Animal Breeding Fecundity
Animal Breeding Fecundity The relation between the breeding properties of animals that are kept for breeding and the profits arising therefrom is both intimate and close.
No sooner has an animal reached the proper age for breeding when kept for that purpose, than the relative profit from keeping it grows less than it would other- wise be, every day that it is kept subsequently with- out discharging, at least in reasonable degree, the breeding function.
And this is more especially true of animals that are kept chiefly for the milk that they provide. It is important, therefore, that every attention should be given by those who keep domestic animals to the maintenance of a high standard in productivity in the stud, herd, or flock.
Fecundity Defined. —Fecundity means the quality of bringing forth offspring freely, regularly, and in many instances abundantly. It means about the same thing as prolificacy when the latter is applied to animal breeding, but prolificacy is the broader term and therefore has a wider range of application. Fecundity has reference to frequency in reproduction as well as to the numbers produced.
Of course, in those classes of animals which produce but one at birth, it can -only have reference to frequency and regularity in production. In such instances the most fecund animals will be those which produce the most freely and regularly from the time that breeding should begin.
But when more than one is produced at birth, the most fecund animals will be those that produce the most freely and regularly, and that bring forth most numerously at each season of parturition. It will be noticed that this property is the attribute of females only, but it is doubtless influenced by the males used in service. It differs from fertility in that it has reference to the numbers produced rather than to the ability to produce.
Fertility is of varying degrees, but an animal that is susceptible of impregnation is fertile. It is the opposite of sterility and barrenness in females. Females that breed irregularly and infrequently are commonly spoken of as shy breeders, and males that are unable to beget are spoken of as impotent.
Influences that Affect Reproduction. —The reproductive powers of animals are much influenced by changes in their surroundings and habits and by the modes of life to which they are subjected. All such changes as tend to equalize conditions are favorable to reproduction.
For instance, when regular supplies of food supplant those where food has been in excess a part of the year and insufficient another portion of the same, the influence on productivity is favorable, and so of all other influences that tend to equalize.
Regularity even in the habit of breeding tends to perpetuate such regularity. But the results are ad- verse when the changes in themselves are unfavorable to the healthy action of the system. The African ostrich, for instance, has been transplanted to certain other countries -where the surroundings are considered less favorable than in South Africa, and with the result that there has been a decrease in productivity. The influences that affect productivity favorably and adversely are much the same as those that affect fecundity similarly, and they are given below.
Influences that Affect Fecundity Adversely. — The following are chief among the influences that affect fecundity adversely:
- Confinement and lack of exercise.
- Irregular supplies of food and lack of uniformity in conditions.
- Food lacking in succulence or containing too much sugar.
- A plethoric condition of the system.
- Meager milk production. And
- In-and-in breeding, line breeding, close breeding, excessive breeding, and in some instances heredity.
These influences may act singly or in conjunction. The more they act in conjunction the more adversely they will influence fecundity. They will now be considered in detail.
Influence of Confinement on Fecundity. —Fecundity is affected adversely by confinement and the lack of exercise which confinement brings with it. This may be shown in many ways. It is seen in the relative frequency of impotency in males and of barrenness in females among domestic animals that have been much confined.
To so great an extent has this fact been recognized by breeders that they invariably adopt some measures whereby such exercise can be obtained for breeding animals. Paddocks are provided for those which may not usually run with the females, and pastures of extent are provided for females which must needs be kept on the soiling system.
Devices are sometimes resorted to which shall compel the animals to exercise, such as, for instance, when bulls and stallions are made to work. In the human family the relation between a life of labor or the opposite on reproduction is sharply drawn. Large families are usually found only among the classes who toil.
It is seen in the impaired or destroyed powers of reproduction in wild animals when deprived of their liberty and in the inability of their offspring to breed. Animals once wild and confined, as in a menagerie, breed very shyly and when they do, in but a few instances beyond the first generation.
The males become impotent and the female’s barren. The same principle has also been demonstrated, as stated by Darwin, in certain experiments conducted with fowls in France. These were given different degrees of liberty.
