Twinning in Merino sheep is a source of controversy in the Australian Sheep and Wool industry. Some wool producers prefer twins, many see twins as a nuisance and some actively dislike them. However, it is estimated that one quarter of all Merinos producing wool in NSW were born as twins. Wool producers seeking a long-term future in the wool industry can ignore the implications of twinning at their own risk.

The issue of twining in Merinos is that twins exist. This is only a complication depending on whether this fact is ignored or addressed.

Where the simple but important management needs of twins are not provided, twin bearing ewes produce lesser quantities of wool, tender wool and their progeny invariably are smaller in body size, higher in fibre diameter and lower in fleece weight.

Many wool producers say "I’d rather have one good single lamb". This attitude is understandable but irrelevant. The complications associated with twins will never, as many producers hope, "simply go away".

The better the nutritional management of the ewes, the more likely they are to have twins. Twinning rate is lowly heritable but will vary from year to year, in a flock, depending on the weight and fat score of the ewes at joining. Where ewes which have twins in year 1 are correctly managed, over 60 percent of them will have twins again in the following year. The comparable figure where twin-bearing ewes are not correctly manager is 30 percent.

Many wool producers would like to mark 90 to 100% of lambs. For this to happen there must be 20 to 30 percent of twin-bearing ewes in the flock. Twinning rates among spring lambing flocks of Merino ewes in Eastern Australia are 27% (range 2% to 51%). Table 1 shows the significance of twinning rate on a sheep breeding enterprise.
 

This example shows that many lambs, 41% (39/95) have been born as twins. Lambs born as twins but reared as singles still lag behind those born and reared as singles.

It is not surprising that many of the twin-born weaners are poorly grown under current management systems. This situation has proven to be one of the most easily eliminated by twin scanning and adjusting management practices.

Most woolgrowers have no idea of the numbers of twin-born hogget's going into the adult flock.
 

The take home message

Producers who twin scan their ewes; do so because the twins are there, not because they necessarily like them. And they do so because it is the means by which it is possible to produce greater quantities of better quality wool and lambs, more consistently and more profitably under conditions of high climatic variability.

The issue of twinning in Merinos is not about the advantages or disadvantages of twins – it is about the fact that twins exist and this is only a complication depending on whether this fact is addressed or ignored.