- Breeding soundness of Merino rams
|Last update: April 4, 2012 02:49:16 PM|
BREEDING SOUNDNESS OF MERINO RAMS
E M. van Tonder
There are probably very few words as frequently used in the livestock industry than the word "breeding". This is indeed necessary as it forms the basis upon which each species, breed or strain is founded and where they originated. It is furthermore also the key to improvement and perpetuating the desired qualities of any breed or species.
Although this word is freely and often lightly used without full comprehension of its meaning or implications, it still remains of primary importance and application to all levels of any livestock, including the Merino industry. It is practised by the ram breeder for instance to improve the standard of his animals and to establish as many of the desired properties as possible in their progeny. The flock farmer on the other hand although not specifically adjusted to it favours similar intentions; namely the improvement of his stock through breeding and the utilization of rams purchased from a breeder. Consequently, each and everyone involved in this industry, under the vigilant eyes of the relative associations, takes a hand in improving the breed, furthering the interests of the industry and satisfying the demand for its particular products especially as regards quality.
By means of definition, the concept of breeding in animals and as such in the Merino as an established breed and strain, can be regarded as the successful mating of selected male and female animals, in order to improve the breed and to perpetuate the desired qualities in the progeny, with due consideration of specific circumstances.
On closer study of this definition we find that there are two expressions, namely "successful mating" and "selected male and female animals" requiring further attention. In the first mentioned case viz., "successful mating" the expression can be taken literally namely that from this particular association between the two sexes, offspring must be obtained, in other words lambs must be born. On a stud or flock basis i.e. where a number of animals are involved, mating should be followed by conception and pregnancy of the female animals and at the termination of this period, viable and healthy lambs must be born. In practice there is always the wish to achieve the ideal results where each and every ewe produces a lamb. At present there is also the propensity to select for multiple pregnancy in order to increase reproduction. As regards this particular aspect and in order to accomplish the abovementioned aim, it is a definite prerequisite that both rams and ewes should possess a high level of fertility and that all other factors opposed to successful mating be reduced to a minimum.
In order to possess a high level of, or maximum fertility, it is again an absolute prerequisite that each and every animal should have a well formed, developed and functioning genital system. In view of the fact that abnormalities of the genital system are usually incurable and often due to their hereditary tendency, not desirable to attempt treatment or to breed from such animals, we are therefore committed to selection as the only means to ensure that only animals with normal genitalia and breeding ability are used for breeding purposes. It is therefore necessary that normal genital systems should also be selected for not only to ensure a high level of fertility but also to prevent hereditary abnormalities to be transmitted to the progeny.
As far as the other expression is concerned namely "selected male and female animals", the meaning is equally clear in as much as it is meant to convey that animals intended for breeding purposes should be subjected to an inspection previously. This inspection is usually aimed at breeding standards i.e. the presence or absence of decided outstanding and poor properties. In order then to satisfy the requirements of our definition of breeding, it obviously follows that discrimination should; be made in favour of outstanding and against poor properties. The degree and strictness of selection will depend on the individual, the type of breeding, i.e. stud or flock, the standard of sheep and the particular aim and degree of improvement to be accomplished.
From the preceding statements it will be evident that selection forms the basis of the whole process of breeding. It is equally clear that selection should not only be based on type, conformation and wool properties but must also include other properties like fertility and especially the condition of the genital organs.
The ultimate aim of selection in this respect is then to sort out and use these animals that are deemed suitable for breeding purposes. In view of the fact that this subject covers an extensive field and in order to keep the, object of this article, we will henceforth only concentrate on Merino rams.
This term actually comprises the result of breeding selection as described previously and therefore includes the particular group of rams that we consider suitable fur breeding purposes. It actually describes those rams which the owner or prospective owner would like to breed from. The standard or level of breeding soundness will obviously vary from individual to individual but minimum standards and culling faults, as determined from time to time, are aimed to serve as a guide and to maintain a minimum level.
A ram which is breeding sound thus represents a ram that conforms to the minimum breed standards, is free of culling faults, possesses well-formed, developed and functioning genital organs and is capable of reproducing successfully under natural circumstances
In the first instance the reader is referred to an explanation of standards of excellence as well as the official list of culling faults of the Merino as adopted at the Annual General Meeting of the Merino Stud Breeders Association and published in the July issue of their journal.
Breeding soundness concerning the genital organs of Merino rams will now be dealt with in more detail.