The fecundity increased with the increase of liberty given to the fowls, at least, up to a certain limit.
Influence of Food Supplies and of Conditions on Fecundity. —Irregular supplies of food and lack of uniformity in conditions affect fecundity adversely. This has been shown in the shy breeding qualities of the Spanish Merino sheep in its native country as compared with the same in other lands.
In Spain prior to the present century the traveling flocks were oftentimes on short supplies, especially when journeying to and from the mountains. The conditions otherwise were uneven, as, for instance, when exposed to adverse weather. When those sheep were first brought to the United States their want of fecundity was distinctly noticeable. Since that time their breeding qualities have improved, especially on arable farms where they can be given regular supplies of suitable food and subjected to uniform conditions.
On the western ranges not only Merinos but also other breeds of sheep breed more shyly than when suitably cared for on the farm. It is also shown in the less prolific character of the mountain breeds of sheep as compared with those of the lower land.
It would not be easy to give statistics that would form a just comparison, hut the fact has been noticed to the extent of being commonly recognized by those who are acquainted with sheep husbandry.
The reasons for the less fecundity of the mountain breeds are remarkably similar to those which explain the same in range flocks. It is further shown in the greater fecundity of domesticated animals as compared with the same when wild, as instanced in pigeons, geese, and ducks, rabbits, dogs, swine, and other animals.
Some varieties of pigeons breed but twice a year in a wild condition, and when domesticated the same varieties will breed much oftener. Swine seldom breed in the wild state and produce but few at a litter. Under domestication they may be made to produce litter regularly twice a year and of about twice the number in each litter produced by the wild species. The increase in the prolificacy of tame rabbits as compared with wild ones is even more marked.
Influence of Nutrition on Fecundity. —Nutrition materially affects the activity of reproduction, since it supplies the organs of the latter with materials concerned in its operations. If these materials are in- sufficient or unsuitable the generative powers suffer accordingly. Sometimes there is a certain degree of antagonism between the nutritive and generative functions, the one operating unduly at the expense of the other.
This antagonism always exists when the normal equilibrium of suitable conditions is disturbed, and this will be true let the disturbance arise from whatsoever cause it may. It may not always be easily possible to tell just where this equilibrium lies. It is to be gathered from cumulative experience and observation.
Any excess in the nutritive activity of the system acts prejudicially on the powers of reproduction as shown in the partial or total sterility of fat animals, over-luxuriant plants and nut bearing trees.
Animals that have been made excessively fat for show purposes are usually indifferent breeders. To so great an extent has this fact come to be recognized that it affects their sale adversely for breeding uses. Many of them breed irregularly and produce progeny lacking in size and stamina at birth or do not breed at all. But poor breeding qualities are less frequently found in show animals kept in uniformly high condition from birth than in those subjected to alternations of high and low conditions.
In over-luxuriant plants and nut bearing trees the energies of the plant and of the tree are so concentrated in the production of stems and leaves in the one case, and of wood in the other, that little or no fruit is produced. The opposite is also true, namely, that any marked deficiencies in nutrition impair and hinder breeding properties and, in some instances, destroy them altogether.
This finds ample illustration in the decline of life. The nutritive processes weaken with advancing age till at length these cannot sustain the generative function in the male or the reproductive function in the female, until impotency is produced in the former and sterility in the latter. Certain forms of disease lead to comparable results, especially those forms which seriously impair nutritive function.
The intimate relation between abundant food- supplies and the judicious feeding of the same may be further illustrated in many ways. Cows regularly supplied with enough suitable food will breed at almost any season of the year.
Those kept on nutrition’s food in the winter and on good pastures in summer will mate only in the summer after the grasses have become plentiful.
During the winter while on innutritious and dry food, the entire system languishes including the generative function. The rich and abundant pastures stimulate the whole being of the animal including the organs of reproduction. They at once become active.
Flock experts have found that when ewes whose lambs have been weaned are put upon rich pastures, they breed more quickly than when on poor pastures, and when the pasture is supplemented with some stimulating grain food, as barley or wheat, the tendencies to breed quickly are intensified.
