- Breeding soundness of Merino rams
|Last update: April 4, 2012 12:25:17 PM|
BREEDING SOUNDNESS OF MERINO RAMS
E. M. van Tonder
(Continued from October issue)
This term only describes the capability of a ram to reproduce, without considering whether he is a desired breeding animal. Fertility in the strict sense of the word actually means that a ram must be capable of producing semen containing sufficient viable sperm cells and must also be able to convey it to the ewe by the natural process of mating with resultant conception and production of progeny. This is a broad concept, subjected to variations of extremes from absolute sterility on one hand to maximum fertility on the other. In the natural process where one ram is mated to a number of ewes, a ram producing only one lamb from forty normal ewes should also be considered as fertile, although the degree of fertility will be considered much lower than that of a ram producing 38 lambs from 40 ewes. In this example it is of course accepted that the ewes are of maximum fertility and that all other factors opposed to maximum reproduction are eliminated.
Through the years a series of scientific tests were developed with the object of measuring the degree of fertility of rams as accurately as possible. These tests are collectively referred to as a fertility test where a complete fertility test was and is still considered to include an examination of the animal, his genital system and semen and to compare these findings with accepted normal standards. The genital system is examined to determine the absence or presence of abnormalities, while the semen is evaluated in respect of certain qualities, viz. colour, volume, density i.e. number of sperms per volume, percentage dead and live normal and abnormally formed sperm, mass and individual movement, etc. On the findings of these examinations a decision as regards the fertility of the animal is made. The aspect of the natural transportation of semen from the ram to the ewe has always been viewed as a matter of minor importance or an automatic process if the ram was free of any obvious anatomical or other physical defects.
Apart from and possibly to a certain extent also as result of the fact that an ordinary fertility test does not include the entire field of examinations, viz., the ram itself, the genital organs, semen production and quality, sex urge and mating, this test although it gives a very good Indication, cannot be considered as foolproof and a breeding test is the only true test for fertility.
The fact remains however that a ram suffering from certain abnormalities of the genital system, could still produce a reasonable or even a fairly normal semen picture and can therefore not be regarded as infertile. There are also other shortcomings as regards the method of collection of semen specimens, which make it impossible for a ram to be regarded as infertile on one examination only.
As rams, despite the presence of infectious or other abnormalities, but according to their semen pictures can only be certified as fertile and with difficulty as infertile and as it is often proved in practice that such rams are still capable of reproducing (regardless of how frequently and successful) the tendency has developed, to regard a semen test in other words examination of semen only and especially the percentage live sperm, as a fertility test. It is then also regarded as the only test of importance and on which a decision can be made regardless of its numerous shortcomings.
Improved mating practices like hand mating and artificial insemination, where natural movements and service are limited or even excluded, have also aided in drawing attention from the physical and anatomical properties of the ram and his genital system and thus contributed towards adopting or considering a semen instead of a fertility test as sufficient.
It must however, be stressed that the semen test is not condemned and that it is of considerable value, especially if it is carried out as part of a complete fertility test and perspectively viewed and interpreted. A complete fertility test should include general clinical examination, a specific examination of the genital system; complete semen examination (collection, evaluation and tests for specific infections) and a mating test i.e. determination of sex urge and mating ability. The mating test is usually, due to unavailability of ewes on heat, not practically possible and thus the clinical, genital system and semen examination must be considered as a complete fertility examination. The breeding test i.e. breeding with a number of ewes, is not taken into consideration as it will seldom be carried out as a result of its duration and practical impossibility.
BREEDING SOUNDNESS AND FERTILITY
With reference to the earlier definition of a breeding sound ram and especially the last part of it, viz. that it is a ram having a well formed, developed and functioning genital system, and which is also capable of reproducing, it will then be evident that fertility as defined previously is included here, on certain conditions.
Where fertility in the true sense of the word infers that a ram must produce sufficient viable sperm to induce offspring by natural mating, it is strictly qualified in the concept of breeding soundness, viz., the genital organs must function normally i.e. must, according to the average or accepted standards for normal rams, produce a normal quantity of normal semen, and the ram must also be capable of reproducing successfully in the natural way. In addition it is also stipulated that the genital organs must be well-formed and developed in order to complete the concept of breeding soundness.
The complete fertility test as mentioned previously boils down to a series of tests and examinations aimed at the determination of breeding soundness, as accurately as possible.
As a result of the tendency to regard a semen test as final and conclusive and to ignore all those physical properties, which are so tremendously important in breeding and reproduction, an alarming amount of confusion was created defeating the aims and object of breeding to a certain extent. The fact remains that all interpretations and decisions were centralised around the semen picture and certainly not around the ram as a breeding animal with due allowance for the object of breeding.
This was a dangerous turn of events as hereditary and contagious conditions of the genital organs in rams: were overlooked provided that these animals were capable of reproducing.
In order to eliminate this tendency and to maintain a uniform attitude and standards, the term breeding soundness was introduced and applied to the reproductive aspect of breeding.
This concept comprises no more and no less than a complete fertility examination, with the proviso that apart from any other culling faults, a ram suffering from abnormalities of the genital system would not be considered as breeding sound, whatever level of fertility he appears to have on the semen test.
OFFICIAL MERINO SALES
In view of the fact that these sales are held under the auspices of the Merino Breeders' Association and that this organisation also fosters the interests and improvement of the breed, certain minimum standards with regard to these sales were formulated. Those standards rule inter alia, that only breeding sound rams will be offered at these sales and this includes breeding soundness as regards reproductive properties.
As it is impossible at this stage to carry out complete fertility examinations, the abovementioned association adopted a decision that all rams offered at the official sales should also be subjected to a clinical examination of the genital organs and that these rams shall be judged sound or unsound on this examination only.
Although such an examination can be regarded as insufficient because subclinically infected and less fertile and infertile rams can be offered and sold, it still offers definite advantages and should be considered as a step in the right direction.
In the first instance is it obviously far better than no examination at all and does serve the purpose of reducing rams with infectious or other abnormalities to a smaller group of subclinically affected rams.
Secondly it serves the object of protecting the buyer directly and the breeder indirectly. It must be borne in mind that the buyer purchases at the highest bid and is surely entitled to a ram with two normal testicles and a normal genital system. If a buyer immediately, after a sale, should discover that he purchased a ram with one or another abnormality or breeding unsoundness, it is to be expected that he would be disappointed and dissatisfied, and there is always the possibility that the identity and good name of the breeder will be implicated.
Furthermore this is an important milestone that has been reached which will serve to make any further actions or the introduction of further examinations and tests so much easier. It must be remembered that these actions are not intended as disciplinary measures but are only carried out to advance the interests and improvement of the Merino industry.
It can finally be considered as being of importance in furthering the prestige of the industry, the sale and the Association.
Merino Breeders Journal 33 (1)