1. Introduction
Increasing lamb production can improve the profitability of sheep enterprises, especially for non-Merino sheep and when sheep meat prices are high [
1,
2]. Lamb marking rates in Australia have increased by more than 10% over the last 15 years [
3]. This has resulted from the widespread adoption of practices to improve ewe nutrition before joining and during pregnancy [
4,
5], improved management during lambing [
6,
7,
8] and increased use of sires with higher breeding values for the number of lambs born and weaned. In addition, there has been significant displacement of Merino sheep by more fecund maternal ewe types [
9]. These increases in fecundity are associated with an increase in the proportion of multiple-bearing ewes, including those carrying triplets [
10], which can result in higher rates of mortality of both ewes and lambs [
11]. High rates of mortality of triplet-bearing ewes and their lambs limit the potential productivity gains and is an animal welfare issue.
Triplet lambs are born lighter, are more metabolically challenged, have lower body temperature and impaired behavioural development, and receive less colostrum and milk than their twin counterparts. Combined, these result in higher rates of mortality of triplet-born lambs [
11]. Kenyon et al. [
11] reported that the average birthweight of triplet-born lambs was 66% and 81% that of the birthweight of single- and twin-born lambs, and the average mortality rates of single-, twin- and triplet-born lambs were 10%, 15% and 33%, respectively. Triplet-bearing ewes are under greater nutritional stress in late pregnancy than twin-bearing ewes, as their increased nutritional demand is generally not matched by an increase in nutrient intake [
11]. This nutritional stress also contributes to higher mortality of triplet-bearing ewes compared to single- and twin-bearing ewes [
12]. There is, however, a lack of robust data on the magnitude and cause of mortality for triplet-bearing ewes and their lambs, particularly in Australia.
Management guidelines based on achieving ewe condition score, feed-on-offer (FOO) or mob size targets at lambing have been developed for single- and twin-bearing Merino and non-Merino ewes in Australia [
1,
13,
14]. However, targets for triplet-bearing ewes are unknown. To develop these targets, it is likely that further research is needed to examine the impacts of ewe condition score, FOO and mob size at lambing on the survival of the triplet-bearing ewe and her lambs [
11]. In addition, more knowledge of the potential impacts of shelter, other paddock characteristics and human intervention are required. There appears to have been no attempt to date to survey the management practices for triplet-bearing ewes that have already been adopted by sheep producers in Australia, nor a formal research-needs analysis based upon direct producer input. This study aimed to (i) identify current practices adopted for the management of triplet-bearing ewes; (ii) quantify the mortality of triplet-bearing ewes and their lambs on commercial farms in Australia; and (iii) identify research priorities to improve the survival of triplet-bearing ewes and their lambs from producer consultation.
4. Discussion
Consultation with sheep producers that had previously identified and differentially managed at least some triplet-bearing ewes indicated that reducing the mortality of triplet-bearing ewes was a high priority. The average mortality of triplet-bearing ewes from the benchmarking surveys was reported to be 6.4%, which was double that for twin-bearing ewes and four times that for single-bearing ewes. To our knowledge, this is the first study to quantify the mortality of triplet-bearing ewes on commercial farms across southern Australia. Kleemann et al. [
12] reported an average mortality of 12% for triplet-bearing ewes across three years at a single research site, which is within the range for flocks in our study. As expected, the mortality of triplet-bearing ewes was strongly correlated with the survival of triplet-born lambs, whereas the correlation was weaker for twin- and single-bearing ewes and lambs. Indeed, the 3.1% higher mortality of triplet- compared to twin-bearing ewes was a key reason for the relatively small differences in overall lamb marking rates reported between triplet- and twin-bearing ewes (176 vs. 160%). The high average mortality of triplet-bearing ewes, together with the high frequency of farms with mortality rates greater than 10%, represents a significant loss of production for individual farms and an animal welfare risk for the sheep industry. Conversely, the 10th percentile for mortality of triplet-bearing ewes was only 1.8%, which indicates there is significant scope to reduce ewe mortality rates if the adoption of pregnancy scanning to identify triple-bearing ewes can be increased, and the components of best-practice management for these ewes can be identified and adopted.
