- Breeding plans for the Afrino stud breeder
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Breeding plans for the Afrino stud breeder
What is a breeding plan? It is the method used by a breeder to select certain animals (selection method) and the method that he uses to mate the selected animals (mating method). In a breeding programme, any selection method can be combined with any mating method. In this article, a few selection and mating methods will be discussed briefly.
A. Selection Method
A breeder's progress in his flock as far as certain traits are concerned is directly correlated with the selection method that he uses. In the case of the Afrino, growth rate and fertility are the two most important selection traits. The breeder's selection method should be aimed at improving these two traits. We assume that performance testing is applied and, therefore, that the identities of the sires and dams are known. It is also assumed that all the sheep used in the selection methods described hereunder conform to the minimum breed standards for conformation, wool and weaning index as set out in the breed standards.
1. Pre- and post-weaning growth rate
Growth rate is the mass differences at two given stages, the final mass being higher than the initial mass. The animals that grew the fastest are those with the biggest differences in their initial and final masses. In the case of the Afrino, two periods, namely (a) from birth to weaning and (b) from weaning to about 12 months, are important. To get the highest gradings, Afrinos must reach the desired carcass mass at the earliest possible age. Ewes should also grow rapidly to reach the desired mating mass as early as possible. Corrected weaning mass index will suffice for pre-weaning growth. Rams with indices higher than 100 and ewes with indices higher than 90 can be selected.
The selected rams and ewes are driven into separate camps and their masses noted from one to eight months later. The individuals with the biggest mass difference have grown the fastest. Preweaning growth is an indication of the dam's milk production as well as the inherent growth ability of the lamb. Post-weaning growth, which is highly hereditary, is an indication of the lamb's own growth ability. Because the latter is highly hereditary, the trait should have a genetic response.
2. Independent ram en ewe selection
According to De Lange (1981) the concept of the division of the genetic labour between the two sexes in animal breeding is becoming increasingly important. With this method, for example, rams are being selected for one or more traits. In the case of the Afrino, rams are selected for production traits, i.e. pre- and post-weaning growth, and the ewes are selected for fertility. Selection for fertility does not only imply selection for multiple births, but also Election for a long, reproductive lifetime with many lambs.
Using this selection method, the rams will be selected in the same way as in the case of selection for pre- and post-weaning growth (as discussed in A.1). However, the ewes are selected on the strength of their dams' reproduction performances. For this purpose the data in Table 1 is used.
When compiling the table, the facts that older ewes lamb with greater ease and are more inclined to have twins have been taken into consideration. Table 1 enables one to compare old and young ewes with one another. Each time that the ewe has been with the ram is taken as a lambing possibility. A young ewe that has produced a twin after her first mating is considerably better than a 5-year old ewe that has also produced a twin.
When selecting young ewes the indices of their dams, as reflected in Table 1, are allocated to them. Young ewes with the highest indices are selected.
Another method of selecting for fertility is by firstly allowing all young ewes to lamb. According to Olivier (1982, unpublished data) an analysis of the reproduction data of Merino ewes over a period of 18 years has indicated that ewes that had given birth to a single lamb at two-tooth produced an average of 0,94 lambs per year during their entire lifetimes. On the other hand, ewes that had not lambed at two-tooth had produced an average of 0,85 lambs per year during their entire reproductive lifetimes. Similar results have been found in other countries. For example, with Rambouillet, Dorset and Finnish Landrace crossings, Whiteman & Dyakuma (1981) have found that ewes that had produced 0, 1 or 2 lambs after the first mating produced an average of 1,33, 1,49 and 1,60 per year respectively during their reproductive lifetimes. It appears, therefore, that early-lambing ewes are more fertile and that they also lamb more regularly.
3. Ewe Productivity
In the extensive grazing areas - in fact, everywhere - it is desirable that the maintenance of the 'lamb factory' should be as low as possible. The maintenance requirements of ewes are directly related to their body masses. A ewe is more efficient if she weighs less and her lambs weigh more. Ewe productivity is no new concept and Nel (1980) has suggested it as a selection criterion in extensive areas. According to Erasmus (1981), a programme (at the S A Fleece Testing Centre) for the recording of ewe productivity, based on the total mass of wool and lambs produced, is presently being developed.
The criterion for ewe productivity that is suggested here is as follows:
Ewe productivity x
Corrected 100 days mass index is used so that a ewe which, for example, has two ewe lambs, can be compared with one that has two ram lambs. It is known that at weaning, ram lambs weigh more than ewe lambs. A considerable variation exists among ewes within the same flock as far as ewe productivity is concerned. For example, the ewe productivity of 191 ewes that have lambed during Sept/Oct 1982 at the Carnarvon Experimental Farm has varied between 0 - 709. Another example is the masses of lambs that have been weaned by ewes weighing 50 kg. The corrected 100 days mass indices of the lambs of these ewes varied from 81 to 220. This means that one ewe weighing 50 kg has produced a lamb with an index of 81. Another ewe, also weighing 50 kg, has produced two lambs with indices of 110 each. Obviously, the latter ewe is a better utiliser of the available feed.
