Fertility drug will have great effect on industry

Press, 30 September 1983, Page 26

Fertility drug will have great effect on industry

By

A. D. Ross,

Ministry of Agriculture and

Fisheries Animal Health Laboratory, Lincoln.

A new ■ fertility drug due to be released soon will have a profound effect on the sheep industry. The drug, scientifically named Polyandroalbumin, dramatically raises the number of lambs born. New Zealand trials have shown an average increase in lambing percentage of 25 per cent and up to 45 per cent has been recorded. Increases are in addition to those gained by mating ewes at heavier body weights and using flushing feeding techniques. The drug was developed by the C.5.1.R.0. in Australia. It acts by increasing the number of eggs shed from the ovaries of the ewe. When fertilised the eggs result in the birth of extra lambs. The number of ewes in a flock having multiple births is raised but the number of barren ewes will remain the same.

A two millilitre injection is given under the neck skin about seven to eight weeks before tupping. A second injection is given four weeks later. After the first year, only one annual dose is required. So far research indicates that there are no problems concerning the action of the drug on sheep. The effect only lasts for that mating season and is said not to affect the subsequent fertility of the ewe or her offspring.' Following a ruling by the

Animal Remedies Board, farmers will be able to buy the drug from veterinarians and stock and station agents some time before the end of the year. The cost has not yet been determined but will probably be about $1.50 per dose. A new product with such enormous potential will be an attractive proposition to many sheep farmers, but careful planning is needed to maximise financial returns and minimise costly mistakes. The rest of this article is devoted to describing some of the points farmers and their advisors should,consider before they use Polyandroalbumin. A thin, low bodyweight ewe is not a good candidate to become the mother of twins or triplets. It will be

tempting to try to raise the lambing percentage of the “tail” of the flock, i.e., those ewes with low bodyweights, by using this drug. Similarly, injecting two-tooth ewes may be considered. However, it should not be used to compensate for low bodyweights caused by poor nutritional management or disease. The best candidates are those well grown ewes capable of carrying and feeding twins and triplets. In some flocks well grown ewes that tend to bear single lambs can be identified and when nutrition has not been a limiting factor, these ewes may particularly benefit from the treatment. Fewer big single lambs would be borne with fewer dystocia problems. It may be desirable to avoid injecting ewes who naturally produce twins and triplets, unless triplets and quads are desired. In addition breed societies and stud breeders who select superior ewes on the basis of their natural fertility will have to carefully consider what they are doing before using the drug in their flocks. To select the most suitable animals for treatment farmers must know the bodyweights in previous lambing history of their ewes. Animals that were previously culled for barrenness should still be

culled as the drug will have no effect on their fertility. A decision will have to be made to either increase the total number of lambs born on a farm or keep the total number of lambs unchanged and reduce the ewe numbers. While over-wintering and growing flushing feed for fewer ewes may be attractive in some areas, the reduction in the ewe wool clip may make this option unattractive in others. Availability of feed for ewes and lambs may limit the number of ewes a farmer should inject. It will be important to achieve high ewe bodyweights for mating. Providing flushing feed can be regarded as an optional extra but should result in an additional increase in lambing percentage. In late pregnancy and from birth to weaning it is necessary to preferentially feed ewes bearing twins and triplets to avoid problems associated with pregnancy toxaemia, ' mis-mothering and poor milk production. Reliable machines for pregnancy diagnosis may become available in the near future and would allow these animals to be identified. For the farmer whose

flock will have increased numbers of twins, triplets and even quads there will need to be a significant change in management at lambing time. These lambs have lower bodyweights than single lambs and suffer from exposure more quickly. Providing good shelter is essential if high death rates are to be avoided. Even so, assistance in early feeding may be necessary to ensure maximum survival.

Mis-mothering is also more likely to occur in flocks where multiple births are common. Lambs are best not moved from birth site for the first few days of their lives and stresses such as dogs and motor bikes must be kept to a minimum.

In one set of trials in New Zealand the average recorded death rates in flocks from birth to weaning were 13 per cent for singles, 21 per cent twins, 33 per cent triplets and 50 per cent for quads. These figures will vary between farms and between years but indicate that an increased number of lambs born does not automatically result in an increased number of lambs weaned.

Obviously if the total

number of lambs born does not automatically result in an increase number of lambs weaned.

Obviously if the total number of lambs weaned is to be raised then the total amount of pasture available to lambs must also be increased. However, even in flocks where the total number of lambs remains the same consideration must be given to maximising their growth rate. This will be particularly important where farmers are attempting to produce export quality lambs. If growth rates are not maximised, the lower birth weights of twins and triplets will result in lower weaning weights. These in turn may alter the drafting patterns and returns to the farmer for carcase meat.

There are no hard and fast rules which can be applied to the use of this drug on all sheep farms in New Zealand. But careful planning must be carried out to maximise the financial benefits.

It is necessary to know whether the feed supply will support the extra production. While an increased lambing percentage can be confidently predicted, it cannot be assumed that, without good management, this will automatically be translated into increased weaning percentages.