Animal Breeding - Prepotency

By Thomas Shaw

The question of prepotency is of great practical moment to the breeder of live stock, because of the direct influence which it has upon improvement or the want of this, in a stud, herd , or flock. Like many of the features of breeding it is only understood in part, but happily enough is known regarding it to enable the skilled breeder to choose animals possessing it with a reasonable degree of certainty.

Prepotency Defined. – Strictly speaking prepotency is the superior power which one parent has over the other in determining the character of the offspring. But the term is more commonly used to indicate that power which an animal has to transmit its own qualities. Sometimes prepotency is general, having reference to breed, race, or species. When it is said that a breed is prepotent, it is meant that animals of that breed are all possessed of much power to transmit the characteristics of the breed. In other instances prepotency is special, having reference to the individual. When an individual is said to be prepotent, it is meant that it has much power to transmit its own qualities to the offspring, that is to say when two animals are mated the parent possessed of superior prepotency will transmit in a greater degree than the other its own properties to the progeny. The great value of such power when breeding animals, especially in males, will be at once apparent.

Prepotency of Breed. – Prepotency of breed or race is clearly brought out when two distinct breeds are crossed. The offspring will more nearly resemble the breed possessed of the most marked prepotency. There is a great difference in the prepotency of breeds as such. The Galloways among cattle are noted for their prepotency. When crossed upon other breeds and especially upon grades, the progeny are nearly all black and hornless. Similarly, the American Merino among the breeds of sheep have a great power to transmit the characteristics of the breed to the progeny when crossed upon other breeds and more especially when crossed upon the grades of these. The mule, the progeny of the ass and the mare, is possessed of more of the features and characteristics of the male parent. The cause, as is further shown below, is the same in each instance, viz., the long periods during which these animals have been bred pure. Breed prepotency is also shown in the quick transformation of the common or mixed classes of animals to the type of the breed from which the males have been chosen. All breeds will not effect transformation with equal rapidity, since all are not equally prepotent. The most prepotent breeds will, of course, effect such change the most quickly. And they will effect it more quickly on animals much mixed in breeding than on those more highly graded.

Individual Prepotency. – Prepotency in the individual is shown in the closeness of the resemblance in the progeny to the parent and to one another. The second result mentioned is, of course, effected by the same influences as produced the first, and is one of the strongest evidences of prepotency in the individual, since it shows in a marked degree the power of the one individual animal to transmit its own individual characteristics to the progeny, though mated with different individuals. These will of course, be possessed of different degrees of prepotency. The power of the one animal so to overcome these as to produce a progeny that closely resemble one another is the highest evidence of prepotency. And each animal added to the list of such progeny is an additional evidence of prepotency. The greater the diversity in the parents of the progeny thus assimilated, the stronger is the evidence of prepotency in the one parent of the opposite sex which has effected such assimilation. Prepotency is usually more manifest in males, for reasons given below in the paragraph which discusses prepotency especially important in males, but it may also characterize females as well as males. Instances are not uncommon in which the resemblance between the different members of one family is so close, that family resemblance may be readily traced from such resemblance, and it has been inherited from the mother.

The evidences of prepotency are usually more clearly apparent when the resemblance is manifest in the offspring of animals of the same pure breed or of different pure breeds as contrasted with grades. For instance, if a pure male in one instance were to beget progeny from females of the same breed which bear a close resemblance to the male parent, this result would be a stronger evidence of prepotency in the male than a similar result produced by mating him with females of mixed breeding, since the resistance to modification in the progeny of the females in the first instance would be stronger than resistance to the same in the females in the second instance. And if there was a close resemblance in the progeny of pure females of different breeds, not stronger evidence of prepotency in the males could be furnished, since in these instances his potency had had to effect change when resistance was both strong and diverse in character. In rare instances, however, the reason wresemblance in the progeny to one of the parents may be traced in grades. The hy those instances are rare arises from the lack of dominant properties which characterize grades because of the mixed character of their breeding.

