The Irish and New Zealand across-breed comparison trial (INZAC for short) is coming to the end of its fourth production cycle and the conclusion of the first step of the trial. The trial was set up to compare the performance of high genetic merit Irish Suffolk and Texel genetics against their New Zealand comrades, while it also included a low genetic merit Irish Suffolk and Texel flock with the focus of validating the Sheep Ireland replacement index.

From the first production cycle the New Zealand (NZ) bred ewes edged out in front of the Irish ewes in the grass-based production system where ewes are stocked at 12 ewes/ha in a rotational grazing system utilising an annual chemical nitrogen input of 130kg N/ha or 11kg N per ewe. Nicola Fetherstone, PhD student working with the trial, says this remains the case.

Table 1 details the effect of ewe genetic merit on reproductive performance. All ewes were synchronised (receiving 400mg PMSG) and inseminated through laparoscopic AI, with repeats given two cycles to conceive.

The NZ ewes had a higher percentage holding to first service with no significant difference to the in-lamb rate. The NZ ewes excelled in terms of litter size produced with no significant difference between the high and low genetic merit Irish ewes.

Lambing traits

The effect of ewe genetic merit on lambing traits is detailed in Table 2. There was no significant difference across all groups in the birth weight of lambs or ewe mothering ability. Again the NZ ewes outperformed their Irish comrades in lambing difficulty, with 15% recording a difficult manual or veterinary-assisted birth. This is slightly higher than that recorded in New Zealand but it may be a fact that ewes under Irish conditions were fed better and also housed, which could have contributed to these levels. One in four Irish ewes had to be handled at lambing compared to one in six for the NZ groups with no difference between these. The lower level of dystocia in NZ ewes also led to 2% lower lamb mortality.

Weaning rate

The higher litter size and lower mortality of the NZ ewes obviously laid a foundation for a higher weaning rate. The NZ Suffolk and Texel ewes had a weaning rate of 1.54 lambs per ewe joined while the high Irish ewes weaned 1.45 lambs and the low genetic merit ewes weaned 1.34 lambs. As well as achieving a higher weaning rate, progeny of NZ ewes also performed better up to weaning.

A New Zealand Texel ram in the foreground and three New Zealand Suffolk rams in the background give an example of the breed.

There was no significant difference in the 40-day weight of lambs, with NZ lambs weighing 17kg on average while the two Irish groups averaged 16.8kg. The weaning weight of NZ born lambs was 34.5kg, while the high Irish group progeny had an average weaning weight of 32.7kg and the low group was recorded at 31.9kg.

Days to slaughter

The higher performance of NZ born lambs underpinned the shortest days-to-slaughter period. Progeny were drafted at an average of 160 days of age having achieved an average gain of 256g/day. The high Irish group had a days-to-slaughter figure of 165 days having achieved an average daily gain of 245g, while the low genetic merit progeny had an average days-to-slaughter figure of 175 days and an average lifetime daily gain of 232g.

The New Zealand Suffolk and Texel genetics differ from the Irish genetics with rams and ewes possessing lighter bone.

It should be noted that lambs are drafted when they reach a given liveweight that is predicted to give a target carcase weight of 21kg as a high percentage of male and female lambs are kept as replacements for use in other linked flocks. The drafting weight increased by 1kg liveweight per month and started at 43kg in June. The low number of progeny slaughtered means a question still remains as to the actual slaughter performance of lambs in the trial but more information will start to filter through from the second phase of the trial with higher numbers of lambs being slaughtered and more slaughter records coming through from commercial flocks where these genetics are now being used.

Higher milk yield

Nicola explains that milk yield analysis using a weigh-suckle-weigh technique at four and six weeks into lactation shows a higher milk yield from NZ ewes underpinning the higher performance. These ewes recorded an average milk yield of 2.1l per day compared to 1.9l in the high group and 1.7l in the low genetic merit group. Nicola says analysis of body condition score at key time frames shows that this higher milk yield is likely to be helped by ewes utilising body condition to drive milk yield and being more efficient with grass intake post-partum.

NZ ewes had an average condition score of 3.25 at lambing, which dropped slightly to shy of 3.2 at six weeks post-partum before recovering in week 10. This compares to the Irish groups which lambed at a BCS of 3.1 with the average BCS increasing over the next 10 weeks. Table 3 shows the average level of grass intake for three production periods. The NZ ewes have a higher intake at 10 weeks than the high Irish group and consume significantly more grass in the dry period. This is used to drive a significant increase of about half a body condition score from weaning to mating, leaving ewes 0.2 of a BCS unit higher than the Irish ewes at mating.

Index validation

Looking at the second aim of the project and index validation, Teagasc geneticist Noirin McHugh says the trial has delivered on its objective of validating the index with the high index Irish ewes recording higher performance than the low genetic merit group.

A re-ranking of the index has reduced the average €uro-Star rating of the high genetic merit Suffolk ewes. This group will be reassessed ahead of this year’s breeding, with some replacements required to bring the average rating back to five-star animals.

The next phase of the study will delve deeper into important production traits such as ewe longevity, ewe lifetime efficiency, the replacement rate, number of lambs produced over a ewe’s lifetime, reasons for lambing assistance and labour required around lambing and thereafter. Health traits such as litter viability, IgG levels, dagg scores and individual faecal egg counts and overall mortality will also be assessed in greater detail while as mentioned earlier there will be a much greater focus on slaughter performance and carcase data.

Purchase of shearling rams

The flock is now firmly established in Teagasc Athenry and an opportunity has arisen to offer in the region of 10 surplus New Zealand Texel and New Zealand Suffolk rams for sale to the Irish sheep industry. All shearling or hogget rams were born between 27 February and 18 April 2018 and have been produced in a grass-based system.

The selling of rams will be undertaken in two steps. Farmers must meet a small number of selection criteria including possessing a minimum flock size of 50 ewes, have Suffolk or Texel genetics in their current flock, demonstrate that they have been carrying out a level of performance recording in their flock and going forward agree to record all subsequent data on sires and their progeny through Sheep Ireland.

While not a requirement, it would be beneficial if some female progeny were retained as replacements.

Interested parties who meet this criteria should submit an expression of interest letter to Breeding and Genetics, Teagasc Animal and Bioscience Research and Innovation Centre, Mellows Campus, Athenry, Co Galway by Friday 6 September 2019. The expression of interest should include your herd number and contact details.

Where the number of expressions of interest exceeds the number of rams available, a lottery system will be operated whereby all potential purchasers will be drawn at random and ranked on their selection from the lottery. All potential purchasers will be informed of their ranking in the selection of rams and given details of when they will be able to come to Teagasc Athenry to view and select a ram along with information on the back ancestry of rams and the €uro-Star ratings. The selling price of all rams is €500 and is non-negotiable.