Culling ewes

Compiled by Jane Court, Agriculture Victoria

This may be an opportune year to cull less productive ewes from your flocks.

Strategic culling of lower production animals will reduce feed requirements while maintaining production into next year. There has recently been some good work done on the impact of poor udders on future lamb survival/performance. There is also the need to have the most appropriate age structure of your flock balancing the genetic gain from bringing in young ewes versus getting the most productive years from older ewes.

Wet and dry

Wet and drying ewes at or soon after weaning will help identify ewes that have not reared a lamb. If all ewes have been preg scanned before lambing, the dry ewes will be those who failed to rear a lamb. You will have your own criteria as to how strict you are at keeping on dry ewes or ewes that failed to rear (e.g. you might be easier on young ewes or if you had a very tough lambing period). This year did see some high scanning rates due to green feed at joining, but the lack of follow up rain to grow the required feed may have led to more lamb losses. If looking to reduce ewe numbers, taking out those that failed to rear a lamb are an obvious first choice.

Udder defects and Fit to Join project

A project called ‘Fit to Join’ looked at the impacts of udder defects on future lamb/ewe performance. They also found a surprising proportion of udder defects in the flocks they investigated. Mothers with a ‘bad’ udder had 21% higher lamb losses from scanning to marking. The farmers involved in the project were surprised at the number of ewes in the flock that had bad udders and results indicated that 8-10% could be culled in the first year. Interestingly, the timing of udder assessment is critical and can not be done when wet and drying at marking. The ideal time to assess udders is approximately one month after weaning as some ewes will develop mastitis from being weaned.

The project developed a simple ewe assessment tool to identify sheep that are at a high risk of failing to get in lamb and/or raise a lamb. Some simple videos and pictures to help with the assessment are available on the ‘Fit to Join’ website.

1. Assess the udder

Any ewe with an udder abnormality is an immediate cull. Abnormalities include malformed teats and abscesses/lumps around the teat or mammary glands. One of the farms involved in the trials found for every 100 ewes with ‘good’ udders there were 32 more lambs marked than from the ewes with ‘bad’ udders.

2. Assess ewe condition

For other traits they used a 2 strike out system to decide whether to cull based on body condition, lameness, age and mouth. For example, if an older ewe has a sound udder, is more than half a body condition score lighter than the mob average and her teeth are poor, then she would be considered a cull. However, if the ewe is in light condition and has no other problems then she can be kept for another year to give her the opportunity to improve.

Culling on mouths (dentition and teeth wear) has been shown to have a poor correlation to production. A better criterion is on body condition, as ewes that have been run in the same condition, have good body condition are obviously coping well whether or not they have teeth wear. Clearly ewes that have reared twins or multiples rather than singles will come out of lambing in lower condition, so it is important to cross check with scanning records to ensure twin bearing ewes are not compared to single bearing or dry ewes. The 2 strike system will help reduce the risks associated with culling otherwise productive ewes on the back of one criteria such as low body condition.

Age

Deciding on what age to cull ewes before they drop in production, is a balance between bringing in younger better genetics and optimising performance of the ewe flock (plus the cost/benefit if purchasing ewes).

Generally (and individual flocks will vary) mortality of ewes tends to increase at and beyond 7 years of age. As ewes get older, they are more prone to metabolic conditions such as hypocalcaemia and pregnancy toxaemia. Peak body weight is reached at about 6 years old in merinos and about a year earlier in maternal breeds. Wool production in merinos generally peaks around 3-4 year old.

When considering age profiles of your flock, the age at which ewes have their greatest lactation potential is worth considering. Ewes tend to increase milk production as they get older, generally peaking at around 3-4 years of age.

Noting that a 5 year old ewe would generally produce more milk than a maiden ewe. So, the maternal environment provided by a 5 year old ewe would be expected to foster higher lamb weaning weights than from a maiden ewe. To that end, if you are culling all the 5 year old ewes you are possibly impacting overall lamb turnoff weight – but that needs to be balanced against the rate of genetic gain, and improvements in growth potential from younger stock. Therefore, the age structure to maintain is a farm by farm decision.

In summary if considering culling ewes this year, there may be opportunity to strategically cull specific ewes to reduce feed requirements over summer/autumn, while maintaining higher levels of production into next year. Be sure to consider:

• did the ewe rear a lamb/s
• has she got a functional udder
• condition; lameness and age
• balance improved genetics of young stock versus production of mature animals
• wool production – if important
• visit the Fit to Join on MLA website to learn more about the project and how to assess ewes for future productivity and profit.