Influences that Produce Prepotency of Type. – The following are chief among the influences that produce prepotency of type or breed, viz., the duration of the period during which the animals have been bred pure, and the inherent vigor of the type, race, or breed. The fact has been noticed as stated previously in Chapter III, that animals whose pure breeding is of great antiquity transmit their properties with more certainty than those of breeds formed within a comparatively recent period. Galloway cattle, for instance, transmit their properties with more exactness than Aberdeen Angus cattle. The progeny which is the outcome of a Galloway crossed upon grades, will more uniformly inherit the black color and the hornlessness of Galloway sires, than the progeny of Aberdeen Angus sires crossed upon similar grades.

The progeny of American Merino rams crossed upon grades will more surely inherit the form and properties of the Merinos, than will the progeny of Oxford Down sires crossed upon grades inherit the properties of the Oxford Downs. Similarly the progeny of Yorkshire swine crossed upon grades will inherit the properties of the Yorkshires more than will the progeny of Poland Chinas thus crossed inherit the properties of Poland Chinas. The progeny of the Yorkshires will be almost uniformly white in color that of the Poland Chinas will be variable in color. The reason is the same in each instance, that is to say, the Galloways, the American Merinos, and the Yorkshire breeds have been bred pure for a longer period than the Aberdeen Angus, the Oxford Down and the Poland China breeds.

But it is probable, as previously intimated, that there is a period when antiquity of breeding will cease to add to the prepotency of animals, that is to say, it is not certain that an animal from ancestry bred pure for five hundred years will be less prepotent than an animal from ancestry bred pure for one thousand years. It is not known, however, where antiquity of breeding will cease to add to potency in breeding. It is probable that the time will vary with varying conditions. Inherent vigor of type, race, or breed is a powerful factor in determining prepotency in the breed as it is in the individual. The reasons doubtless rest upon the acknowledged superior transmitting power which strength has over weakness and stamina over the want of stamina. This in part accounts for the superior transmitting power of Galloway cattle, Merino sheep, and Yorkshire swine.

Influences that Produce Prepotency in the Individual. - The following are chief among the influences that affect prepotency in the individual, viz.: Purity of blood, strong constitutional development, and in-and-in breeding. Purity of breeding and duration in the same strengthen prepotency in the individual as they do in the breed or race. They strengthen prepotency because they make and maintain dominance in properties. Each increment of alien blood introduced becomes a disturbing factor to fixedness in properties, and, therefore, it becomes a disturbing factor to certainty in transmission. On the other hand each generation of pure breeding adds to dominance in properties till these become so dominant that further improvement in that direction may not easily be made. Because of this the unwisdom of using grade, cross bred, or scrub sires or any other sires not purely bred will be at once apparent. The reasons why strong constitutional development strengthens prepotency in the individual as also in the breed or race are the same. They come from that inherent mastery which strength has over weakness. This explains why breeding from animals in the meridian of vigor, that is to say, neither young nor old, gives a progeny superior to those bred from animals immature or declining through age.

The room for selection on the lines of vigor is far greater in the individual than in the race, because of the many individuals in the race or breed as compared with the fewness of races. Vigor in the individual, therefore, can be turned to more practical account than vigor in the race. In-and-in breeding aids prepotency because it strengthens dominant properties. The more inbred animals are, them more intense their power to transmit such properties as they possess. This explains why the masters in forming breeds almost resorted to in-and-in breeding for a time when they were doing this. It also shows the wisdom in some instances of giving the preference to desirable sires that are more or less inbred and that are at the same time possessed of much bodily vigor. These three influences acting in conjunction should give the highest prepotency attainable.

Minor influences that Affect Prepotency. – Prepotency is influenced more or less by certain minor influences, as,

1. The existence of what may be termed secondary sexual characteristics. Sebright bantams with the perfect hen-formed tail in the males are less productive than those with a tendency to the development of sickle feathers. Rumpless fowls with the tail entirely wanting are much prone to lay infertile eggs, and sires with what may be termed a feminine head are rejected by skilled breeders, since it has been noticed that they prove less satisfactory as breeders.
   