It might sound unnecessary to mention that a ram without functional sexual organs is incapable of reproducing or that a varying degree of impairment of function will influence his reproductive ability to a similar extent or obviate the full exploitation of the breeding potential of such a ram. It might also sound unnecessary to state that abnormalities in the shape and structure as well as development of the genital organs exercise a direct influence on the functioning thereof. These basic facts, despite their immense importance, are however often neglected or ignored.
Although a normal genital system is a basic requirement for breeding and one of the most important deciding factors of breeding soundness it is absolutely inconceivable why this aspect has been so dreadfully neglected and ignored through all the years of Merino breeding and even still today. It is absolutely shocking, despite extensive campaigns of propaganda and publicity to have to find daily that rams are purchased or sold with advanced and easily discernable abnormalities of the genital organs and to be informed on top of it that it never occurred to either the breeder or buyer to pay attention to the genital system. In these cases a poor or no breeding performance of the ram is usually the first and only indication of this type of breeding unsoundness to the new owner.
In this respect the smaller abnormalities or those that are difficult to recognise can still be excused but advanced abnormalities like complete absence or decrease in size of one or both testicles and pronounced and chronic lesions of infectious infertility as experienced daily are indefensible. One shudders to think how often it really happens that these unsound rams are sold and used for breeding seeing they could still be fertile in a variable degree, are used for mating in a group and are replaced by breeders, depending on the degree of abnormality i.e. whether the new owner becomes aware of the existence of such a condition. These rams are seldom examined or offered for examination with the result that true figures are not available.
It will therefore appear as if this type of breeding soundness was and still is completely entrusted to the abundant provision of Nature. It is also probably due to Nature's provision that a more serious or even catastrophic condition has not yet occurred in the Merino industry.
A discussion of the more general abnormalities of the genital system of rams will now be endeavoured. It must be remembered that the presence or absence of these abnormalities and in isolated cases the degree of incidence will determine whether a rain is breeding-sound or not. The majority of these defects are permanent while a few conditions could be of a permanent, or temporary nature.
1. Hypoplasia and atrophy.
These are conditions of the testes, which occur frequently and with increasing incidence.
Both conditions describe a decrease in size of one or both testicles. In hypoplasia the decrease in size is due to the fact that the testicle did not develop to its full or normal size while in the case of atrophy development to normal size was completed but the testicle decreased in size afterwards.
The condition in both cases can occur in a variable degree in one or both testes. In both these conditions the affected testicle is flabby and inelastic on palpation but in atrophy it is often irregular, hardened and sometime calcified.
Atrophy is always of a permanent while hypoplasia although usually of a permanent could also be of a temporary nature. Temporary hypoplasia is also called “delayed development" as result of the fact that young rams at certain and also variable ages might have small and flabby testicles, especially when compared to normal rams of the same age group and in the same stud. while at a later stage they are fully developed. One or both testes can also be involved while the age at which complete development takes place, may vary from two-tooth to full-mouth.
Atrophy is usually caused by bumps, bruises or an acute inflammatory process of the testicle itself. Hypoplasia and delayed development are usually the result of an hereditary tendency or factor and strict inbreeding.
It is often very difficult to differentiate between hypoplasia and atrophy especially when hardening in the case of atrophy has not yet taken place. Where a lesser degree of hyoplasia of both testicles occurs, it is sometimes difficult to recognise the condition and flabbiness, inelasticity, size of the testicles for the particular age and a comparison with other rams in the same and also similar groups are therefore the only signs on which a decision can be made. Although there is a reasonable variation in the genital organs of rams, the Merino is known for the size of its testicles and are large and firm - elastic glands favoured for this particular breed. The fact that all rams in the same age group and stud show smaller testicles, must not unconditionally be accepted as normal, as it could most probably be the result of inbreeding over a long period and lack of selection in respect of the genital organs.
Temporary hypoplasia or delayed development can also not be differentiated from hypoplasia unless a ram is examined on consecutive occasions.
In the estimation of breeding soundness it is discriminated against both these conditions because they are responsible for a varying degree or even complete impairment of function of the sex glands resulting in the fertility and breeding ability of the ram being partly or completely suppressed. Hypoplasia is in addition to this also a hereditary problem.
