Performance for the year to date in the Irish and New Zealand Across Country (INZAC) trial is progressing as expected, with high-genetic merit New Zealand and Irish Suffolk and Texel ewes outperforming low-genetic merit Suffolk and Texel ewes.

This is reflected most recently in daily liveweight performance, which in turn is driving drafting rates.

Up to the end of last week, there were approximately 45% of lambs drafted in both the high-genetic merit New Zealand and Irish groups, compared with just 20% in the low-genetic merit Irish group.

This trend of superior performance in the high-genetic merit groups is likely to continue, although variation in liveweight performance in recent weeks may see the progeny of New Zealand ewes push ahead.

Daily weight gain

This is stemming from these lambs achieving an average daily weight gain of 200g since weaning, ahead of the high-genetic merit Irish lambs, which have gained 180g to 190g on average, and a long way ahead of the low-genetic merit progeny, which have gained just 150g on average since weaning.

The performance in the high-genetic merit groups has been positive in 2017 and Fiona McGovern, lead researcher with the trial, says this is being driven by sheep receiving no setbacks in 2017.

“The year has been close to perfect. Grass supplies have been running ahead of demand all year, giving ewes and lambs a great opportunity to maximise performance. When a dip in growth did come a few weeks ago, with weekly growth rates briefly falling to 30kg DM/ha, it occurred at weaning, which was a positive, as ewes were tightened for drying off", he said.

Drafting lambs

Drafting is currently taking place every two weeks, with the average liveweight for drafting currently standing at 45kg, after rising by 1kg each month since May.

Once lambs hit this weight, they are drafted out of their grazing groups, but are not initially slaughtered, as the aim is to select animals with breeding potential.

This is done on a combination of assessing physical attributes and the animal’s genetics, with ultrasound scanning for muscle and fat depth that was carried out two weeks ago a key component.

Suitable ewe lambs will be used as flock replacements, while selected ram lambs will be used for semen collection for AI or placed in commercial flocks, so performance can be accessed in a wider commercial environment.

Fiona says that the aim this autumn is to get linkages developed with a network of farmers in the Teagasc BETTER farm sheep programme.

The absence of slaughter performance is one aspect of the trial that Fiona says will be addressed at a later stage.

One option that is likely once sufficient numbers of ewes and rams have been selected for breeding is having one year of the trial where lambs are slaughtered as they are drafted.

For now, ultrasound scanning is providing a useful predictor.

There is slaughter performance coming from small numbers of animals deemed not suitable for retaining for breeding (once ultrasound scanning has been completed), but this information is not relevant, as these animals are, in cases, slaughtered a significant length of time after drafting.

Grassland management

As mentioned previously, grass growth has been favourable for the year to date. Current growth rates are running at about 60kg DM/ha and Teagasc technician with the flock Henry Walsh says each of the 5ha farmlets for each grazing group is continuing to produce surplus grass.

“We have received very high levels of rainfall in the last two weeks, but it hasn’t affected growth too much, with soil temperatures remaining high. Ground has got a bit wetter, but utilisation is still pretty good, with lambs grazing ahead of ewes.

“There may still be a couple of half-paddocks that may be pulled out for silage, but this will depend on how growth is. We will soon be starting to build covers to deal with rising demand as ewes approach breeding.”

Fiona says that even where ewes are being used to graze out paddocks, their condition is improving, with favourable growth rates boosting intake.

This has seen ewes quickly recover in condition, with the average body condition score of ewes ranging around the 3.5 mark.

This is on the strong side of where Fiona wants the ewes to be and current management is aimed at trying to offer ewes a maintenance diet with grass allocated at about 1kg DM intake. Strategic use of topping is also being used to clean out paddocks and promote excellent-quality grass regrowth.

Overall performance

While the INZAC trial is still only in year two of at least four years of trial work, New Zealand ewes continue to edge ahead of Irish ewes in the grass-based system.

Table 1 details reproductive and lambing performance and, as can be seen, New Zealand ewes are outperforming their Irish counterparts in all traits, with the exception of lamb mortality.

The high-genetic merit Irish ewes achieved positive performance here, although they did require much more intervention at lambing.

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