The function of breeding is shared in the renovation of the system, hence, the stimulus given to the breeding impulse which leads to early mating. In this way more uniformity is secured in the time when the lambs are dropped, and more lambs are produced.
The bearing of suitable food, when suitably fed, on increased fecundity is thus very clearly shown. The wisdom of feeding ‘females liberal supplies of nutritious food when reduced in flesh through nursing their young when it is desired to have them breed quickly again will be at once apparent, as also the necessity for feeding males similarly when preparing them for active and prolonged service.
Stallions in charge of intelligent grooms are thus prepared for the mating season. When males are much used in service, they also require liberal nourishment. This explains why intelligent stockmen feed nourishing and suitable food freely to their sires during any seasons of breeding in which instances of mating are frequent.
It has been noticed that such treatment has a marked influence on ability to beget as well as upon increased numbers in the progeny begotten when more than one is produced at birth.
Influence of the Quality of Food on Fecundity. —The quality of the food exercises an important influence on fecundity. A substantial proportion of sugar in the same injures the reproductive functions. This arises, in part, at least, from the abundance of carbohydrate elements in such food. When fed in copious quantities and for a prolonged period it also tends to cloy the appetite. Foods rich in sugar stand in high favor with many who prepare animals for exhibition.
For such a use sugar is frequently fed in the pure form and it has been noticed that when thus fed freely to young animals their breeding powers are affected adversely, and the general tone of the system likewise suffers. A dry dietary is unfavorable to impregnation, and a rich, juicy and succulent; vegetation is favorable to the same.
A diet unduly lacking in succulence, as, for instance, hay long stored, is unfavorable to repro- duction when fed alone. Such a diet tends to induce a constipated condition of digestion and the breeding powers suffer in consequence. When, in addition to the dryness, the nutritive quality of the food is low, as when straw constitutes the food, the outcome is still more averse to breeding.
This explains why seasons of extraordinary drouth are unfavorable to fecundity. The grasses are both dry and innutrition’s. It is easily possible, however, to feed foods too succulent to get the best results from breeding. In sea- sons of excessive rainfall the grasses, though abundant, are not sufficiently nutritious, and frequently they keep the bowels in a condition too lax.
Foods rich, juicy and succulent are favorable to free and regular breeding. Richness in food furnishes the needed nutrition, juiciness tempts the appetite, and when the foods are also succulent, they act beneficially on the digestion. A fresh Dwarf Essex Rape pasture well matured, furnishes an excellent instance of a single food possessing all these properties in a marked degree.
A carbonaceous diet is also unfavorable to fecundity, while a nitrogenous diet is favorable. The carbonaceous diet tends to produce fat and heat, while the fetus during development is more in need of muscular sustenance. This is obtained from the elements of a diet nitrogenous in character.
Brood sows reared on a corn diet are shy breeders. When fed on the same during pregnancy the pigs are likely to be small and deficient in vigor at birth, and the danger is imminent that the sow may have trouble in farrowing. In the distinct corn belt such a diet has diminished the fecundity of swine.
A Plethoric Condition Diminishes Fecundity. —Diminished fecundity may arise from a plethoric condition of the system. Such a condition is accompanied by overloading with flesh, which begets sluggish tendencies in the whole being unfavorable to reproduction. It may also arise from congestion and inflammation in the organs concerned in procreation, induced, or at least aggravated by these influences.
The correctives for the first are, active exercise even though enforced, and a diminished diet, but the depletion of the system should be gradual. In this way the breeding powers of males that have become impotent and female’s barren through over high fitting for the shows have been restored. When organic dis- ease, however, is present in either of the forms named or in other forms, the most skillful treatment will often fail to remove the same.
When the Breeding Powers are Most Active. — The breeding powers are most active when animals are in what may be termed moderate condition as to flesh, and in the meridian of vigor. A marked tendency to lay on fat is frequently accompanied by a delicacy of condition and a diminished secretion of milk, as well as by a loss of fecundity.
