cheviot cross was about one month younger than the pure Tunis. There were four of us testing flavour, texture, aroma and taste. While not a true blind taste test it was the best we could do in a social dinner setting.

Well there was a significant difference in all the lamb. The least difference was between the Tunis and the Tunis/Cheviot cross. All of us preferred the Tunis and or the Tunis Cheviot. The Ontario lamb from another farm was not liked by any of us and the New Zealand lamb was in between. The Tunis and the Tunis/Cheviot had a more pleasant aroma, texture and flavour. The meat was more tender and the flavour was rich without a "wooly" after taste.

At one point I was considering selling our Tunis ewes and just using the Tunis/Cheviot crossbreds. Welllll.... the taste test has made me reconsider and the Tunis ewes are going to remain as part of our lamb production flock.

We then had the balance of the New Zealand lamb for our meal the next night. I am totally spoiled. Tunis rocks.

We are trying to encourage a meat marketing agency here in Ontario to run a chef-judged taste challenge. Growth statistics, conformation, carcass structure etc are all important but in your breeding program you cannot forget the most important factor - taste.

Later
Laurie

July at Hawk Hill

Well there has been quite a bit happening at Hawk Hill since my last post. All our lambs were born. We had 14 live births who now are nearing two months of age and are growing like weeds. Three of the purebred lambs are available for breeding stock and we are keeping 4 of the crossbred ewes for our own commercial flock. The balance are to be sold as market lamb. We absolutely love the Tunis/Cheviot cross lamb. They are hardy, fast growing and beautiful. There looks like a lot of nice legs in this picture.
Our cattle plans have changed radically since my last post. We took delivery of the two cows early in May and the first of the cows calved out in the middle of June. After she calved, she became extraordinarily aggressive and put me in the hospital. I have been out of commission for the balance of June and July healing.The cows are gone and we will just raise up our steers. After they get shipped next summer, we will change our focus to poultry and raise some guinea fowl.

We also made a really difficult decision and sold privately and by auction 10 of our horses in June. We now have 4 horses (Three Canadians and one Arab Canadian cross) for our own use. Lucan and Lilac are heading out for refresher training this fall. We are going to focus on getting ourselves and our horses out riding and driving.

Now we are hoping for the weather to improve so we can finish the hay.

TTFN,
Laurie