Animal Breeding the Influence of a Previous Impregnation
Animal Breeding the Influence of a Previous Impregnation That the succeeding progeny of the female previously impregnated, does in some instances possess resemblances to the male by which she was thus impregnated cannot be gainsaid. The instances in which it has been noticed have been so many and the resemblances have been so marked that they cannot be ac- counted for in any other way than by attributing them to the influence of such impregnation.
On the other hand, the instances in which such resemblances cannot be traced are also numerous. As the different results that follow such impregnation cannot positively be determined beforehand, the whole question is obscured by the uncertainty of the results.
Enough, however, has been gleaned from observation and other- wise, to make it clear to the breeder of high-class stock, that to breed thus is always attended with an element of hazard, since it may introduce into the progeny variations that are not desirable.
The Influence of a Previous Impregnation Defined. —The defining of this question has been in a manner anticipated in what has just been said. In more precise language, it may be said to mean that in the process of procreation, the influence of the male sometimes extends to the offspring of the female by another male. The fact, as already intimated, has been abundantly established by observation.
The instances in which it has so occurred have been numerous, not only among the lower animals but also in the human family. So marked has this influence been that it has in many instances proved a source of serious loss to the breeders of pure-bred stock.
Especially has this been the case when certain color markings are required as evidence of purity of breeding.
Illustrations of the Influence of a Previous Impregnation. —The recorded instances of such inheritance are so many that the only difficulty found is in choosing between them.
The following have been selected: —
- In the Royal stud at Hampton Court, England, it is stated on the authority of Goodale, that several colts were dropped in one year sired by the thoroughbred stallion Acteon, but which had the markings of the thoroughbred stallion Colonel to whom the mares had been bred the previous year. These markings consisted of a white hind fetlock and a white mark or stripe on the face. Acteon had no white markings.
- The same authority states that Mr. A. Morrison, Bognie, Scotland, had a superior Clydesdale mare bred to a Spanish ass in the year 1843. The progeny of course was a mule. She was subsequently bred to a horse, with the result that the progeny so closely resembled a mule that parties who saw it at a distance took it for a mule. And what is even more remarkable this animal inherited in a marked degree certain attributes of the mule, as for instance endurance.
- Miles records from his own observation the case of a Chester white sow, owned by the Michigan State Agricultural College, which had been bred to an Essex boar, and the following year was bred to a pure Chester white boar. The pigs were all more or less spotted with black. This could be accounted for in no other way than through inheritance from the Essex boar, which is of course black.
- Professor Agassiz states that he coupled a Newfoundland bitch with a water dog and subsequently with a greyhound. The progeny from the second mating bore a close resemblance to the progeny from the first, which were a mixture of Newfoundland and water dog with scarcely any resemblance to the greyhound.
- This influence has also been detected in many instances in the close resemblance which children by a second husband have borne to those by the first husband. This has been especially noticeable in the children of white parents when the mother had previously borne one or more children to a negro father.
The children subsequently begotten by the white father are in many instances darker in color than other white children, and they also frequently have certain features of the negro.
The Influence of a Previous Impregnation May Extend to Successive Births. —In some instances, the influence of a previous impregnation extends to the progeny of several births successively by the same mother.
The following illustrations are select- ed:—
- Shaw of Leochel-Cushnie, Scotland, as recorded in the Farmers’ Magazine, had six pure Black faced ewes bred to a pure Leicester ram. Other Black faced ewes were mated with a Down ram. The Black faced ewes were all horned. The producers was of course crossbreds and showed more or less the characteristics of sire and dam.
The next year all the Black faced ewes were bred to a pure Black faced ram. The progeny had brown faces and were hornless. When mated a second time with a Black faced ram, the progeny showed less resemblance to the Leicester and the Southdown than they did the previous year, but two of the produce were still polled, one was dun faced like the Southdown and had small horns, and three were white faced like the Leicester.
- Mr. Geo. T. Allman, of Tennessee, testifies that he bred a pure Berkshire sow successively to a pure-bred Berkshire boar, and in every instance the progeny had little or no hair, in this respect resembling a Neapolitan sire, with which she had been first mated. The Country Gentleman records the testimony of Mr. A. W. Frizzell of Maryland which in summary is as follows ‘: He had a pair of prize-winning Dark Brahma fowls which were inadvertently mated with pure White Brahma cocks, and with the result that three years hence White Brahma markings still manifested themselves in the progeny.
