In the research flock ewes are shorn at housing and offered high feed-value grass silage until lambing. Post lambing ewes are turned out to pasture and grouped at approximately 20 ewes per paddock. After approximately one week these groups are amalgamated to groups of about 40 ewes.
A week later the groups are further amalgamated to yield final grazing groups of about 100 ewes and their lambs. Male lambs are not castrated. No concentrate supplementation is offered post turn out to ewes or lambs where the lambs are being reared as singles or twins. Ewes rearing three lambs are managed separately from these nursing singles and twins. Ewes rearing triplets receive 0.5kg concentrate daily for five weeks post lambing, while their lambs are offered up to 300g concentrate daily until weaning.
All lambs are treated for internal parasites at 5, 10 and 14 weeks of age. The treatment at 5 weeks is aimed at control of Nematodirus. The drench which will be administered at five and 10 weeks is levamasole based while the drench at 14 weeks (weaning) is an ivermectin.
Post weaning, all lambs are grazed together until drafted for slaughter. Lambs are drafted every three to four weeks post-weaning. After every second draft the remaining lambs are treated with anthelmintic (an ivermectin) for internal parasites. Male and female lambs are grazed in separate groups from mid-September until drafting.
This year ewes that were scanned to be carrying singles, twins and triplets received a total of 17, 23 and 29kg concentrate, respectively, during late pregnancy. Post-lambing ewes were turned out to pasture that had a mean sward height of 6.1cm.
Performance to weaning
The post-lambing management system described above has been the same over the last 10 years. Lamb weaning weight for the years 2007 to 2016 is presented in Figure 1.
This data includes all lambs, regardless of dietary treatments offered to their dams during the rearing phase or during pregnancy. The data presented are for lambs born and reared as either singles, twins or triplets.
On average over the 10 years singles, twins and triplets weighed 37.0, 30.6 and 31.1kg at weaning and had daily live-weight gains of 320, 265 and 277g from birth to weaning.
While lamb performance varied among years the performance in any year was within 0.75kg of the overall average (in the case of twins) with the exception of 2007 and 2009 - thus consistent performance is achievable from grass based systems. The differences in lamb performance between grazing seasons reflects year effects but also other factors such as dietary treatments the ewes were offered during pregnancy; this flock has been used to evaluate a wide difference in nutritional regime over the period from 2007 to 2016. Previous studies at Athenry have shown that each 1kg increase in birth weight increased weaning weight by 3.2kg. Thus, any pregnancy nutrition that changes birth weight will have a significant impact on weaning weight.
Nevertheless, the evidence shows that whilst lamb performance to weaning varied among years all lambs were drafted for slaughter prior to the end of the grazing season (early-December).
The ewes that were rearing singles and twins were managed at pasture in three groups during 2016. Each group was managed in a rotational grazing system. The mean pre- and post-grazing sward heights are presented in Figure 2. Swards were grazed to a low-post grazing height early in the grazing season (March, April).
Then, as the grazing season progressed post-grazing sward height increased. Mean post-grazing sward height was 3.7, 4.2, 5.5 and 6.6cm in March, April, May and June, respectively. Grazing to a low sward height early in the grazing season results in delayed stem elongation and this ensures the production of more leaf and, thus, herbage of higher digestibility and intake characteristics. Grazing to a low sward height, particularly during the last four to six weeks prior to weaning impair lamb performance because the lambs are forced to graze herbage in the lower part of the sward horizon, which is lower in digestibility.
Also, as weaning time approaches the proportion of the lamb's nutrient intake accounted for by milk declines rapidly and they rely more and more on pasture for nutrition. Sward height pre-grazing also increased as the season progressed: 6.3, 7.3, 10.2 and 10cm for March, April, May and June, respectively. the mean mass of herbage dry matter pre-grazing was 840, 990, 1,860 and 1,800kg/ha for March, April, May and June, respectively.
Performance in 2016
Lambs born and reared as singles, twins or triplets were 39.5, 31.9 and 29.4kg, respectively, at weaning. Twins and triplets were a similar weight and age at drafting. Lambs born and reared as singles were drafted for slaughter five weeks earlier than twins and triplets.
The data in Table 1 implies that age at drafting for any particular flock will be influenced by flock productivity, i.e. the number of lambs reared per ewe joined.
Drafting pattern in 2016
No lambs are drafted prior to weaning at Athenry to enable the collection of growth data to weaning on every lamb reared. Thus drafting commences at weaning. During June, July, August, and subsequently ram lambs are drafted at 43, 46, 47 and 48kg, while ewe lambs are drafted at 42, 45 46 and 47kg, respectively. The drafting pattern for the flock is presented in Figure 3. By the time all lambs were weaned in late June 8pc of the lambs had been drafted.
By early August and mid-September 39 and 63pc of the lambs were drafted for slaughter. The final draft occurred on 28 November. The effects of rearing type on drafting pattern are presented in Figure 4. Singles were drafted earlier than twins and triplets. By mid-July 59pc of singles were drafted compared to only 21 and 18pc for twins and triplets respectively.
However, by mid-October similar proportion of singles twins and triplets had been drafted. The drafting pattern for twins and triplets were similar.
The data presented in Figure 4 implies that in flocks where ewe productivity (lambs reared per ewe joined) is low (many singles) the proportion of the lambs drafted by mid-July ought to be high.
As we are half way through the annual sheep production cycle, and nearing the end of the busy lambing season, it is a good time for some reflection
Lamb performance to slaughter is impacted by plane of nutrition prior to and post birth
At Athenry all lambs are drafted prior to the end of the grazing season.
Drafting pattern is influenced by ewe productivity - by mid-July 59pc of singles but only 21pc of twins were drafted
Consistent performance is achievable from grass-based systems.
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Dr Tim Keady is principal research scientist at the Animal and Grassland Research and Innovation Centre, Teagasc, Athenry, Co Galway; Noel McNamara is the farm manager at the Teagasc Research Farm in Athenry