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Linebreeding / Inbreeding

Line breeding is the most conservative form of inbreeding. It is usually associated with slower improvement and limited risk of producing undesirable individuals. It can involve matings between closely or distantly related horses, but it does not emphasize continuous sire-daughter, dam-son, or brother-sister matings.

The main purpose of linebreeding is to transmit a large percentage of one outstanding ancestor’s genes, in this case Royal King, from generation to generation without causing an increase in the frequency of undesirable traits often associated with inbreeding. Because linebreeding is not based strictly on mating closely related individuals, it does not cause a rapid increase in homozygous gene pairs. Consequently, it will not expose undesirable recessive genes as extensively as closebreeding. For this reason, linebreeding is generally a safer inbreeding program for most breeders. It is well documented that linebreeding strengthens characteristics, as with linebred Poco Bueno horses which exhibit specific characteristics for more bulldog type and muscling. Certain characteristics are ”set” and inherited from generation to generation when linebreeding is continually practiced.

The purpose of inbreeding is to fix certain traits or the influence of certain ancestors’ (e.g. Royal King) upon the progeny. This procedure varies from intense closebreeding to mild linebreeding. From a genetic viewpoint, inbreeding results in an increase of the number of homozygous gene pairs in the offspring. Homozygous refers to a condition where two paired chromosomes have the same allele (gene type) at a corresponding point. Because two close relatives tend to have more of the same alleles than two unrelated individuals, their mating provides a greater chance for identical alleles to be paired with their offspring. Perhaps the greatest advantage of inbreeding is that it increases the prepotency of individuals within a herd and consequently helps to create distinct true-breeding strains or families. The prepotency (the ability of a stallion or broodmare to stamp desirable characteristics upon their offspring with a high degree of predictability) is the result of the parent being homozygous for important desirable traits. When such a parent carries two identical alleles on corresponding points of a chromosome pair, he transmits that allele to the same chromosome point within his offspring. If two such parents are mated, the offspring will always possess the same desirable trait, as Mount Royal King has proven to do. Inbreeding increases homozygosity as it increases prepotency.

Inbreeding also exposes certain weaknesses within the inbred herd. Uncovering these undesirable traits can be an important tool for the overall improvement within a large breeding program. By carefully eliminating inbred individuals which show inherit weaknesses; the breeder can slowly remove any undesirable recessive genes from the herd.

You will find that vigor and fertility are actually improved when inbreeding is accompanied by careful selection. As with the high possibility of defective genes being inherited by and through inbreds so also comes the higher possibility of “superior” genes being inherited by and through inbreds. An inbred will CONSISTENTLY reproduce himself and if that individual is superior then he will out produce the hybrid or any other type of pedigreed horse consistently whatever he is bred to, and will excel in the breeding barn when linebred, in that he will consistently reproduce himself EVERY time. Mount Royal King definitely does that.

A note of interest on inbreeding… Horses have millions of genes on 64 chromosomes or 32 pairs of chromosomes. From one matched pair of chromosomes you have millions of matched genes, which is why only one matched pair or an inbreeding coefficient (IBC) of +3.33% would give an animal the ability to throw “set characteristics” with each breeding, whether it is linebreeding or outcrossing. Mount Royal King has 10 matched pairs of chromosomes and an IBC of +32.50! Using only one gene as an example, each breeding a horse contributes one gene at a specific location on one chromosome of a pair of chromosomes. We do not know which chromosome of the pair the gene will come from. If the gene contributed to the foal is a “matched” gene which means the exact same gene at a specific location, then it doesn’t matter which chromosome the gene comes from because the genes are identical. If the gene is NOT a matched gene then you will have a 50/50 chance with EACH breeding (each breeding is a new roll of the dice) that any specific unmatched gene will be thrown Horses with “shotgun” pedigrees or no common ancestors have a mathematical calculation of throwing approximately 16 billion different combinations of their gene pool. If these shotgun bred horses are outcrossed, the full siblings from these non-inbred horses can be totally unrelated or have NO similar genes.

I hope this information is interesting and helpful in your search for a stallion. Good luck in your search. If you have any questions, do not hesitate to contact me.


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