The Romney dominates the ewe type both directly and indirectly through the use of Coopworth and Perendale bloodlines. The Romney breed also contributes to the composite breeds to varying extents which have increased in importance recently in New Zealand.
Imported breeds such as the Finn and the Texel have also gained some traction as contributors to these composites.
In response to the growing popularity of the composites, the Romney breed has engaged in breeding programmes to improve prolificacy, while maintaining its suitability for New Zealand's undulating landscape.
Prof Kenyon said the increase in carcass output per head would probably level off in the coming years due to natural biological limits in flocks. Indeed, the downside of increased prolificacy, where higher numbers of triplets are born in extensive lambing systems, was evident with increases in lamb mortality and reduced ewe longevity.
So what is the way forward? According to Prof Kenyon, it's by increasing the carcass production per ewe lifetime. He presented four theoretical ways to achieve this.
The first option is certainly more theoretical than practical – breeding all year round, as already happens in pig and poultry sectors that now dominate meat consumption.
This approach is attractive in theory as New Zealand's lamb supply is very seasonal, concentrated into the January to April period.
The Cornell star system was discussed but the resounding feeling was that it is not suitable for pasture-based systems like New Zealand and Ireland.
The second option discussed was increasing lambs per litter. The easy gains have already been made in this regard, and although there is still considerable national variation, it is questionable whether the farmers at the lower end of the range will increase, or indeed want to increase lambing percentage.
Breeding ewe lambs was described as a potential strategy to increase lifetime performance.
The average lambing percentage for New Zealand ewe lambs is low at 50-70pc, with the range of 20-120pc even more troubling.
At the moment these lambs make very little contribution to the overall numbers of New Zealand lamb, accounting for just 4-5pc of total lambs slaughtered annually.
When a farmer is considering mating ewe lambs a couple of key factors must be considered.
Firstly, only the ewe lambs that have reached the target liveweight at mating time should be bred.
This target varies depending on the breed of the ewe lamb. The ewe lambs that do not reach this target liveweight must not be mated. Instead, they should be carried over and mated the following year.
Another reason for holding off on mating ewe lambs is feed scarcity. There must also be enough feed available to allow the mated ewe lambs to continue to grow during pregnancy.
If a feed shortage is predicted, then ewe lambs should not be mated.
A figure which really struck home with me in terms of feed requirements was that the extra feed required to carry eight pregnant ewe lambs compared to eight dry ewe lambs was equivalent to one mature ewe over the winter.
So from a feed point of view it would be more efficient to cull an unproductive ewe and carry eight pregnant ewe lambs instead. For a mature liveweight of 65kg the target liveweight at mating was 40kg.
The final idea outlined to increase the output of lamb during a ewe's lifetime was to increase her longevity within the flock.
There is 8-10pc annual wastage in the New Zealand flock. It is also likely that the cause of these deaths is also contributing to an underlying reduction in animal performance.
This is often not detected at farm level.
No doubt nutrition and the complete lack of supplementation in some cases has a role to play here. However, a full analysis of the causal factors is required.
The latter two options are where there appears to be the most scope for improvement in the New Zealand flock, though issues remain to be addressed about the persistency of animals bred as ewe lambs within the flock.
One issue which was not touched upon in the session was post-partum lamb performance, especially post-weaning performance.
When questioned from the floor, we heard that post-weaning lamb performance is often less than 100g/hd/ day, which is a significant drag on costs.
For a growing lamb, 60pc of what it consumes each day goes towards maintenance. Clearly, getting them finished early will reduce the cost of finishing.
A note of caution was stressed by Prof Kenyon in relation to improving poor performing lambs in the national flock, as it would increase lamb supply even more, placing further pressure on price.