Isolating ewe wastage

Identifying exact ewe wastage percentages and their cause remains difficult, vet Rachael Fouhy writes.

Tail-end ewes are a common issue on many farms and can be a frustrating problem. As a general rule tail-end ewes refers to those in body condition score 2 or less who fail to improve.

Many farms have a standard management procedure whereby tail-end ewes are drafted off at set times of the year and preferentially fed; some improve but some don’t. Tail-end ewes that don’t improve represent a significant expense in our sheep production systems as they are not reaching their full potential.

Ewe wastage issues can result in farms needing to keep more replacements and/or having to keep poorer-quality ewes for another season. Very little work has been done into the exact causes of tail-end ewes and there are wide variations in the wastage numbers on different properties. The extent of our farming systems and the lack of individual sheep ID makes identifying the exact wastage percentages and the exact causes difficult.

Based on data from Massey (Ridler et al 2022, Flay et al 2021) we know reproductive outcomes are a key cause of wastage. We also know dental issues are also a common cause of culling.

It is important to understand what causes issues on individual farms so we can manage these better and look for opportunities to minimise them. There will also be a time in the future where we are required to have more in-depth information regarding wastage as part of onfarm audits, market access and animal welfare requirements.

Common causes of poor ewes on farms in my district are most often diagnosed by an onfarm visit, some bloods and faecal samples and some selective post mortems. Checking your kill sheets and looking at this data can also provide useful information and trends.

Things I look for when investigating ill-thrift/tail-end ewes include:

The age structure

Is there one group that is more adversely affected than another group? E.g. are the majority of ewes five years or older or is this a widespread flock problem?

Recent drenching history

What is the drench status of this property and have the ewes been drenched recently? We know that in adult ewes only about 10% of skinny ewes are light due to a parasite problem – this applies to most farms but there are exceptions. Make sure you do some FECs on light ewes to get an understanding of potential parasite burdens.

Trace element status

Selenium (Se) is the main trace element issue I see. Se is very important for growth and immunity. Low levels can result in decreased growth rates and also a weakened immune system. While in some situations B12/Cobalt can be an issue, this is much more likely to be a lamb-related issue, especially during autumn. Regular monitoring via livers is a good time to measure trace element status.

Facial eczema incidence and tolerance

While northern areas of the country have lived with eczema for generations, this is becoming more of a challenge in the lower North Island where it previously hasn’t been a common issue.

We know eczema is commonly referred to as an “iceberg disease” and the number of clinical cases we see is far fewer than the number of subclinical cases there are, therefore do not use clinical cases to estimate the impact of this disease.

To assess if eczema is a risk for you, monitor spore counts in the district, get some testing on your own farm, consider blood testing ewes and utilise post mortem information. Look to future-proof your business by investing in FE tolerant genetics.

Teeth

Recent work at Massey University indicates 80% of sheep farmers mouth sheep and cull ewes on teeth. We all know low mouths or gappy teeth make it harder for sheep to eat enough food and these ewes are prone to being lighter. Molars are more difficult to assess but are equally important in terms of a sheep’s ability to digest food.

Post mortem

This is a cheap and easy way to identify causes of ill thrift. The key is to do more than two sheep to ensure you get a realistic idea of the causes of ill thrift and are not being led astray by one sheep. Common issues we identify at post mortem include pneumonia, johnes, intestinal cancer, chronic parasite damage, liver fluke and intestinal carcinoma.

Liver fluke is different from other parasites in that animals do not develop immunity to it. It is also not picked up on a standard FEC. Liver fluke requires an intermediate host, a snail, in its lifecycle and therefore is not on every farm. It tends to be in certain areas, more likely where sheep are drinking from swamp areas. Liver fluke can be easily diagnosed on post mortem where the flukes appear like flat black slugs about the size of a thumb nail. It can also be diagnosed in blood samples.