Breeding strategies - inbreeding, line breeding and outcrossing

By Marylyn Stevens
Everything in a living being is centred on reproduction. There are living beings on earth today because other beings have reproduced with desperate eagerness for two thousand million years or more.

In the simplest sense the term “breeding” means no more than just reproducing, as a result of a sexual union between two living things of a kind. This is what goes on in the wild, with the environment as the only controlling factor. In this way nature does only a limited amount of selecting because it is only concerned with reproducing and survival of the fittest.

For the stud sheep breeder there is a wider and more significant meaning.  In order to satisfy the demands made by an ever changing human society and clientele, their aim is not merely to give continuance to the species, breed or strain, but to manipulate with the material available in such a way that they may produce colour and shape in compliance with certain predetermined rules and public demands.  This means a high degree of selection and a knowledge of some of the definite facts which operate to influence the various characteristics which are peculiar to the new individual.  Thus the ordinary conception of breeding becomes an art and a science, and the more one realises this and is able to put it into practise, the more successful and satisfied one becomes.

Even though more sheep breeders than ever are prepared to apply the principles of heredity, there are still some who either fail to appreciate the significance or whom are so smugly satisfied with chance methods that they ignore or even reject the whole idea.  Perhaps the trouble is that when scientific matters are suggested, all too often a feeling of “can't be bothered” or “I wouldn't understand anyway” comes out.  This is a big pity, for quite frankly all that is really necessary for the average breeder is the more elementary part of the subject.

I have already said that the breeding stud stock is a form of art.  You the “artist” can either practice simple art or make it more complicated, but either way, there are a few rules to follow if you want to succeed.
There are a few main factors that control the sheep you breed – heredity and nutrition. This combination is most relevant in the wool – you can select and mate for wool and see a definite quick result, but if you do not feed properly with balanced nutrition, you observe deterioration in that fleece. 

Some inherited characters respond rapidly to selection whereas others are very slow or show no response at all in the first generation.  For example, one character in the sheep that I breed that I find easy to correct (or mess up ) is wool type and density, while one that is heritable weak is twinning.  Selection for breed improvement should only be made on a performance under commercial conditions.

Quick advances may be made in breeding using AI and embryo transfers, and in the not so distant future cloning will be possible, whereby you will be able to have a paddock full of look a likes if you wish (rather boring don't you think) also the possibility of adding genes e.g. genes to prevent some of our diseases and dividing embryos is not far away.  However for the present in the sheep industry except under very special circumstances is it unlikely to justify the trouble and expense involved.  Natural breeding is much easier, much less costly, just as fascinating and depending on the interpretation of the stud-master, much improvement can be gained.  There are very simply three methods of breeding available to the stud breeder or as is more usual a combination of the three.
 
Firstly 
INBREEDING
Inbreeding is a method of controlled breeding in which definite results may be obtained in well directed breeding in the shortest possible time.  It is a method by which most modern livestock breeds were established.  This does not make it the perfect system – there is no such thing.  Inbreeding could be just as dangerous as it might be beneficial.  Many breeders question it's use, but their attitude is usually due to a failure to fully appreciate what happens during inbreeding, and also to the failure to carry out any heavy culling caused by inbreeding.  Inbreeding is a mean of looking in on your attributes.  These “unseens” are brought out in inbreeding because they are caused by recessive genes.  When inbreeding, a recessive gene doubles and becomes dominant.  Consequently heavier culling is necessary to get rid of any previously marked weaknesses from a breeding stain, but the resultant stock are “purer” and more likely to breed true.

I always join a stud sire to several of his daughters to uncover any undesirables, sometimes with surprising results, sometimes very predictable.  Always join several daughters and get an average assessment of the progeny.  The next generation reveals even more.  In most cases continued inbreeding in sheep brings about reduction in size and vigour and susceptibility to disease.  If you contemplate an inbreeding programme, the individuals to be used as a foundation stock must be of impeccable heredity material, if they are not, the unsound qualities that are concealed will come to the surface and ruin the stain.  It is of course a vain hope that an animal which lacks desired characters will transmit them.  An inbreed stain cannot be any better than the animals from which it came. 

As I see it, inbreeding has a place in the breeding of stud sheep and that it is:

1. To find hidden faults.
2. To impress a particularly good feature on a stud in a short time.

 
LINEBREEDING
Line breeding in simple terms is a modified form of inbreeding.  It is the building of a pedigree in which one individual occurs repeatedly.  It is possible to line-breed several individuals at once.  This is the method of breeding that I find gives the most stable sheep, the most complete sheep – the sheep that if I could guarantee it, goes closest.

You have room to move and manipulate within a pedigree of line-breed animals.  There is only one proviso and that is, that the animals being line-bred into one pedigree are of the one line.  Imagine a set of coloured blocks (genes) stack them in a certain way and you get a picture.  Stack the same blocks in another way and you get a different picture – you can have a whole flock of different pictures, but you have only used the same blocks (genes).  It is not possible to line-breed without inbreeding to some extent, but it is possible to inbreed without line breeding.

Linebreeding is the best, safest way to breed top quality stock that have an inbuilt guarantee.  The storage of semen and embryo transplants are becoming an alternative way of saving bloodlines, but they do cost money.  If you examine the records of bloodlines of any pedigree stock, the fact is revealed that success has usually come from those animals which have been produced by linebreeding to some famous animal of their sort.
 
