Tony Leggett

More than nine out of every 10 ewes were either prematurely culled or died before they reached year-six weaning, a Massey University longevity project has shown.

Massey University veterinarian and researcher Kate Griffiths is researching the causes of ewe wastage on New Zealand farms.

The project was run by Massey University veterinarians Kate Griffiths and Anne Ridler to investigate the extent and timing of ewe wastage and reasons for reduced longevity.

Griffiths says it is important to note that wastage covers both ewe mortality and premature culling.

“Our data shows that by the end of year six, typically when farmers would think to cull for age, from the 13,142 ewe lambs enrolled in the trial, more than 90% had been wasted,” she says.

That level of wastage represents a massive cost for sheep farmers because they need to retain more ewe lambs as replacements, so they have fewer to slaughter, and they miss out on higher lamb production from retaining more older ewes in their flock and not being able to mate more ewes to terminal sires.

‘They are shocked when you first say that number, but when you start working back from what they are losing annually, through mortality and culling decisions, it all makes sense.’

Annual ewe mortality rates (dead and missing presumed dead ewes) were typically in the range of 8-12%, however in some years they were lower or higher than this in some study flocks.

Griffiths says the 90% wastage figure has surprised farmers when she’s presented her findings at recent seminars around the country.

“They are shocked when you first say that number, but when you start working back from what they are losing annually, through mortality and culling decisions, it all makes sense,” she says.

“When you consider that some farmers have replacement rates of 25-35%, and even up to 40%, it becomes clearer,” she says.

The study was funded by Beef + Lamb NZ, C Alma Baker Trust and the Massey University Research Fund.

Data was collected at key points over the ewe lambs’ lifetime.

Across the enrolled ewe lambs in the project, 50.4% were culled before reaching six years of age and 40% were either dead or missing on farm by that time.

Almost all the ewe hoggets enrolled were mated as hoggets, compared with only about 40% of hoggets mated nationally. Griffiths says there was not enough data to consider any breed differences. Most of the ewe hoggets in the project were Romney and Romney-cross types.

For the project, data on ewe weights, body condition score, reproductive data was collected at four times during the year – pre-mating, scanning, set-stocking and weaning.

The farm owners managed their flocks as normal but were asked to record when and why ewes were culled.

Some of the flocks culled heavily on hogget reproductive performance (dry at scanning or wet-dry at docking), while others retained hoggets regardless of reproductive performance.

Griffiths says management at both the hogget and two-tooth stage, to ensure they get in lamb and preferably rear that lamb, will have a big impact on wastage rate in a flock.

“If you’ve made a decision to cull wet-dry hoggets, then you’re going to lose a large number of sheep at that age,” Ridler says.

“Based on farms I’ve visited, having 30% wet-dry ewe hoggets is not uncommon. A lot of those sheep are probably just unlucky. For example, they have given birth during a storm and because their lamb died, they may be culled,” she says.

When they checked one of the farms that kept wet-dry ewe hoggets they found these same sheep were not wet-dry as two tooths, so culling at the ewe hogget stage may be considered costly.

There are flocks in the project where there is potential for up to 50% of ewe hoggets not to make it through to mating as a two-tooth because they are culled for not getting in lamb or being wet-dry as a ewe hogget, plus annual mortality as a hogget.

The next stage of the project will include a deeper investigation of culling decisions and finding out more about why ewes are dying in the paddock.

A Massey student is studying 1700 ewes lambing on 260ha of hill country to determine the cause of death for every ewe and lamb that dies over the lambing period. She is using a combination of driving and walking to cover the area, which is taking 5-6 hours every day.

“She won’t find them all, but she will go very close. So far, more than half of the ewes found near death are cast, so she is saving a lot too. Bearings and dystocia are the other main reasons for ewes dying on this property over lambing,” Ridler says.

“We’ve been trying to use a drone to cover the area more efficiently and disturb ewes less, but it’s windy in spring on most New Zealand farms so it’s only useful in gullies or areas that are out of the wind,” she says.

The results of this ewe death study will be released early next year. Ridler says it is one farm in one year, but it should provide some insight into the challenges of collecting this type of data across larger areas on multiple farms.

A cast ewe carrying triplets is valuable – perhaps worth $500. The challenge is how to balance out the impact of disturbing other ewes at lambing time to save one valuable ewe.

PhD student Lydia Farrell is also modelling the cost to the farm business of different replacement rates to provide insight into the economic impact of higher wastage rates.


  • Costs of higher wastage in ewe flocks
  • Requires higher retention of ewe lambs to replace lost older ewes
  • Less ewes available for mating to terminal sires
  • Lower lambing performance from high % young ewes in flock
  • Biosecurity and quality risks when buying in replacement ewes or ewe hoggets
  • More replacement ewe hoggets means bigger high priority mob to manage