The average survival of triplet-born lambs from the benchmark surveys was reported to be 59%, which was 22% and 33% lower than their twin- and single-born counterparts. The survival of triplet-born lambs was considerably lower than the 68% survival reported across 29 research studies, mostly based in New Zealand, which could reflect, in part, that the data in our study were collected from commercial farms, whereas most of the data reported in Kenyon et al. [
11] were from smaller-scale experiments and research farms. It is known that the survival of multiple-born lambs is lower at a commercial paddock scale compared to an experimental plot scale [
17,
18] or in larger mobs [
6,
7,
8]. Furthermore, most of the studies reported by Kenyon et al. [
11] utilised non-Merino ewes, and it was evident both in our data and Paganoni et al. [
19] that the survival of both twin- and triplet-born Merino lambs was 5–10% lower than their counterparts from non-Merino ewes. The survival of triplet-born lambs varied from 35% to 79% between flocks, which is similar to that reported by Kenyon et al. [
11]. Like ewe mortality, the 90th percentile for the survival of triplet-born lambs demonstrates the scope for improvement, particularly on some farms. Collectively, a survival rate of 70 to 75% for triplet-born lambs would seem to be an achievable target for extensive production systems in Australia where ewes lamb outdoors with minimal supervision. This is especially the case if the knowledge gaps identified by producers in this study can be addressed by further research and used to develop practical management guidelines for triplet-bearing ewes.
One-third of producers surveyed did not identify triplet-bearing ewes, and approximately two-thirds of these producers indicated the main reason for their decision was an insufficient number of triplet-bearing ewes. On average, each of these producers managed nearly 4000 breeding ewes and had they identified triplet-bearing ewes, their actual reproductive rate was likely to be around 153% rather than 148% based on scanning for multiples only. Therefore, it is likely thatapproximately 100 triplet-bearing ewes were mixed with the twin-bearing ewes in these flocks. As only 3% of all ewe flocks in Australia are scanned for triplet-bearing ewes [
9], further work is clearly needed to understand the value proposition for producers to separate triplet- from twin-bearing ewes based on the numbers of ewes mated, current reproductive rates, farm characteristics and management capability. The value proposition will also be influenced significantly by the overall increases in lamb survival and weaning rate that can be achieved from separating triplet- from twin-bearing ewes compared to running all multiple-bearing ewes together. Lamb survival is overestimated in flocks where twin- and triplet-bearing ewes are combined, and in the current study the actual survival in these flocks across all lambs born was likely to be around 78% rather than 80%. In any case, this was still similar to the survival rate achieved by flocks where triplet- and twin-bearing ewes were separated, albeit from an estimated 11% lower reproductive rate. However, it is possible that the lack of difference in survival between flocks that did or did not differentially manage twin- and triplet-bearing ewes is because their differential management may not be optimal. Further research is needed to identify best-practice guidelines for triplet-bearing ewes, including quantifying the potential improvements in lamb survival from separating twin- and triplet-bearing ewes. Benefits could be substantial, especially if management guidelines for triplet-bearing ewes can be developed by addressing the research gaps identified by producers in this study. The non-economic advantages of adopting best practice management guidelines for triplets also need to be considered, including the ethical and emotional impacts of fewer ewe and lamb deaths and satisfaction from achieving greater productivity and profitability.
A mixed-method approach involving more than 200 sheep producers from across southern Australia was effective at establishing the research needs and priorities of producers to improve the survival of triplet-bearing ewes and their lambs. Our hypothesis was therefore supported. The top four priorities for further research identified by producers were to establish targets for ewe condition score, FOO, mob size at lambing and quantify the impacts of supplementation with minerals, regardless of the ewe breed managed. These top four priorities represented between 73 and 81% of all responses, despite variations in the consultative processes used to identify the research priorities. The key research priorities to improve the survival of triplet-bearing ewes and their lambs identified from producer consultation in this study align with the knowledge gaps identified by Kenyon et al. [
11]. Priorities for further work will also be informed by knowledge from the current study of management practices currently adopted by farmers, their production levels and the potential effect of changing a management practice on the mortality of triplet-bearing ewes and their lambs. These priorities will also be weighted based on the ease with which a management change can be achieved within the farming systems and hence the scale of the opportunity to reduce the mortality of triplet-bearing ewes and their lambs.