OUTCROSSING
 As is suggested, means the introduction of an animal into a line, from some other line or even from some other breeding.  A breeder can introduce one strain into another strain or on the other hand a breeder may continually by out crossing to different lines, in which case because all the breeding is unrelated, the whole thing becomes entirely without system whatsoever.  Pedigrees become very involved and almost useless and any results is mere chance.  Outcrossing does however have a place.  It may be found that in a particular line a   particular feature is not available. In this case a selected outcross would become necessary and when the desired feature is obtained, revert again to line breeding.

Outcrossing can introduce a needed quality, but please do it with caution as you must remember that an individual transmit its faults as well as its good points.  Many good breed of livestock have started with an outcross – to name a few of the successful ones, we have South Suffolk's, Corriedales, Poll Dorset's, Perendale and others.  However to maintain and stabilise these good breeds line breeding and to a certain extent inbreeding were still and still are being practised. 

Each method has its advantages and disadvantages, but if I had to make a decision and stick to it I would linebreed, with perhaps a very occasional outcross.

Just a few personal observations that I have made from the sheep I breed...

1. Before commencing line breeding, you must have an image in your mind of what you wish to create and then use only the animals that come closet to your vision.  Don't change your image midstream
2. The most influential individual in a pedigree is the maternal grand-dam, secondary is the paternal grand dam.
3. Unless you practise line breeding to retain a bloodline, consider it lost after five generations.

 
I would now like to just touch on the subject of crossbreeding with an outside breed. Crossbreeding today seems to me to be a more acceptable tool in the stud industry than it used to be.  There are observations of it having been used in the cattle industry and to a lesser extent the sheep industry.  Just a few years ago it was frowned upon and many still do, but I guess because of the demands put upon breeders to forever perform to a high standard, and to do this at a fast rate, both in the stud arena and the commercial filed, some have thought it worth a try.  It is my opinion that this form of crossbreeding in the stud industry should only be carried out for a very definite purpose by those well versed in the subject, and only when some character is wanted which does not occur within the original breed or which has shown a distinct downward trend within the original breed.

There must always be a quite definite purpose, and as soon as the required feature has been transferred the crossbreeding must end.  It is then the stud breeds job to go on selecting for and maintaining the newly acquired attribute.  Generally in crosses between breeds it is found that hybrids produced are larger in weight and skeletal measurement than their parents.  This is referred to as hybrid vigour. 

However, when crossbred animals are mated together the tendency for this added vigour disappears in the following generations.

When crossbreeding is being undertaken by the stud masters of a breed, the breed descriptions takes on a greater importance.
 
LOOKING BACK
If I could have my time over again, I would most certainly breed stud sheep.  I have found stud breeding a most rewarding challenge and very time consuming – which I like.  There always seems to be a future, a new hope, a new aim.  Unfortunately, it is not the way to get rich money-wise, but one does make many friends and the learning is never ending.  It is a job that is never done, simply because we try to do the impossible, and that is to breed what in everyone's eyes is the perfect animal.  There is no such animal, because we all have different eyes.
To begin stud breeding there are decisions to make.

• Consider your climate and locality.  Consider the popularity of the breed, its acceptability to others, its marketability.
• Do you like the breed?  This is so important, as you will never do well with a breed, no matter how well it sells or what others tell you about it, if you don't like it.  Remember it is you who has to live with it.

You've decided on the breed.  If you want stud sheep you must have registered stock from a registered breeder.  Choose to buy from a breeder of good repute, one that consistently produces good stock and I put emphasis on the word “consistently”.
Lots of people when starting a stud buy their ewes from one breeder and a ram from a totally different stud and line.  To this I can only say don't with a capital “D”.  Now you can see why I said go to a consistently good stud master.
Having got your stock get your “eye in” on them in your own paddock in your own time.  We'll assume that the please you, then stick to that line create your own animals and go from strength to strength.
If they do not please you then you can get an outcross ram if you wish, but be careful.  Then settle down and take a little longer to create your own animals.  Remember what I said about coloured blocks and you can stack them as you wish.  Keep your pedigrees and records.  It does help in the stud work to have a good memory and a photographic brain.  However this is not essential if you keep records, but devotion to duty and a determination to succeed are absolute necessities.
 
In concluding I would like to give you a problem to ponder. As a stud sheep breeder, you are the keeper of your breed, we must assume that you love the kind of sheep you have e.g. Suffolk's, Romney's, Cheviot's or whatever.  You have that breed at heart and want nothing better than your breed to flourish with “abandon” - ok.
Now just let’s say that the opposite is happening, that your beloved breed is on the decline, on the road to oblivion.  What are you going to do?

1. Continue on and hope that something or someone will come to the rescue.
2. Practise intensive inbreeding or intensive linebreeding and produce some magnificent individuals that sets the breed away.
3. Rush out and buy an outcross from your floundering breed.
4. Put another breed through that you think has the feature that is causing your breed to fail.
5. Go on as you are and maintain a pure breed for future generations to use.

Think about this.
 
I said in the beginning that a stud breeder is an artist with several tools at his disposal, no matter which way he uses them stud breeding comes back to the ability of the stud master to create a sheep just as an artist paints a picture.

I do wish you all great success with your sheep breeding.

Thank you
Marylyn Stevens

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