The first comes from the sluggishness which it induces. The second results from the energies of the system being too much concentrated in the opposite direction, that is, in the production of milk. And the third is the outcome of the antagonistic influence of these causes acting in conjunction.
When breeding is rendered impossible, as by castration or spaying, the tendency to lay on fat is increased. This arises from the more restful habits of castrated or spayed animals and from the less extent to which the energies of the system are divided.
The moment that either operation takes place the generative function no longer requires to be sustained. Nor is milk production any longer, usually, possible in females. Castration and spaying are further discussed in Chapter XXIX.
Sterility in Fat Animals. —The immediate cause of sterility in fat animals frequently rests in what may be termed fatty degeneration. It is caused by the conversion of the albuminous or gelatinous materials of the tissues of the reproductive organs into fat. While in that condition reproduction is impossible.
In other instances, the tubes in females that convey the seminal fluid to the ovum fail to do so, they are so filled with fatty matter, hence impregnation cannot take place, howsoever vigorous the male may be. The mistake, however, must not be made, that a fat condition of the animals is incompatible with the ability to breed, since both males and females have gone through years of successful exhibiting without ceasing to breed with normal certainty.
In such in- stances, however, the animals have been high fleshed from the beginning and have been subjected to much uniformity of treatment. But the progeny, notwithstanding, are not often the equal of the parents in vigor or individuality. Long continued succession in the generations of great prize winners, at least in animals kept for meat, has never occurred.
The Relation Between Milk Production and Reproduction. —There is an intimate relation between the milk producing powers and those of reproduction. This is owing, in part at least, to the dependence of milk secretion on the mammary glands. These in turn are under the direct influence of the breeding organs, or they sympathize very closely with them, hence animals Avhich breed with the least difficulty, and which produce the most healthy and vigorous off- spring, usually yield the best supplies of milk among animals of that type.
The logical conclusions from these premises are, first, that it is quite possible in meat-producing animals to reduce the milk-giving function below7 what would be for the best results in breeding, and for the best maintenance of the progeny, and second, that mere selection in dairy herds based on abundant milk-giving should of itself improve the breeding qualities of the animals of the herd.
Regular breeding in meat-producing herds or flocks will therefore exist in the most marked degree when no little attention is given to the retention of milking qualities in the females. But in dairy herds it would be possible to stimulate the milk-giving function to react injuriously to the whole animal by reducing its vigor and consequently injuring both the breeding and milk-giving functions.
These results, however, are not a frequent occurrence. The proper sustenance of the animal during gestation also has an important bearing on milk giving and consequently on subsequent reproduction.
Many fear keeping the pregnant animal in a good condition of flesh during the period of pregnancy, lest there should be trouble at parturition. Such a fear is groundless, providing the food producing the flesh has been duly succulent and has had in it a sufficient proportion of protein. It is a mistake to have animals thin in flesh, beyond a certain limit, when they bring forth their young.
It is not fair to the progeny before birth, and it will react against abundant milk giving. If a female is low in flesh when her progeny is born, she is dependent entirely on food supplies for the milk that she gives. If she is in a good condition of flesh when her progeny is born, she has a residuum of milk-producing materials stored up in her own body which in time is turned into milk.
This explains why a brood sows in good flesh when her large litter of young are born is usually thin by the time, they are ready to wean. When the dam is low in flesh at parturition the drain upon the energies that follows reduces ‘her vigor. This reduction of vigor extends to the assimilative powers; hence she remains low in flesh during the milk giving period. Breeding powers through sympathy are also enervated, hence time is lost before the animal can be bred again.
The Influences of Over-Breeding of Heredity on Fecundity. —The term over-breeding is used here to mean breeding excessively breeding from relatives so close that injurious results follow. It also means breeding too young and too frequently. Reference has already been made to the adverse influence which in-and-in breeding, line breeding, and close breeding have on fecundity. (See Chapters X and XI.)
Immature breeding produces results similar in kind and usually even more quickly. When excessive it tends not only to reduce stamina, but to weaken seriously if not indeed to destroy the generative functions. Force a young child to walk before its limbs have strength enough to support it, and the limbs become weak and unshapely.
