Katie Scotter, VetMB BA MRCVS
How many ewes do you cull each year? What should your targets be? Does any of this matter?
You might think that a barren ewe is no use to a sheep farmer, and only worth whatever her cull value is. But there is lots of information that we can take from cull ewes with only a few tests to maximise health and productivity of the flock the next season.
Flock performance targets are <15% cull, with <2% barren and <2% abortions in the flock. Assessment of reasons for culling highlights areas for intervention if too many are culled for a certain reason. Usually, there will be an even spread between animals culled for prolapse, caesarean, bad lambing, broken mouth, lameness, mastitis, poor udder conformation, barren and age.
Scanning enables you to pick out your barren animals earlier, which allows you to both sell them early to reduce feed costs around lambing and also to act on any infectious disease information earlier and before outbreaks occur. At scanning we would aim for <2% barren across all flock types. If your empty percentage is more than this, it certainly warrants investigation.
A simple blood test (lab fees are often funded) on 6-8 barren ewes allows us to monitor exposure to Enzootic Abortion and Toxoplasmosis in the flock. These are the two most common infectious causes of abortion in UK sheep flocks and both can be controlled by vaccination. If you do not scan, you can pick 6-8 ewes at the end of the lambing period that have either aborted or are barren and do the same test. This is a cheap, convenient way to monitor for these diseases in unvaccinated flocks, and to guide vaccination should it be required.
There are other reasons why a ewe may not get in lamb including poor nutrition, poor body condition, ram infertility, poor ram:ewe ratios, seasonality, lameness, parasites and other infectious diseases causing wasting/loss in body condition. It is good practice to investigate all of these factors by both physically examining the group, reviewing the numbers of ewes put to the ram, reviewing the ration and lameness control, and taking samples for diagnostic tests.
Cull ewes are usually the ewes that are struggling most in the flock, and any flock based problems are likely to be present in these animals. Examining this group helps to target our investigation into flock diseases by testing a small number of animals. A pooled faecal sample taken from the group can be examined for worm and liver fluke burdens to assess parasite control. Blood samples can be taken to test for Maedi Visna (MV), Johnes and Caseous Lymphadenitis (CLA) which all cause wasting. These are chronic diseases that often show very mild clinical signs until it is a flock wide problem and very difficult to tackle. There is no treatment or vaccination available for MV or CLA, and often we must cull these diseases out the flock, which is very costly.
Annual screening of barren and cull animals is a very simple, cost effective disease control measure that all sheep farmers can utilise. Be proactive and involve your vet to identify diseases before they become a problem, and to discuss where improvements can be made for next year. Next time you scan barreners, or round up your cull ewes to sell consider what they could be telling you about hidden disease in your flock.