Last update: April 12, 2012 08:02:01 AM E-mail Print

 

Selection in Merino Sheep Breeding

LL Roux

 

 

Heredity

HEREDITY incorporates the power of transmission of ancestral traits or characteristics, which may be inherited with surprising consistency. A Merino ram may inherit in detail the beautiful head and horns of his forefather; a particular strain or family of Merinos may be well known for wonderful body form and symmetry; while a certain stud may be famous for the superior quality of wool exhibited by its members.

However, the differences in body form and covering occurring in studs and flocks are well known to all breeders. When the combination of traits is modified or occurs in a new form, it is spoken of as a variation. Modifications are due to an irregularity of the breeding powers of the individual or individuals concerned. In studs in which systematic selection and breeding have been practised, the types of variation that may appear are not likely to be widely different to the established standard; however, where lack of discrimination in mating has existed, every conceivable variation seems to present itself and, consequently; the chances of obtaining a desirable combination of characters are considerably reduced.

The findings of scientific study definitely indicate that the inheritance of traits or characters is subject to principles or laws. While the general laws of heredity have contributed greatly towards a better understanding for the principles of animal breeding, the study of the expression and interaction of genetic factors giving rise to the characters of the new individual is without doubt a separate field of investigation in different species and sub-species. Thus, the inheritance of horns differs in cattle and sheep; in the Merino, the white fleece is dominant to the so-called black fleece, yet in the Karakul, black is the dominant fleece colour; and lastly, the combination of physical wool properties in the Merino fleece are peculiar to that breed.

 

Environment

The complexity of the problem is yet further increased by the influence upon the expression of characters of environmental factors, chief of which fall under the headings, climate, soil and feed.

Hereditary characters may be accentuated or inhibited in their expression by favourable or adverse environmental conditions respectively. Hence, the exact importance of either breeding or environment cannot be determined unless one or other is controlled or kept constant. It is conceded that wools tend to become dry and harsh when sheep are run on excessively limy soils, and that under-feeding or mal-nutrition results in starved, irregularly crimped, "tender" fibres or "breaks" in wool, but the more delicate effects of climate, soil, and feed upon the fleece of Merinos await investigation. There can be no doubt that a thorough knowledge of the effects of these agencies in different parts of the country would be valuable guides in selection.

It must be emphatically stated that the establishment and perpetuation of any character or group of characters depends upon rigid selection for the purity of that character or combination of characters, and that the results of the breeder can be best measured when the conditions under which the individuals are run are favourable for the perfect development or full expression of the powers of breeding.

 

The Problem and the Purpose

Selection involves far more than an almost random choosing of individuals for mating purposes. Without doubt, selection in the breeding of Merino sheep necessitates a study the depths of which breeders have not yet begun to fathom. In breeding, the complex problem is the regulation of creation with the final object of producing large numbers of individuals all of which, as closely as possible, approach the ideal sought.

The problem involves a careful consideration of body-form, symmetry, constitution, and wool covering.

Numerous character units contribute to each of these phases; the same character units are not always present in the same combination and degree of expression; moreover, the phases mentioned are to a large extent interrelated. Every part of the individual's body must harmonize, in order to attain perfect body-form and symmetry. The following may be mentioned as indicia of a good constitution, sound mouth, strong muzzle, deep and wide chest, good barrel, strong bone, etc. The important fleece properties are considered under extension, length, density, quality, substance, yoke content, colour, etc.

It has been stated that the phases, body-form, symmetry, constitution, and wool covering are interrelated. Thus, excellent body form and symmetry are in the majority of cases indicative of good constitution, while a sheep with a particularly weak constitution is not likely to grow valuable fleece. The presence of different degrees of expression of all the above give rise to the numerous combinations which, in practice, make the establishment of uniformity in Merino flocks and studs an exceedingly difficult task.

 

Establishing an Ideal

What is the ideal Merino which breeders so laboriously strive to create? Briefly, an individual of such superiority has every single unit character expressed in its highest degree of excellence and, in addition, is totally free of any body defect or fibre impurity. It is safe to say that the ideal is never reached; yet, it must be conceded that many excellent specimens of the Merino breed have been and are still being bred. The question often arises as to what may be termed an excellent specimen; diversity of opinion is widespread, and some conflicting ideas exist.

Selection demands a thorough conception of the details of each attribute which go to make up that recognized and desired goal. Furthermore, consistency of purpose is essential, while the distinction between disqualifications and faults or shortcomings should be rigid.

 

Systems of Breeding

The flock owner practises mass selection in its most extensive form; under his conditions, mating for improvement cannot possibly be more specific. However, the progress made in the flock will depend upon the selection, or the classing of both ewes and rams.

In stud breeding, selection tends to be rigid, and mating is under control. The high degree of excellence aimed at in studs is difficult to maintain, and certainly cannot be permanently established if the systems of selection and mating are not consistently uniform.

While "corrective mating" is recognized as a method or improvement, continuous subsequent selection is required in order to eliminate the defect or to establish a permanent change. Where a lack of density is in evidence, the shortcoming may be rectified by the use of sires that are equal in other respects yet denser than the ewes in covering. The same holds true for the improvement of size or any other single or compound character expression. The possibility of the occurrence of intermediate types is not entirely obviated, but it may be expected that the degrees of modifications will be less when the range of difference in the original types is small.

This broaches upon the subject of "extreme mating". While this type of mating is at times considered necessary by Merino breeders, its limitations should be recognized and its constant use discouraged. The question is, would it be more expedient to bring about improved density, where such is sadly lacking, by selection and judicious mating, rather than by the use of developed dense-woolled sires and subsequent selection, in order to obtain the desirable dense-woolled plain-bodied type? The answer appears to depend largely upon the material available, but it must be borne in mind that the individuals obtained by extreme mating cannot be considered genetically pure for the traits they exhibit. The constant mating of strong wool with fine wool Merinos appears to introduce complexities rather than to solve the problem of maintaining uniformity in flocks and studs.