Most producers indicated the primary reason for managing the condition score of triplet-bearing ewes at lambing was to reduce ewe mortality. On average, the target condition score at lambing for triplet-bearing ewes of 3.3 was similar to that for twin-bearing ewes, but the target varied from 2.8 to 3.5 between producers. To our knowledge, there has been no detailed experimental work relating condition score profile during pregnancy and at lambing to risks of ewe mortality on commercial farms. In contrast to best practice management guidelines for twin-bearing Merino and non-Merino ewes, which require increased feeding to achieve a higher condition score at lambing for most farms [
13,
20,
21], none of the producers involved in the benchmark surveys in our study indicated that low condition score at lambing contributed to mortality of triplet-bearing ewes, whereas almost 50% indicated they tried to prevent ewes from getting over-fat. Concern over multiple-bearing ewes getting too fat appeared to be a bigger issue for producers with non-Merino ewes than Merino ewes and for triplet- than twin-bearing ewes. This was consistent with beliefs that pregnancy toxaemia and ewes being too heavy at lambing were the main causes of mortality of triplet-bearing ewes. It is well recognised that over-fat ewes, especially those with multiple foetuses, are at greater risk of pregnancy toxaemia due to the direct and indirect effects of excessive fat on feed intake [
22,
23]. Optimising the condition score of triplet-bearing ewes will also be influenced by the impacts of condition score on lamb survival, and low birthweight was perceived to be a more dominant cause of mortality of triplet- compared to twin-born lambs by producers in our study. Studies in New Zealand and Australia using non-Merino ewes have found variable effects of ewe condition score at lambing on survival of triplet lambs [
24,
25,
26,
27], but most of these studies were small-plot scale on research stations rather than commercial scale and, in many cases, involved a limited range in condition score. Manipulating ewe condition score at lambing has a greater influence on the survival of twin-born lambs from Merino ewes compared to non-Merino ewes [
17,
27] due in part to lower average birthweights of lambs from Merino ewes [
19], which may indicate a greater positive response of improving condition score in triplet-bearing Merino ewes than for non-Merino ewes. There is a clear need to better define the impacts of condition score at lambing on the mortality of triple-bearing ewes and their lambs at the commercial scale, and it is expected that these responses may differ between ewe breeds.
Producers considered FOO at lambing important to reduce both ewe mortality and especially to improve lamb survival. Whilst the three-fold range in target FOO levels from 800 to 2500 kg DM/ha would, in part, reflect different production environments and time of lambing in relation to seasonal pasture supply, the producers indicated there was a need to better define the FOO targets for optimal survival of triplet-bearing ewes and their lambs. Studies in New Zealand found that offering around 800 kg DM/ha from mid-pregnancy until birth reduced birthweights of triplet-born lambs compared to higher FOO levels [
28], but other studies have indicated that triplet-bearing ewes could be offered a minimum of 800 kg DM/ha without adverse effects on lamb survival provided intake was not restricted during the 2 weeks before lambing [
24,
26]. Another study from New Zealand showed a negative effect of offering triplet-bearing ewes a minimum of 1600 kg DM/ha in late pregnancy compared to 900 kg DM/ha on survival of triplet-born lambs, irrespective of ewe conditions score at mid-pregnancy [
25]. As summarised by Kenyon et al. [
11], literature regarding the effects of ewe nutrition and FOO during late pregnancy and lambing are variable. However, in many cases, studies are limited by low numbers of lambs per treatment, and few have subjected ewes to levels of nutrition well below their theoretical demand, which can occur in environments across southern Australia, especially when lambing in autumn or early winter. There are currently no industry recommendations for the FOO requirements for triplet-bearing ewes during late pregnancy and lambing under commercial farming conditions in Australia. More detailed studies are also needed to better understand the requirement for supplementary feeding triplet-bearing ewes in late pregnancy and lambing, depending on pasture conditions, to reduce ewe mortality and improve lamb survival.