Instances are also on record where pure-bred mares bred to an ass and subsequently mated only with pure bred stallions of kindred blood, never again bred true to type. On the other hand, it is also true that in many instances of breeding, similar in kind, like results have not followed, that is to say, the females that have thus been coupled with males of another breed do again breed true to type.
A First Explanation of the Influence from a Previous Impregnation. —From the instances cited, and from a great array of other instances that may Be cited, it cannot be doubted that the influence of one impregnation does frequently extend to the progeny from succeeding impregnations. Three explanations have been offered which will now be submitted, but no one of the three is entirely satisfactory. The first submitted, however, is more so than either of the others.
The first explanation of the influences under consideration supposes that the mother has been impressed with the paternal characteristics of the fetus during its intra-uterine existence, that is to say, that the blood of the female has imbibed from that of the male through the placental circulation some of the attributes which the fetus has derived from the male parent, and that the female may communicate these with those proper to^ herself to the subsequent off- spring of a different male parent.
Dr. Carpenters and others have advocated this theory. This explanation is the most satisfactory that has yet been offered of the reasons for the influence under discussion. It does not seem unreasonable nor contrary to the laws of physiology. If correct, it not only furnishes an explanation of the resemblances in the off- spring from a different male to that from a male different previously coupled with the mother, in the first birth that follows such coupling, but also in succeeding births where such resemblances continue to manifest themselves.
Where they do, it has been noticed that they become less pronounced as time goes on. This is just what would be expected, as the attributes of the male thus imbibed, as explained above, would in the absence of renewal, naturally be- come obscured by the attributes proper to the female which are continually being’ renewed by the processes which sustain life.
But the objection has been raised, on the ground that similar influences have been observed in fowls where the egg is separated from the mother before the incubating process begins. The core of the objection raised is found in the fact, that during the entire process of incubation, in which the materials furnished by the mother fowl in the egg are being transformed into new life, the entire process goes on entirely separate from the mother.
Because of this, it would seem impossible that during the process its character could be in any way influenced by her. The plausible answer, however, may be offered to this objection, that the attributes of the male may have been imbibed through the circulation, while the egg was in process of development.
A Second Explanation of the Influences From a Previous Impregnation. —A second explanation sup- poses that the impregnated ovum impresses its own characters on the mass of the decidua, and through this on the maternal placenta, and that the maternal placenta in turn impresses its characters on the decidua and embryo of the next succeeding generation.
The objections to this theory are, that the placenta and decidua are temporary organs that disappear at the time of parturition, or within a short time subsequently, and that the mucous membrane itself is removed and replaced with new tissue. It is possible, however, that the new mucous membrane formed to take the place of the old one may in some ways have been impressed by the former which it replaces.
On the principle that adjacent cells do tend in some instances to ingraft their plastic or formative powers upon each other, the new mucous membrane may have become impressed more or less by characters of the one which it supplants, since the former begins to appear some time before the latter is removed; in the human family as early as the eighth month of pregnancy.
It would seem impossible, however, to apply this theory to fowls, as Miles has intimated, when the embryo is separated from the mother during incubation.
A Third Explanation of the Influences From a Previous Impregnation. —A third explanation of the influences from a previous impregnation claim that through the tendencies of habit the female reproductive system is inclined to repeat strongly marked characters which it may have produced. It has been observed that impressions transmitted by males of the purest breeding are the most marked on the future progeny.
For instance, the influence from mating an ass with a mare is more far reaching on the succeeding progeny from stallions to which the mare has been subsequently bred, than would be the case had the mare been bred to a stallion of another breed rather than to the ass. Likewise, the influence of a Gallo- way sire would be more far reaching on subsequent progeny than the influence from a grade sire.
