A Few Facts on the Principles of Breeding
Uploaded May 2005

As a result of a query on the website notice board, I will attempt to explain some of the basic "mechanics" of pig breeding. To tackle the subject of genetics in depth would require a pretty hefty tome, so I will limit this article to cover a few basic facts. We owe a great deal of our understanding of the principles of breeding to a 19th Century monk by the name of Mendel. Despite the great advances in work with genetics, much of Mendels' work still holds good today.

Although Mendel experimented with plants, the same principles apply to livestock breeding. The sire & dam have an equal influence on the progeny of any mating, but those progeny will inherit different characteristics in a random way from each parent, hence the variation in type in piglets from the same litter. The aim of any livestock breeder is to attempt to mate a pair of animals which will produce progeny with the qualities he is looking for, but without undesirable faults. Breeders find that a champion sow & boar mating does not guarantee prize winning progeny, but a cross between certain lines will produce the desired result. This is what makes livestock breeding interesting, were it not the case the person with the champion sow & boar would never be beaten!.

However, if one consistently breeds from good stock over a number of generations, rejecting inferior progeny, the increase in the genes carrying desirable traits, will improve herd quality. Should they breed a very good animal, experienced breeders may use line breeding or in breeding as a means of concentrating the genetic make up of that superior animal, (line breeding: crossing of fairly closely related animals, in breeding: mating closely related animals, eg brother & sister). The drawback to close breeding is that undesirable traits, which may not be apparent in the parents, will also be exaggerated in the progeny who may also suffer from morbity or metabolic defects. Close breeding should only be practised by experienced breeders who know the risks involved. Should the result of line or in breeding produce a top class animal, his genetic purity will enable him to stamp his mark on all his progeny.

Within a minority breed, because of the limited genetic base, it can be quite difficult to obtain unrelated stock. The mating of animals with no genetic relationship can produce a hardier animal with better growth potential than a pure bred, this is known as "hybrid vigour", but mating two hybrids would result in a very mixed up assortment of piglets, hence the importance of using pure bred boars on crossbred stock.

The BPA system for the registration of pedigree pigs, requires all males to take the sires' name & all gilts the name of the dam. This has not always been the case, for many years breeders could name their pigs as they wished. This current system makes it easier to trace pedigrees & is helpful when planning a breeding programme. Although one would expect boars eg from the Peter Lad line to have a very similar genetic make up, this may not be necessarily so. If a Peter Lad boar is crossed with a sow who has no PL boar in her parentage, the resultant boars from the litter will be Peter Lads. But they will only be at most 50% PL If this boar is mated with another sow with no PL in her breeding, that resulting boar will be only 25% Peter Lad. And so it goes on. However despite this dilution & despite the continual evolution of breed, pigs both male & female will exhibit a consistency of type recognisable as a particular bloodline. For instance the Royal Lustre sow line produces "pretty pigs", the Freight Train boar line, despite being very much diluted, just one or two litters from the original semen importation, consistently turns out finished pigs with lower fat levels than other boar lines.

Breeding livestock is a fascinating business, the simplest & safest way to breed better stock is to take a lesson from nature, where only the strongest & fittest survive to ensure survival of the species, breed only from the best & let go the rest.

John Mason