‘New Zealand is achieving 3 times the rate of genetic gain to Ireland at present’

During Tuesday evening’s virtual Teagasc Sheep Conference, Nicola Featherstone, a Walsh Scholar, gave an update on the INZAC trial in Athenry.

INZAC – an Irish versus New Zealand animal comparison – has been ongoing since 2016 and the reason for the comparison is due to the similarities between both the Irish and New Zealand production systems.

New Zealand is similar to Ireland in that it is grass-based and has a seasonal lambing period which leads to a volatile sheep industry where lamb is plentiful in the summer months and in short supply over the winter period. It is also a predominately export-focused market, where 39% of its sheepmeat goes to China alone.

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Nicola said that even though Ireland and New Zealand have similar production systems and a similar breeding objective, that New Zealand is achieving three times the rate of genetic gain to Ireland at present.

Nicola said that the INZAC trial was established to validate the Irish replacement index and to compare the difference between Irish and New Zealand ewe genetics. The INZAC flock is comprised of 180 ewes.

Each group is broken up evenly between Suffolk and Texel ewes – all of which are pedigree animals.

The breakdown of the flock is as follows:  

  • 60 elite New Zealand genetics (imported in 2013 and 2014);
  • 60 high Irish genetics (5-star on the replacement index);
  • 60 low Irish genetics (1-star on the replacement index).

Flock management

Speaking on the management of the flock, Nicola said: “So for the breeding season, all the ewes are synchronised and laparoscopic AI’d.

“Ewes are let to rams for two repeat cycles, which gives us a mean lambing date of March 8. Ewes are housed in December and are winter shorn.

“Records are taken at lambing. The maximum rearing type is two lambs per ewe. Any triplet lambs are artificially reared or cross-fostered onto a ewe within the same genetic merit group.

“48 hours after lambing, ewes and their lambs are let out to grass. Each group is allocated a 5ha block and divided up into paddocks which gives us a stocking rate of 12/ha using a rotational grazing system.”

Results

Reproductive traits

Nicola added: “The results from conception rates show that an average of 78% was achieved across four years from laparoscopic AI.

“As previously mentioned, ewes were let to rams for two repeat cycles, so this resulted in a barren rate of 7.6% across the three groups.

When we look at litter size, there is a significant difference between that reported from the New Zealand and low Irish animals.

“This trend follows on to weaning rate, where New Zealand and high Irish ewes reared a greater number of lambs in comparison to low Irish animals, at 1.34 for New Zealand, 1.26 for high Irish and 1.11 for low Irish ewes. It is important to note that this trait is reported as the number of lambs reared per ewe joined and doesn’t include any artificially reared lambs.

“We also looked at ewe survival. Here we looked at the proportion of ewes that survived from one year to the next. 70.4% of the New Zealand ewes survived from year-to-year, in comparison to 64% and 63% for the high and low Irish ewes.

“The difference between the New Zealand and Irish ewes equated to up to 6.6 ewes in every hundred each year.”

Lambing traits

Speaking on the findings with regards to lambing traits, Nicola said: “First up is lambing difficulty. New Zealand ewes were significantly easier lambed.

These results aren’t far from what we expected, as New Zealand animals come from an outdoor production system, where minimal assistance was offered at lambing.

“In terms of ewe mothering ability, there was no difference between the three groups – averaging out at 76%. This was scored on how easy the ewe followed her lambs from a group pen to an individual pen.

“We also looked at litter vigour [how easy the lamb(s) can get up and suckle themselves]. 51% of New Zealand lambs required assistance suckling, while 65% of high Irish lambs and 69% of low Irish lambs required help. Mortality in the first 24 hours after birth ranged from 4.7% to 6.7%.”

Lamb performance

Looking at lamb performance between the groups, in particular lamb growth and drafting, Nicola added: “At birth, there was no difference in the birth weight between the three groups (5.3kg). However, as the lamb grew from birth to 40 days, New Zealand lambs grew at a weight of 312g/day, while both the high and low Irish lambs grew at 305g/day and 303g/day, respectively.

“From 40 days to weaning, the liveweight at 40 days averaged at 17.1kg, with no difference seen between the three groups.

When we look at weaning to drafting, New Zealand lambs averaged 32.9kg, high Irish lambs reached 31.9kg and low Irish lambs were 31.7kg. New Zealand lambs grew at 243g/day, while both high and low Irish lambs grew at 215g/day and 193g/day respectively.

“This then had a knock-on effect to the days to drafting [it’s important to note many lambs are kept as replacements; not many are slaughtered].

“There was a 13-day difference between New Zealand and low Irish lambs when it came to hitting their targets and being drafted for slaughter.

“Because we don’t kill many lambs, we ultrasound scan lambs as a proxy to see how they would perform for carcass conformation and fat score. The results showed that the New Zealand animals scored greater than both Irish groups.”

Productivity performance

Nicola explained: “Over a four-year period, in terms of the total number of lambs born, the difference between New Zealand and low Irish ewes was 0.7 lambs.

This trend also follows on for the number of lambs reared per ewe. Again, the difference between New Zealand and low Irish ewes was 0.43 lambs and a difference of 0.35 between the high and low Irish ewes.

“[Ewe liveweight : Litter liveweight] 40 days post-lambing, New Zealand and high Irish ewes produced 260g of lamb per kilo of their own liveweight, while the low Irish animals produced 213g.

“If we take three ewes weighing 75kg, the difference between the New Zealand and low Irish animals equates to 3.6kg in litter liveweight at 40 days.”

Summary

Summarising the results, Nicola concluded by saying: “New Zealand ewes are superior when it comes to litter size in comparison to the two Irish groups. However, for the number of lambs reared, New Zealand and high Irish ewes are superior to low Irish animals.

“When we group lambing traits together, New Zealand ewes are superior to both Irish groups in terms of litter vigour and lambing difficulty.

“In terms of lamb growth, both New Zealand and high Irish animals performed quite well, particularly post-weaning.

“Finally, efficiency traits such as total lambs born and reared, liveweight and intake comparison showed that New Zealand and high Irish animals performed significantly better than low Irish animals.”