It has also been observed that in some instances all the succeeding progenies are more or less affected by the first impregnation, but that the influence traceable is usually less and less pronounced as subsequent breeding from the same female progresses. It is easy to understand why intensity of breeding should more powerfully affect the sexual system of the females, but on the recognized principle that habit is usually strengthened with repetition, why should not those influences which first gave bias to the sexual system in a certain direction grow stronger rather than weaker?
The argument therefore that these influences result from habit is not satisfactory. The Intensity of the Male Element in Fertilization Differs Widely. —The intensity of the influence of the male element of fertilization upon the ova seems to vary widely in distinct species, and also in animals of the same species. In many species of fowl, a single act of copulation is sufficient to impregnate a number of eggs, while in other species a repetition of the act is necessary. In the hen, for instance, eggs are fertile from four to sixteen days after the act of copulation, while with turkeys a single act of copulation is sufficient to impregnate all the eggs of one laying.
It has even been claimed that in some instances the single act of copulation will fertilize the eggs of a second period of laying. But it has been noticed that incubation is not so satisfactory nor are the young birds so strong and vigorous as when the male turkey mates more frequently with the female.
Agassiz states that certain varieties of turtles which begin to copulate at seven years do not begin to lay eggs until four years later, and copulation twice a year seems thenceforth necessary to fertilize succeeding sets of eggs.
Impregnation therefore is a question of degree, and this may at least in part account for the influence of a previous impregnation upon impregnations that follow. It has been noticed that, in some instances at least, the whole female sexual system is thus impressed when the male animals used in breeding are from any cause deficient in bodily vigor.
Then it is, that when the reproductive energies of cocks have been overdrawn upon, through overmuch mating, the hatching process which begins is never completed because of inadequate fertilization.
In other words, the sexual system of the female has been so feebly influenced, that it does not properly perform the function of which it is capable through strong impressions made upon it by the male element of fertilization.
Fecundation Sometimes Affects the Whole System. —It is very probable, therefore, that the act of fecundation does, in some instances at least, affect the entire system, and more especially the whole sexual system, hence, the ovary to be impregnated afterwards is so modified by the first act, that later impregnations do not efface the first impressions.
This theory finds support in analogous observations made with reference to plant fertilization. Darwin inclines to the belief that in such fertilization the male element not only affects the germ, but also the surrounding tissues of the mother plant, and that therefore the male element acts directly on the reproductive organs of the females, and not simply through the intervention of the crossed embryo. If it is true, therefore, that the sexual system is influenced by impregnation then it follows that traces of such impressions may show themselves in progeny from subsequent impregnations.
Influence Greatest from a First Impregnation. —It seems probable that the influence of the male upon succeeding impregnations by other males is more marked in the first impregnation. General observation most assuredly gives countenance to this view, and the influence is greater in proportion as the male used in fertilization is prepotent.
Such a result may arise, first, from the greater impressibility of the sexual system when first capable of being impregnated, on the principle that youth is always more plastic and therefore more easily impressed than age.
In other words, impressibility lessens with the increase of the impressions already made. In the second place it arises from the power which the potent sire must impress. The counter fact, however, should not be lost sight of, that in many instances a previous impregnation makes no perceptible influence on the progeny from succeeding impregnations.
This may arise from the greater potency of the female to resist impression on the part of the male of another breed that may have been coupled with her.
This phase of the question does not seem to have been much discussed, if indeed at all, hence, evidence bearing on the question does not seem to have been collated.
Practical Bearing on Stock Breeding. —The practical bearing of this question on stock breeding is very direct. It follows, first, that it would be very unwise to use valuable pure-bred females for purposes of cross breeding, if they are again to be used in breeding pure breeds. As has been shown, there is probability that they may not again breed true to type.
In other words, when pure females have been used in crossbreeding they should not, as a rule, be again kept for producing breeding animals of the same pure breed. It follows, second, that young females especially should not be thus crossed, because of the greater certainty that they will not again breed true to type.
And it follows, third, that young females especially should be carefully guarded from impregnation through inferior or ill-bred sires. In other words, it follows that inferior sires should be shunned because of the influence that they may exercise upon succeeding impregnations as well as upon the immediate progeny. But it is fair to concede, that the influence from a sire of mixed breeding upon the progeny from subsequent impregnations is likely to be less than that of a sire vigorous and purely.
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