Encourage it to tax the brain unduly at too young an age and the clinger is imminent that it will become a physical and probably a mental wreck. So, when a sire is used in breeding at too young an age the whole being of the same is injured, including the generative organs. And when a female is bred too young, normal size in her is not likely ever to be reached. When she is bred too frequently the stamina of both the dam and progeny suffers.
The latter always suffer when the dam has been bred excessively. In many lines livestock has thus suffered from excessive breeding during recent years. But the greatest mistakes have been made by dairy farmers in breeding heifers too young, by some swine growers in breeding sows too early and by the growers of beef and mutton in the extent to which young sires have been used.
The first have to some extent been influenced by the desire to establish the habit of milk-giving in the young female so that the energies of the system would be encouraged to concentrate in that direction. The second have sought profit in trying to reduce the duration of the rearing period prior to the time of reproducing, and the third have been influenced by the low price at which old males must be sold when they cannot longer be used in the herd.
All have erred. Good breeders are opposed to breeding sows so as to reproduce under the age of twelve months, and to produce twice a year, to breeding ewes under the age of nineteen months, and to using young males with much frequency until they are quite beyond the age at which they become capable of begetting.
But the age at which animals may be used in breeding depends somewhat upon the individuality of the same, as, for instance, on the development and vigor, hence no cast iron rules can be framed that will equally apply to every case. But there can be no question of the wisdom of not allowing males to run with females, as a rule, at the mating season, lest the energies of the latter shall be taxed to no purpose by excessive service. Heredity will influence the breeding qualities of animals favorably or otherwise according to the breeding qualities of the ancestry*
The assumption is no doubt correct that fecundity is quite as much a matter of inheritance as of form. This has been repeatedly demonstrated in the practice of breeding. When it is desirable, therefore, to increase the fecundity, much care should be taken to choose both males and females from families which have been free producers.
Free production is as dependent on heredity as on food supplies in the ordinary operations of the breeder. The proper selection of breeding stock will therefore have much influence upon the rate of increase in a flock or herd.
Heredity not only influences fecundity as such, but it may also be made to exercise a powerful influence on the season of breeding. Under normal conditions grade ewes of mixed breeding drop their lambs in the spring.
In experiments conducted by the author at the Minnesota University Experiment Station, the breeding habit has been so changed in the first generation of the female progeny, that a sizable percentage of them, when bred, dropped lambs in the autumn, which is to say, between the end of September and the close of the year. In a few instances females of the first cross dropped lambs in September.
But those lambs were not the first birth. Pure bred Dorset sires were used, and the change in ‘the time of breeding already noted was unquestionably due to inheritance from them, although it was influenced to some extent by the food given to the dams.
Relation Between Size in Animals and Fecundity. —There is a marked relation between the size of animals and fecundity throughout the animal kingdom. The smaller species breed more frequently, more numerously, and at an earlier age. Cattle breed but once a year and produce but one at birth. Swine breed twice a year and produce several at birth.
Belgian hares breed many times a year and produce several at a birth. This may be owing in part to the modifying influence of the nutritive functions, but it would seem to be owing more to the inherent original constitution bestowed upon the distinct species.
While, as has been shown, fecundity may be influenced favorably in several ways, there is a limit to the possibilities of such influence. The cow could never be made to produce as the sow does, nor the ewe as the female Belgian hare.
Freemartins Usually Ban-en.—When a male and a female are produced at one birth, the barrenness of one has only been observed in the progeny of bovines. The female is barren. Such females are called “freemartins.”
It is only among bovines that this peculiarity occurs, and it is confined to instances in which one of the pair is a female and the other a male. The male would seem as able to beget as males ordinarily are. In rare instances the females also breed.
The primary reasons for this peculiarity are as yet unexplained. The internal generative organs of the female partake somewhat of the nature of those of the male. This explains the immediate cause of the barrenness, but no light is forthcoming as to the cause of such inheritance.
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