2. The limitation to one sex of the power to transmit certain characters. For instance, it has been ascertained that in some instances only males, and in other instances only females, transmit certain forms of disease, at least for a time. The claim has also been made, based on certain statistics, that some diseases as consumption, for instance, are more readily inherited in males from the male parent, and in females from the female parent.
   
3. The lack of affinity in certain characters which makes it difficult to blend them. These make the influences that modify and tend to unify stronger than when there is more of affinity between alien properties. The causes of variation are seldom well understood. The fact, however, has been noticed, that animals of known prepotency will beget much more of resemblance to themselves in the progeny resulting from a cross upon certain pure breeds than upon certain other pure breeds.
   
4. By the effects of a previous fertilization of the mother. In certain instances it has been noticed that when a female of a certain breed produces by a male of another pure breed, and is then bred to a sire of her own breed, she does not always breed true to type. And in some instances females thus mated have never bred quite true to type again. But this question is further discussed in Chapter XIV. Here then are elements that disturb prepotency, but they do not disturb it equally nor so seriously as to make breeding a game of chance.

Animals Similarly Bred may Differ much in Prepotency. – That animals similarly bred and possessing precisely the same blood elements frequently differ widely in the degree of the prepotency which they possess has been noticed again and again, hence, there is not absolute guaranty of prepotency in near relationship. Many instances could be cited in support of the statement just made. In few of these has the contract in prepotency between animals bred just alike been more apparent than in the thoroughbred horses, Touchstone and Launcelot. Stonehenge records of the progeny of the former, that they showed much uniformity of color and below mediocrity on the turf. These horses were full brothers. Instances have come under the observation of the author in which pure bred males have been purchased, because of prepotency and good breeding qualities in members of the same family, which were quite disappointing. The conclusion must not be reached, however, that similarly in breeding is no guaranty of prepotency, for in other instances several, if not, indeed all, the members of the same family have been noted for their prepotency. It is simply not an absolute guaranty. Nor can prepotency be absolutely assured, as being the outcome of any particular method of breeding, as instances have been found in which highly inbred animals have not been prepotent. Again, some animals are prepotent, if the term may be thus used, in transmitting the qualities of their ancestors rather than their own. This accounts for the fact that some sirs not possessed of sufficient finish themselves to enter the show ring, have proved noted sires of prize winners. Such was the great stock bull, Knight of Warlaby (29014) owned by J. & R. Hunter of Alma, Ontario.

Rules Governing Prepotency not easily Framed. – The difficulties which surround the subject of prepotency are emphasized by what has been said in the preceding paragraph. Because of these difficulties it is impossible to formulate rules which govern it. But, as previously stated, purity of breeding and indications of bodily vigor taken together furnish a strong guaranty of its presence. These are, indeed, the most tangible guaranties of prepotency that can be furnished before it has been proved by actual test. It is also true that marked prepotency is likely to be transmitted, at least in degree. If that were not true the first great law of breeding would not be to the breeder a reasonable safe guide. An animal, the progeny of prepotent ancestry, is certainly likely to be more prepotent than an animal whose ancestors have not been prepotent. There is also a close interdependence between prepotency and in-and-in breeding. But when practiced by those not well skilled in the art of in-and-in breeding, it can scarcely be reckoned as a factor in choosing prepotent sires by the average breeder. On the other hand it has been used as an aid in producing some of the most prepotent sires that have ever existed. But this result has only been secured by skilled breeders.

