Selecting replacement ewe lambs – Keep the best and sell the rest

A key factor affecting the long-term success of a flock is maintaining and improving the productive ability of the breeding ewes. This is achieved by selecting suitable replacements.

Some flock owners still purchase replacements accepting the associated risks in relation to disease status and productive potential. However, many flock owners now concentrate solely on selecting replacements from within the flock using their knowledge of the disease status and estimated productive potential of the lambs.

When selecting replacements you should aim to improve some or all of the following traits of the breeding flock.

Maternal ability – the number of lambs sold per ewe has the greatest affect on profitability. Replacements need to have the ability to produce and more importantly rear two lambs per year at maturity. Ewes, which have a good mothering ability and require minimum assistance at lambing will rear more lambs with reduced labour requirements

Although the heritability of multiple births is low this should not be ignored. Continually selecting twin born lambs will lead to increased lambing percentages.

Growth rate – lambs with higher growth rates are ready for weaning first and meet the target weight and carcase specification faster. Although growth rate has an average level of heritability, selecting these faster growing lambs as replacements, over a period of years, will lead to the production of lambs finishing faster and achieving a higher price. This has been particularly important over recent years where lamb prices reduced significantly over the summer period. Quite often it is the later smaller ewe lambs that are kept for replacements

The growth rate of lambs to weaning is also a good indicator of the milking and mothering ability of the ewe. Selecting the twin lambs heaviest at weaning as replacements should increase the future mothering ability and milkiness of ewes.

Carcass quality – this is not as crucial as the previous two, as the effect of the ram used on these replacements can significantly increase carcass quality of lamb produced. Carcass quality has a high level of heritability.

The key to replacement selection is to identify those twin lambs, which have the highest growth rates and bred from ewes, which required the least input to achieve this. The productivity of a breeding flock can only be improved by retaining rather than selling the earliest finished and best performing lambs.

It has often been said that a short pen is much more useful than a long memory. In sheep flocks where large numbers are often involved this is definitely the case and record keeping must play an important role.

AFBI (Agri-food and Biosciences Instititute – formerly ARINI, Hillsborough) have developed a management recording system for sheep flocks. Amongst many uses this system aims to identify superior ewes from which flock replacements should be retained.

The recording system is based around three simple recording booklets, a lambing book, a lamb weight recording book and a ewe checkbook. A range of information is recorded such as lambing difficulty score, requirement for assistance, mothering ability etc. The information from these booklets can be used to rank the performance of ewes in the flock. This system has the ability to identify ewe lambs suitable for breeding as replacements and most suitable ewes from which to breed replacements.

Traditionally replacements have been kept based on their own performance and that of their dam. However the adoption of performance recording by many pedigree sheep flocks means that rams can now also be selected based on their suitability to breed replacements. The generation of Estimated Breeding Values (EBV’s) for maternal, growth and carcass traits means that rams can now be selected for their ability to breed replacements.

Key points