Last update: April 5, 2012 07:31:50 AM E-mail Print





UNDER extensive farming conditions, flock mating is the method applied most generally by farmers today. With this system, a group of rams is usually mated with a flock of ewes in large camps. The degree of success achieved cannot be determined until a fairly advanced stage of pregnancy among the ewes, by which time it is impossible to prevent disappointing results.

It is a known fact that rams can play an important part in the flock by determining the size of the lamb crop. It is known that with flock or group mating the rams compete against each other to cover the ewes on heat which delays or even prevents their being covered. Some rams will nevertheless eventually succeed in covering the ewes in competition with other rams.



An order of precedence then becomes established, in which the rams may be classified from strong or "dominant" to weak or "inferior ." The most dominant ram will mate with the greatest number of ewes - but will not necessarily impregnate them - and will also exercise an important influence on the genetic progress within the flock. If one of these dominant rams is of a poor genetic composition, this may have far-reaching consequences on the genetic improvement of the flock.

When using this mating, system, it is impossible to identify the sexually adroit rams - those capable of serving a maximum number of ewes in a minimum time. If rams with a weak sexual urge (libido) and poor sexual adroitness are unknowingly used in flock mating, it may reduce the lambing percentage considerably. In order to avoid this, the farmer is compelled to use a relatively high percentage of rams to ensure a satisfactory lamb crop, This increases costs considerably.

Certain environmental factors such as camp size also determine to some extent the efficient utilisation of rams. These are factors the farmer must remember in order to reduce the production cost of lambs. The use of small camps during the mating season, for instance, may assist in obtaining mote efficient exploitation of the ram potential



By permitting two rams to compete for one ewe in oestrus, dominant and weak rams were classified into various groups according to dominance. Thereafter the influence of dominant and weak rams on the lamb percentage was investigated by putting the rams separately to non-pregnant ewes in camps of two different sizes (50 and 230 morgen).

In each camp one Merino ram was put to 130 Merino ewes. Each ram was provided with a marking harness, making it an easy matter to identify ewes, which had been marked and probably covered.



A higher number of ewes were marked by the dominant rams than by the inferior ones, and most of them eventually produced lambs (Fig. 1). A striking feature of the experiment was the rapid decline in the number of ewes marked weekly by the weak rams in both the large and the small camps. This emphasises the fact that weak rams Showed only slight interest in the oestrus ewes. As the mating season progresses, such rams gradually lose interest in the ewes, with the result that fewer ewes are served.

The number of ewes marked weekly by the dominant rams, on the other hand, remained approximately constant in both the large and the small camps (Fig. 1). This indicates that these rams revealed a good sexual urge throughout the entire mating season. The practical implications of this on increased lambing percentage and curtailment of the lambing season are obvious.



Judging by the number of ewes, which were covered during the four successive weeks and ultimately, lambed, more ewes were covered unsuccessfully during the first week than in the following weeks. This phenomenon is particularly noticeable in the case of the weak rams.

No significant influence of camp size on the lambing percentage was observed, but slightly more ewes were covered by dominant and weak rams in the small camps than, in the large ones. Similar trends were found in respect of the number of ewes, which produced lambs.

It was also found, however, that although some rams show good sexual adroitness and a strong sexual urge, some ewes in oestrus are served only with great difficulty. Such ewes in the breeding flock may therefore also contribute considerably to the unsatisfactory lambing percentage, which usually occurs under extensive conditions. If such ewes can be recognised - which is a very difficult matter in practice – and they are removed from the breeding flock, this may also raise the lambing percentage. The influence of the ewe in flock mating, however, is less important than that of the ram.

It is therefore clear that both rams and ewes play an important role in mating behaviour under flock conditions. If dominant rams, with good sexual adroitness and of a high genetic quality, are mated in small camps with ewes, which are easily served, this may increase the lambing percentage considerably. It can also speed up genetic progress within the flock and reduce the duration of both the mating season and the lambing season, thus facilitating general flock management.



Farming in South Africa 42 (6)