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The Irish and New Zealand Across Country Comparison (INZAC) flocks are in their second full-year production cycle in Teagasc, Athenry. Lambing is as good as finished, with the last few repeat ewes lambing over the last week. The lambing season went well – it commenced on 25 February, with 83% of ewes lambing in the first two weeks.
The recent sheep industry meeting hosted by Teagasc and Sheep Ireland got an update of performance to date and, while it is still early days, it is the New Zealand Suffolk and Texel ewes that are edging in front in terms of performance.
Delivering a background to the trial, researcher with the project Fiona McGovern reminded attendees that there are three main objectives.
The first is to validate the Irish replacement genetic sheep index. This is being achieved by comparing the performance of a flock of 30 five-star high-genetic-merit (HGM) purebred Suffolk ewes and 30 five-star HGM purebred Texel ewes (pictured above) to similar flocks of one-star low-genetic-merit (LGM) ewes (pictured below).
The main outcomes that should materialise over the course of the four-year project is five-star ewes recording less lambing difficulty, more lambs produced (combination of 7% fewer deaths and 0.13 more lambs per ewe), lighter mature weight of ewes and lambs delivering 2.5kg extra weaning weight.
The second objective is to compare the performance of the fiver-star, or elite, Irish ewes with the flock of 30 elite New Zealand Suffolk ewes and 30 elite New Zealand Texel ewes, with the same parameters used as described above.
The last objective is to create genetic linkages between Ireland and New Zealand to build on these initial cross-country evaluations and also continue to develop genomic selection.
Initial results
As mentioned earlier, lambing progressed favourably. Artificially inseminating ewes in two batches over the space of a week resulted in 83% of ewes lambing in the first two weeks, which will allow performance to be compared accurately by removing production differences that may otherwise occur if there was a significant variation in the environmental conditions lambs were born into. Table 1 details the effect of ewe genotype on pre-partum performance.
Looking back to the breeding update last October, New Zealand ewes had a body condition score of 3.9, HGM Irish ewes averaged 3.8, while LGM ewes averaged 3.4 BCS.
The New Zealand ewes have recorded a slightly higher barren rate in the last two years, with Fiona explaining that the barren rate overall is higher than with natural mating and is a consequence of using AI to try to eliminate environmental variance.
While the barren rate may have been higher, the New Zealand ewes compensated with a higher scanning rate, with the difference between HGM and LGM ewes also heading in the right direction to validate the index.
Lambing performance
Provisional lambing results collated to date are detailed in Table 2. Fiona reminds us that a different picture could develop when further years of data are available, but one parameter that she says is unlikely to change is the lower lamb mortality of lambs born to New Zealand ewes.
“What we have seen so far is that these ewes seem to be better mothers and lambs exhibit more vigour and are up to suckle faster. I’d be surprised if there wasn’t a difference [in mortality] at the end of the four years,” she said.
Irish ewes required more intervention at lambing, with higher levels of dystocia recorded and the HGM ewes recording a much higher level of 13%.
The effect of ewe genotype on lamb performance pre-weaning is detailed in Table 3 for 2016. Lambs born to the elite Irish ewes recorded higher performance in early lactation, but it should be also remembered that there was a lower average litter size than the New Zealand-born lambs.
This reduced in the period from six to 14 weeks, with the New Zealand Suffolk and Texel lambs recording the highest pre-weaning performance.
No meals are fed at grass to ewes or lambs with the aim to maximise performance in a grass-based system utilising excellent grassland management.
The flock is collecting a multitude of performance records, with two traits currently recorded being the milk yield of ewes and ewe intake.
Milk yield is being determined using a weigh-suckle-weigh technique, whereby lambs are temporarily removed from their ewes and then weighed before and after suckling to determine milk yield.
“Results are only being collected, but we can see that, on average, it looks like one-star Irish ewes are producing about a litre less milk than the five-star Irish ewes, which explains the significant difference in performance in early lactation,” said Fiona.
Drafting rates
The higher pre-weaning performance of New Zealand Suffolk and Texel lambs (pictured below)continued post-weaning, as detailed in Table 4. Ninety-six per cent of these lambs were drafted out of the system at the target liveweight, compared with 82% from HGM Irish ewes and just 69% from the LGM flock.
All of the New Zealand lambs were drafted out of the system by the end of September, with only a small percentage requiring meal supplementation.
Not all lambs are being slaughtered, with a selection of ram lambs identified for breeding purposes.
While drafted out of the project, these rams are present in Teagasc Athenry and Fiona says some will be used for the 2017 breeding season on commercial farms such as the Teagasc BETTER farm sheep programme, which will enable performance to be analysed in a wider environment, with more records leading to higher accuracy of data.
Grassland management
Henry Walsh is the Teagasc technician working with the INZAC flock. He reported excellent grassland performance in 2016, with the total volume of herbage grown recorded at 14.7t DM/ha (11.35t/ha grazed and 3.36t/ha silage).
The high performance is being driven by a number of factors. Each grazing group of 60 ewes (30 Suffolk and 30 Texel) has access to 5ha, giving a stocking rate of 12 ewes/ha with an overall nitrogen allocation of 150kg N/ha/year.
Each farmlet is divided into four permanent divisions and Henry says the ability to sub-divide these temporarily with electric fencing is the secret to capitalising on higher growth rates during the peak growing season.
The aim is to enter paddocks at a pre-grazing height of 7cm to 8cm and graze out paddocks to 4cm, with surplus grass taken out of the rotation as the season progresses as baled silage.
“This worked excellently in 2016, which was a good grass year after a slow start. We utilised 99% of grass available from March to August and this was made possible by sticking to pre- and post-grazing heights, taking paddocks out of the system and above all by keeping on top of grassland management in the critical peak growth period.”
The farm has just entered its second grazing rotation. Lower temperatures have eased growth to 34kg DM/ha while 20% of each area has also been removed for silage, leaving 18 days grazing ahead.
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