Ewe productivity increases until the age of five years, and decreases thereafter up to the age of seven years (Olivier, 1982, unpublished). For this reason, ewe productivity must be compared within age groups. The average ewe productivity with in a given age group of ewes is established. All ewes with productivities higher than average are regarded as desirable. The minimum requirements above or below the average of the age group will, however, depend on the number of young ewes that must be selected. Preference canoe given to the progeny ewes that have been mated for the first time.
When selecting for ewe productivity, the following aspects are considered simultaneously: Pre-weaning mass gain, fertility and ewe efficiency. Rams and ewes can be selected on the strength of the ewe productive abilities of their dams. Rams can also be selected only for growth ability, while ewes are selected according to the ewe productive abilities of their dams.
B. Mating Methods
For successful fertilisation, regardless of the mating method applied, a number of factors are to be considered. Firstly, it is a fact that a larger percentage of ewes are in season during autumn than during spring. Secondly, before and during mating, ewes must gain mass. Thirdly, ewes must reach the desired mating mass (approximately 36 kg) and finally, fertile rams must be used.
1. Individual Mating
Because parentage identity is important, flock mating cannot be applied. Individual mating is practised by placing one ram into a camp with a number of ewes (approximately 30). All the lambs born to the ewes are the progeny of that particular ram. Preferably, the mating period should not exceed 42 days. One advantage of this method is that competition among rams is eliminated. A disadvantage of the method is that the ram used can lack adequate libido. Only a few, if any, ewes are served and the problem can only be identified much later, after the ewes have started to lamb. Good observation during the mating period can ensure an earlier awareness of this problem. Another disadvantage is that in the case of larger flocks, many camps are required.
When applying this method, an ewe that is in season is identified and a ram is allowed to serve her once or twice, after which the ewe is taken away and 14 days later she is again tested to determine whether she is on heat. Accurate recording is possible with this method.
All ewes are taken to a kraal daily and the ewes that are in season are identified, using a teaser ram. The mating period also lasts 42 days. After observing that a ewe has been served, she is placed into a separate camp together with all the mated ewes. The initial flock of ewes will, therefore, decrease daily while the mated ewes increase. All the ewes that have been served during the first week of the mating period are driven into a camp separately. The same applies to ewes that have been served during the second and third weeks. The ewes that have been served during the first week are placed with the unmated ewes after 14 days and are tested again. All ewes that have previously been served and are now on heat are mated once more but afterwards they are not tested again. The same procedure is followed with ewes that have been mated during the second and third weeks. According to results at the Carnarvon Experimental Farm, where approximately 800 ewes are mated annually according to this method, and those of the Grootfontein Agricultural College (Marx, 1982, personal communication), 80 - 99% of all the ewes have mated during the first 21 days of the mating period. An average of 6% - 10% of the mated ewes had to be mated again. An advantage of this method is that rams can be used very sparingly; because ewes are only mated to the rams once or twice, it has no negative effect on their semen. Rams with poor mating abilities or low libido are also easily identified. The possibilities of ewes being on heat but not mated are negligible. The disadvantages of this method include the facilities that must be available. The daily handling of the ewes can result in weight losses which adversely affect the ewes that are in season.
3. Artificial Insemination (A. I)
Most breeders are familiar with artificial insemination. As in the case of hand serving, ewes that are in season must be identified with teaser rams. The only difference between hand serving and A.I. is that in the latter case the breeder or manager - and not the ram - does the work. The management procedure with A.I. is the same as with hand serving. A.I. can also successfully be combined with oestrus synchronisation.
Before applying A.I. the breeder must become conversant with the procedure and preferably the inseminator must attend a course in A.I. Advantages of the method are: one ram can serve a large number of ewes, outstanding qualities can be in- bred easily and the semen of old, proven rams with certain injuries can still be used. Disadvantages include the facilities that must be available, the risks of in- breeding if one ram is used too much and the initial high cost of this method.
Suitable selection and mating methods have been discussed briefly. It must be stated that if the lambing percentage is below 100, little progress will be made with ewe selection as discussed in selection methods 2 and 3. In the event of it being necessary to increase numbers within a flock, it is obvious that ewe selection cannot be done. In the above two cases it will be desirable to use rams that are from twins.
De Lange, A.O. 1981. Patrone in die wolskaapbedryf - 20 jaar later. Verrigtinge van die Prof. F.X. Laubscher - herdenkingsimposium. 14 Nov. 1981. pp 136 - 141
Erasmus, G., 1981. Die ontwikkeling van prestasietoetsing van wolskape in Suid-Afrika. Verrigtinge van die Prof. F.X. Laubscher-herdenkingsimposium. 14 Nov. 1981. pp 184 - 200.
Nel, J.A., 1980. Ekstensiewe skaapproduksie. S. Afr. Tydskrif Veek. 10, 305 - 309.
Whiteman, J. V. & Dyakuma, J.M., 1980. Repeatability of ewe reproductive performance. Animal Science research report. Agricultural Experimental Station. Oklahoma State University No. MP 108, 14 - 17 (ABA 50, 3 207).
Afrino Maunal 2