Prepotency in Animals Inferior Individually. – Prepotency somewhat marked is sometimes found in animals inferior in individual characteristics, and in those with a strong bias to certain forms of disease, and the more pure the breeding the more likely is such prepotency to be found. Because of this, there is always much hazard in using sires possessed of inferior individual qualities. In breeding pure breds some inferior specimens will appear, even when the work is wisely and skillfully conducted. When those animals are offered for sale for breeding purposes, they are usually held at reduced prices. Those who are about to introduce pure bred sires into their herds, it may be for the first time, are much prone to invest in those inferior specimens, because of the comparatively low price at which such animals are offered. It would appear that such purchasers expect pedigree to make up for interior individual merit. The effect may be just the opposite. In fact, it is likely to be, as a result of the first law of breeding. Because of this hazard it is considered safer to breed from high grades of superior individuality than from pure breds of inferior individuality. There is the chance, however, that the individually inferior pure-bred parent may transmit the qualities of an ancestry superior to themselves, but that such transmissions will follow is far less probable than that the transmission will take after the parents. Inferior individuals, therefore, however purely bred, should not be bred from.

Marked Prepotency not of Great Frequency. – Very marked prepotency is not of great frequency even in pure-breds. Of this fact no stronger proof can be furnished than that which comes from the “Grasmere” herd of Shorthorns located near Lexington, Kentucky. This herd was founded in 1831, and was owned and personally supervised by Mr. William Warfield, the author of “Cattle Breeding” and probably without a peer in the knowledge of the rules that govern breeding. Mr. Warfield testifies that during fifty-seven years of the existence of this herd, of twenty-seven sires used, only five or six of the entire number possessed prepotency in a marked degree, although without exception they had been chosen on principles that were likely to insure prepotency as far as these principles are known.

Each pure breed has its list of sires of outstanding prepotency but the list is not a very long one. Some of these animals were wonderfully impressive in their day, howsoever mated. So famous were they as sires that breeders to this day frequently refer with pride to the fact that animals owned by them trace to these potent sires, even after the lapse of one hundred years and more. But those who do thus would do well to remember that with animals as with men, too much may be made of memorable ancestry. The value of such blood may have been greatly neutralized by subsequent breeding. But even though not thus weakened, it can only be present in an infinitesimal degree except where more or less of continued in-and-in breeding has been practiced.

Prepotency Specially Imported in Males. – The prepotent quality is specially important in males, owing first, to the much greater influence which they exert relatively and absolutely in the stud, herd, or flock, and second to the use that is made of them in the improvement of all classes of stock, hence, all the great breeders aimed at choosing their males from sub-families more highly inbred than the average of their stock. When but one males is used in a stud, herd or flock his influence on the progeny is equal to that of the sum of the influence of all the females combined when the individual excellence and prepotency of each female is on a par with that of the male. When, however, his individual excellence and prepotency are greater than that of each female, his influence on the progeny will be as much greater than that of the combined influence of all the females as his individual excellence and prepotency exceeds theirs. The importance, therefore, of choosing sires of the very highest excellence and prepotency cannot easily be overestimated. If the desired prepotency can be obtained without in-breeding it is usually preferable to have it so, but marked prepotency is more frequently found in animals more or less inbred.

Prepotency not Assured until Proven. – Prepotency in a sire is not assured nor can it be, until it is proved in his progeny. All the requisites may be present that tend to assure prepotency, and yet it may not be represent in a degree that is satisfactory. Because of this a young sire should be used cautiously at the first, that is to say he should be mated with only a limited number of high bred females until evidences of his prepotency are furnished in the progeny. To mate a male whose prepotency is unproved with all the females in the stud, herd, or flock, would be a hazard which no breeder of valuable, pure bred stock can afford. But as soon as it has been ascertained that a sire is prepotent the most should be made of his presence by using him to as great an extent as is practicable, but not to the extent of shortening the period of his usefulness.

A sire in the meridian of vigor, whose prepotency has been proved, is a far safer investment than a younger sire equally good but whose prepotency has not been proved. And yet in choosing sires the rule with many is to purchase the latter in preference to the former. Valuable sirs that are markedly prepotent should never be discarded until they have passed the meridian of their usefulness. If the owner must make a change to avoid in-breeding, some one else should secure the prepotent prize. The value of a markedly prepotent sire, many of whose progeny are good enough to win prizes in leading show rings cannot be easily overestimated. There have been instances in which the possession of one such animal has brought competency to the owner.