- Managerial aspects affect reproduction in woolled sheep
|Last update: April 3, 2012 08:51:19 AM|
Managerial aspects affect reproduction in woolled sheep
Although it is certainly unnecessary to emphasize the importance of a high rate of reproduction in South African woolled-sheep flocks, surveys indicate considerable loom for improvement. At present only 65% of the country's available breeding stock produce lambs, which is aggravated by the death of 15-20% of lambs between birth and weaning. Bearing in mind that a minimum reproduction increase of some 60% is necessary to ensure progress in selection in a flock, the current situation, viewed at the breeder's angle, is alarming. In this respect it should also be remembered that farmers' capital investments in the purchase of good breeding animals are relatively high – which is a very sound policy - but owing to low percentage in reproduction they cannot turn to full account the genetic potential of these animals and in addition the return in their investment, in the form of flock improvement, is low as well in consequence. It must also be pointed out that these losses in regard to genetic improvement are setbacks, which can never really be undone.
Apart from the above, a high reproduction percentage naturally presents the farmer with immediate financial advantages. This feature is clearly reflected in data from mail-in records, namely, that precisely those farmers with the best reproduction percentages in their flocks are the very ones with the highest income per S.S.U.
Next the question arises whether there is something wrong in the reproductive potential of the woolled sheep and what can be done about it. However, it can be said at the outset that all available information shows there is no inadequacy in the fertility of woolled sheep. A single example from the Grootfontein Agricultural College Merino flock is proof enough. For the past five years this flock has averaged a reproduction percentage of 136,88% and an average of 122,36% of lambs per mated ewe has been weaned annually. Although these figures cannot be regarded as representative of the average extensive farming unit, they nevertheless do show there is ample room for improvement in the mean reproduction percentage of the country's woolled sheep. In this respect data from the mail-in records indicate that percentage-breeding increases of about 90% can be seen as realistic for such farming units.
In view of the foregoing, the problem of low breeding percentages in our woolled sheep must be largely ascribed to managerial aspects. The following are a few calling for careful consideration in a manager's programme:
1. MATING SEASON
Generally speaking there are two main mating seasons in South Africa, namely, during the autumn and in spring. Autumn pairing coincides with the peak of sexual activity in woolled sheep of the southern hemisphere. On the other hand, spring mating runs concurrently with the period when sexual vigour is at its lowest ebb. Without treating all the factors, which are at the root of higher or lower breeding percentages during the seasons above, it can be stated that a breeding percentage of 20% or more is normally prevalent in the case of mating in autumn. Although pairing is obviously the better, the choice of that season is influenced by several other factors. Of these the condition of our natural grazing is surely the most important. In the Karoo regions natural grazing is generally at its best in autumn. That season is preferred by farmers for the ewes to lamb (i.e. a spring mating) so that the lactating ewe and her lamb can profit by these favourable conditions. By contrast, it is often necessary to give supplementary feeding to the ewes which lamb in spring considering that natural grazing is relatively unfavourable just then. Apart from this important period in the cycle of reproduction, the following must also be borne in mind:
(i) Spring pairing occurs when natural grazing is relatively poor, which, besides the instinctively low level of sexual activity, represses it even further and shows resultantly poor conception figures. This also accounts for the markedly low breeding percentage, which follow an unfavourable spring season.
(ii) During the critical teeth shedding stage of young animals the lambs of spring-mated ewes also find themselves influenced disadvantageously at a comparatively bad time of the year (late winter and spring).
(iii) The first mating of the two-tooth ewes occurs immediately after this difficult period (in the case of a spring-pairing season). In addition it is during the time of inherently low sexual activity, the result being that breeding percentages are exceptionally poor, usually in maiden spring mated ewes.
Therefore in respect of the foregoing stages autumn pairing has the advantage of relatively good feeding conditions while supplementary feeding would most probably be needed in the practice of spring mating.
What has been said makes it clear that the choice between spring and autumn mating is influenced by a number of factors. The decision requires careful thought. Besides other managerial aspects the following guidelines are the most relevant:
(i) the respective feeding requirements of growing and breeding stock, especially at these stages of the reproductive cycle when needs are keener, such as the mating season, the last third of pregnancy and lactation:
(ii) the seasonal variations in natural grazing with a view to making higher feeding needs of animals coincide with periods of greater natural-grazing production;
(iii) the current prices of supplementary feeds in order to augment natural grazing when it is inadequate to the requirements of the stock;
(iv) the ruling prices of products (wool and mutton) and the proportionate return for wool relative to the figures for mutton, the latter being important in this respect that a better breeding percentage has even more importance in the framework of income/S.S.U. when mutton prices are relatively high compared with what wool can fetch.