Although it is impossible to determine its existence after complete development has taken place and it probably has no influence on fertility at this stage, rams that showed delayed development should not be regarded as breeding-sound and used for breeding purposes as they, usually without exception, constitute what can be considered sensitive rams. Sensitive rams can be described as those which, on every and sometimes slight changes and treatment of variable duration, will show partial or complete infertility. In view of the fact that this condition cannot be determined after normal development of the testes has taken place, it is impossible to prevent rams that showed delayed development being put up for sale.
On account of the fact that hypoplasia and delayed development are hereditary conditions, it must be borne in mind that they can also affect the female genital glands and that the consequences of utilization of such rams in a stud could therefore be transmitted to both sexes.
2. Epididymitis, Orchitis, Epididymo-orchitis
This group of conditions indicate inflammatory condition of the genital organs. Epididymitis describes an inflammatory process of the epididymis, orchitis a similar condition of the testes and epididymo-orchitis the condition where both these structures are involved.
These conditions are infectious, usually also contagious in nature and are caused by specific micro-organisms.
For a detailed discussion on these conditions, the reader is referred to an article, which appeared in the April 1969 issue of the Merino breeder's journal.
These conditions usually result in permanent damage of the genital organs due to the fact that chronic lesions and/ or atrophy is common sequelae and that complete healing is never effected.
We discriminate against these conditions on account of the fact that apart from the influence of fertility and breeding ability they are also infectious and contagious in nature.
This term is applied to varicose wins in the spermatic cord. It is usually situated above the testicle, in the spermatic cord and in the vicinity of the external opening of the inquinal canal. It is probably caused by bruising and stretching of the veins.
It usually starts off as a small swelling or thickening in the spermatic cord with an irregular surface. It gradually increases in size and can sometimes become even bigger than the testicle. The appearance on palpitation can be compared with a densely packed bunch of grapes just before the ripening stage. In the initial stages it does not affect the ram or its fertility but as it increases in size, it becomes more and more painful, until in the later stages, the animal moves with difficulty and a characteristic gait. The hind legs are kept apart and the hindquarters are lowered. During the later stages and due to the increase in size, it could interfere with the normal blood supply, either directly or due to pressure on the spermatic cord, with resultant atrophy of the testicles.
In this condition fertility and breeding ability are impaired due to pain, interference with the normal blood supply and inability or reluctance to serve. This condition is usually discriminated against because it progressively increases in size.
4. Abscesses on the scrotum
In this case reference will only be made to single isolated abscesses, occurring on the scrotum, not attached to the testes and usually situated Ion the division between the two sides of the scrotum.
These abscesses have, apart from pain and possibly pressure on the testes with resultant atrophy (depending on the size of the abscesses) no other or permanent effect on fertility or breeding ability. It can usually be drained or removed with relative ease and will on condition that no complications set in and no abscesses or indications thereof, occur elsewhere in the body, have no effect on breeding soundness.
While these abscesses are still present, they constitute and are regarded as abnormalities and will render the ram unsound for breeding at that particular stage. Depending on the nature, degree, distribution and effect on the genital system, the condition caused by these abscesses, can be regarded as a temporary abnormality.
These abscesses are usually caused by bacteria, which are introduced by tick bites, thorn-pricks and shearing wounds. The most common organisms involved are Corynebacterium ovis, Corynebacterium pyogenes and some streptococcal species.
5. Long (pendulous) scrotum
This is a congenital and probably also an hereditary condition, which has no direct influence on fertility or breeding ability. It can however induce lowered fertility or infertility and poor breeding performance, due to the fact that it is predisposed to injury and bruising.
This is a condition where degree of intensity will be considered as an abnormality and will therefore determine whether a ram is breeding-sound or not.
6. Other abnormalities
There are still quite a number of abnormalities influencing breeding soundness, which are sporadically encountered. Due to their occasional incidence some of these will only be mentioned here.
Amongst those which cause permanent breeding unsoundness, the following can be mentioned: Crooked (skew) penis, low-hanging (suspended) penis (where penis is not situated against but suspended in a loose skin fold, away from the belly as in certain cattle breeds), pronounced prolapse of the mucous membrane of the sheath, cryptorchidism, cleft scrotum, inquinal and scrotal hernia, etc.
In this particular group of abnormalities which are usually temporary but depending on the degree of intensity, duration and complications, could also be permanent in nature, the following are of importance: Scrotaldermatitis (inflammation of scrotal skin), inflammation of the sheath, urinary calculi, mange, etc.
Merino Breeders Journal 32 (4)