Sheep producers reported that reducing mob size at lambing was a key practice they had adopted to improve the survival of triplet-born lambs, yet this remained a priority for further research. The average mob size at lambing from the benchmark surveys was reported to be 52 triplet-bearing ewes, but it was apparent that producers had very different opinions of the optimum mob sizes, which varied from 10–150 triplet-bearing ewes. Bates et al. [
29] recently reported that mob sizes at lambing varied from 30–200 for triplet-bearing ewes across a small sample of farms, mostly in NSW. Lockwood et al. [
7] reported survey data collected from sheep producers in southeastern Australia, which indicated the survival of single- and twin-born lambs increased by 1.4% and 3.5% when mob size at lambing was reduced by 100 ewes. This was verified by experimental data, which found that reducing mob size at lambing by 100 twin-bearing ewes increased the survival of their lambs by 1.9 to 2.5%, regardless of breed and stocking rate at lambing [
8]. The optimum mob size for twin-bearing ewes was typically less than half that for single-bearing ewes depending on several enterprise-specific factors [
14]. There are currently no recommendations for the optimum mob size during lambing for triplet-bearing ewes [
11]. Mismothering was perceived to be the main cause of death for triplet-born lambs in the current study, and the effects of mob size on lamb survival are likely to be driven by the risk of mismothering. The risk of mismothering is likely to be greater for triplet-born than twin- or single-born lambs, given more triplet lambs will be born per day for the same ewe mob size, triplet-born lambs and their dams have poorer behavioural traits than both singletons and twins [
30,
31,
32], and triplet-bearing ewes have been observed to take longer to deliver their litter than twin- and single-bearing ewes [
33]. More detailed studies to quantify the effects of mob size on lamb survival are needed to underpin economic modelling and determine the optimal mob size for triplet-bearing ewes for specific management settings.
Little is known regarding whether mineral supplementation of lambing ewes can reduce ewe and lamb mortality. Subclinical deficiencies of calcium and magnesium are common in lambing ewes in Australia due to imbalances in pasture grazed by the ewes [
34]. Mineral imbalances in vegetative cereal crops also present a risk of low calcium status in ewes grazing these crops in late pregnancy [
35]. Subclinical deficiencies in calcium and magnesium may increase the risk of dystocia and related issues, including hypothermia in lambs and poor ewe-lamb behaviour [
34]. Providing lambing ewes with ad libitum access to mineral supplements containing magnesium, sodium and calcium has been reported to reduce the risk of ewe mortality when grazing cereal crops [
36]. However, the impact of subclinical mineral deficiencies on lamb mortality and the benefits of mineral supplementation remains unclear. It could be assumed that the benefits of mineral supplementation would be greater for triplet-bearing ewes and their lambs compared to their single- or twin-counterparts, given their higher metabolic demands during pregnancy and lactation.
The sheep producers consulted in this study represented a biased sample, so caution is needed in extrapolating some of the findings across the national sheep flock, especially those relating to levels of reproductive performance. Producers must have utilised pregnancy scanning for litter size to be eligible for inclusion in the benchmarking surveys, and this only represents about 35% of Australian sheep producers [
9]. Furthermore, many producers known to have experience with differential management of triplet-bearing ewes were deliberately targeted. The average reproductive rates for farms that identified triplet-bearing ewes were 150% for Merinos and 172% for non-Merinos, which were significantly higher than the industry average reproductive rates of 122% and 147%, respectively [
9]. The average proportion of triplet-bearing ewes for these farms was over 6%, which is likely to be about double that present across the national flock, but nevertheless, it is still likely that 1 to 1.5 million ewes conceive triplets annually across Australia given that the flock size is approaching 45 million breeding ewes. As all of the producers surveyed had adopted pregnancy scanning for multiples, it is likely that they had also adopted other management strategies to improve reproductive performance compared to the broader population of sheep producers [
5,
6]. Despite higher reproductive rates and, therefore, more multiple-born lambs, the average lamb survival rates for farms in this study were 75% for Merinos and 80% for non-Merinos, which were significantly higher than the industry average lamb survival rates of 69% and 71%, respectively [
9]. Mortality rates of triplet-bearing ewes and their lambs across the sheep industry in Australia are likely to be higher than reported in our study due to survey recall bias associated with self-reported retrospective surveys. Munoz et al. [
37] recently reported that a cohort of 32 farmers from across Victoria in southeastern Australia reported their annual ewe mortality was 2.7% compared to 4.7% based on changes in actual sheep numbers over a calendar year. Furthermore, our data suggest that mortality rates of triplet-born lambs are likely to be higher in flocks where triplet-bearing ewes are mixed with twin-bearing ewes, especially when none of the ewes are pregnancy scanned. It is clear that changes in profitability from improving the survival of triplet-bearing ewes and their lambs will be relatively small for most farms where triplet-bearing ewes represent less than 5% of the ewe flock. The increasing prevalence of triplet-bearing ewes, however, means that identifying and adopting best-practice management of triplet-bearing ewes and their lambs will be important for improved productivity and to ensure animal welfare is optimised to meet consumer demands for ethical product.