Another method at the farmer's disposal to avoid the contradictions between the two main pairing seasons is to make use of both. This way out also has its problems, however. Nevertheless it will largely eliminate the heavy disadvantage of low breeding percentages connected with spring mating. Then there is the additional advantage of better use of rams since the same rams go into action in both mating seasons. However, management of the flock is complicated by the presence of two animal age groups within a single year. The worst problem, however, is the fact that a shift to the natural pairing period takes place and this gives rise to fewer and fewer animals being available for mating during spring.
In a special industry like that of the woolled sheep a good recording system, which permits efficient selection of breeding animals, is absolutely essential. When the part played by reproduction in successful selection for any characteristic is taken into account, the inclusion of the property, namely, fertility, goes without saying. In this respect the golden rule lays down that breeding animals, which have skipped two mating seasons, must be removed from the flock. This practice will also contribute to the elimination of "passengers" from a breeding flock, which will lead to higher efficiency. A system of this kind can, however, is applied only where a relatively high breeding percentage is obtained. Failing that achievement, the breeding flock will gradually diminish - a problem often associated with spring mating.
On the other hand the progeny of ewes with twins must be preserved in the flock as far as possible as genetic progress in regard to fertility is made to speed up better by selecting for twins than by merely getting rid of non-reproducers. With regard to this aspect the maiden ewe that produces twins at her first lambing is potentially among the most fertile of the animals: her progeny especially should be preserved (naturally excluding culling faults).
As a matter of interest it is worth recording that Australian researchers have established a comparatively close relationship between the LH level (a hormone) in 30-day-old lambs and the breeding percentage of their respective flocks. For this reason there is a possibility that we may yet have in future a direct criterion of selection for fertility.
3. MATING TIME
The mating season can be regarded as the beginning of the reproduction cycle; it deserves special attention with a view to achieving the best possible rate of conception. In extensive conditions it is desirable to transfer the ewes being mated to good grazing particularly if the pairing does not take place at the peak of the breeding season. Consideration must also be given to the fact that the rams, which are "hard at it" now, depend on the same grazing as the ewes. In consequence relatively weak pastures could limit the rams seriously in the performance of their duty.
The mating group should preferably not be larger than 200-300 ewes considering that the use of such group often leads to an uneven distribution of rams among the ewes; some ewes then miss being served by the rams. Likewise the mating camp must not be too large, must consist of reasonably even veld and should preferably have a few shady places and/or watering points. These would be a help in the regular gathering and mingling of separate groups in the camp. Should there be only large camps available, it is desirable to gather the flock together frequently to ensure the mutual association and intermingling of breeding animals.
Because maiden ewes cannot compete with their older rivals for the ram's attention and are often dominated by them, there is good reason to have them paired on their own and separate from the major pairing lot. For this purpose the young rams can be mated with the maiden ewes since the ratio of young rams acquired by purchase is usually proportionate to the number of maiden ewes introduced into the breeding flock. What is more, this is a way of stopping the fights between old and young rams and cutting out the losses, which occur. The superstition that old rams should be paired with maiden ewes and vice versa so that they may share in one another's experience has fortunately never been proved true. In fact, all available information indicates that the youngsters without experience manage just as well.
Particularly in the extensive areas of our country it seems that the alternating introduction of rams to the ewes has many advantages. It must be remembered that during the mating season the ram often covers long distances in pursuit of the ewes; consequently his full programme of "work" often prevents him from eating enough. A loss of strength intervenes and the efficient discharge of his "duty" suffers. The practice of dividing the rams into two groups and exchanging them every two weeks ensures that the rams with the ewes remain comparatively "fresh"; those which have been relieved of their job are then treated to good feeding (especially energy supplements) so that their strength can be renewed for the next "instalment of duty". However, during the last two weeks of the pairing all the rams may be left with the ewes.
Regarding spring mating, it is particularly important to note that because of the stimulus of the ram's presence most ewes start coming on heat only two weeks after the rams have been introduced. To save the strength of the working rams it is advisable to put teaser rams to the ewes during this period (i.e. the two weeks preceding the mating period).
In conclusion it must be stressed that every farmer and his farm are a unit, an entity; success in attaining an increased tempo of reproduction will depend on his ability and his initiative in applying some of the foregoing managerial aspects in his own specific conditions.
Merino Breeders Journal 40 (3)