The objects of improved systems of breeding are to establish and maintain desirable characteristics; in breeding and line breeding are used to accomplish these objects. In breeding is the mating of animals very closely related, such as brother and sister, father and daughter. In breeding must be accompanied by rigid selection for all characteristics, among which vigour and fertility are of paramount importance. Line breeding involves the mating between relatives, in order to concentrate on one line of descent the "blood" of one or a few individuals. It must be borne in mind that weaknesses or faults are as readily introduced and established as are desirable features, hence the importance of eliminating the former by selection.

The actual or true value of a ram can be assessed only by a study of (1) his pedigree; (2) the qualities he himself presents; and (3) the evidence of the results of his matings as reflected in his progeny. No great value can be assigned to a pedigree in which some famous individual occurs in a remote generation. The pedigree should gradually improve rather than contain a mixture of very good and very poor or unknown individuals. In general, it may be said that animals close up, or within two or three generations exert most influence upon the new individual.

In all breeding, homozygosity or purity of the genetic factors for the characters concerned, is of great importance. In practice, complete homozygosity is never accomplished, but breeders will readily proclaim the tremendous desirability and advantage of established uniformity within their studs.

 

Variations

Variation is the hope and despair of the breeder. Two types of variations should be recognized in Merino sheep breeding: the desirable and the undesirable.

The old types of Merinos were changed by selection which made use of the occurrence of variations. No doubt, present day types and strains are undergoing certain gradual changes. A Merino with an open face, a sufficiently dense fleece, and a good extension of fleece (belly and points) is no longer uncommon; breeders have obtained this combination through selection. Numerous unsolved problems with regard to many Merino characters are: If once an exceptionally rare desirable variation has occurred, can it be reproduced in the same way; does it occur in varying degrees; and what results will be obtained by mating the old and the new type or by mating the latter "inter se"? Such information can be obtained only when selection and breeding are consistent. Apply the above questions to a specific case, namely, that in which the "jowled condition" has established itself in an excellent stud. The condition occurs in varying degrees, while, in the instance quoted, the abnormal cases are those which are devoid of the undesirable lateral facial development. It may be contended that the jowl fold is an extension of a particular pattern of frontal development. If, in the same stud, individuals occur with a degree of frontal development sufficiently typical of that stud yet devoid of jowl folds, it would indicate that the latter are separable from the former, and that, consequently, the chances of eliminating the jowl fold by selection are assured.

At times, it is advantageous to attempt to create certain variations. The point arises, is it better to endeavour to cause such variations within a stud, strain, or type, rather than to cause their occurrence by an infusion from a foreign source? Generally, the former is the safer procedure, as an introduction may upset the otherwise desirable established combinations of characters.

Even in remarkably good studs, undesirable variations and reversions constantly occur. Here, consistency in selection is given its severest trial; breeders are prone to become too forgiving. The evils of excessive body development (wrinkles) and superfluous body folds are well known. Sufficient bulk of fleece can be obtained without resorting to such body development; moreover, the well-bred plain-bodied sheep with good bulk has the power of transmission of this quality, while there is great danger of increased development when selection does not eliminate this latter characteristic.

The subject of variations introduces the question of serious defects and disqualifications. Certain improvements may be brought about by corrective mating, but when defects have become disqualifications, culling is the only remedy. The operation of drafting and culling is often a painful task, but what can be more serious than the rapid and extensive introduction of bad hocks, kemp, "hair," etc., through the use of a sire who may exhibit, or carry in a latent form, one or more of these undesirable characteristics? In such instances, the attitude of the breeder should be unforgiving. Defects of a serious nature are usually more easily introduced than eliminated.

Large numbers are important at the present stage of our breeding knowledge of Merino sheep. As the purity of type becomes established through selection and breeding, more specific or careful attention may be paid to fewer individuals. It is definitely advocated that the inexperienced stud-breeder, working with a small heterozygous or mixed collection of sheep, should be discouraged. Rather be an owner of a good flock than a breeder of poor studs.

 

Selection in Flocks

The commercial flock-owner's task is by no means an easy one. His principles should be to select for (1) Vigorous, upstanding, good constitutioned sheep; (2) a type of wool in constant demand, suitable to local conditions, and yielding, the best financial return per capita: (a) good quality, and the best combination of length and density for its protection and (b) the maintenance of uniformity of fleece and clip; (3) elimination of weaknesses, and the total exclusion of undesirable features, such as bad hocks, "hair," kemp, watery wool, etc.

 

The Financial Aspect

The financial aspect plays far too important a role in selection to permit its omission from this discussion.

The step in the ladder of progress at which the Merino flock-owner and the stud-breeder start, will depend largely upon the extent of their ability to invest capital in the particular enterprise, and secondly, their ability to determine whether the price quoted is a fair value for the class of sheep offered for sale.

Assuming that the breeder is a good judge of Merino sheep and that he is consistent in his selection, the speed of progress in the initial stages of flock and stud improvement depends upon financial ability to purchase improved animals. The purchase of a high-priced ram for use on mediocre ewes would be equivalent to the investment of a large sum of money in a business of doubtful stability. The safer procedure is gradual improvement and subsequent heavier investments when the ewes have attained a higher and more dependable standard of excellence.

Advanced stud breeders not only depend upon their own studs for suitable stock, but they also have the opportunity of establishing themselves as sellers of high standard and reliable breeding ewes and rams.

 

Published

Farming in South Africa 4