Report re Report Title

AGRICULTURE FLAGSHIP

R&D priorities and opportunities for lamb survival Report of planning workshop held at CSIRO Chiswick, 15-16 January 2015 Sabine Schmoelzl, CSIRO Alison Small, CSIRO Alan Bell, Cornell University, Ithaca, NY

Enquiries should be addressed to: Dr Sabine Schmoelzl CSIRO Agriculture Flagship Livestock Phenomics T: 02 6776 1331 M: 0420 280 137 Postal Address: New England Highway, Armidale NSW 2350

Dr Alison Small CSIRO Agriculture Flagship Animal Health and Welfare T: 02 6776 1435 M: 0420 280 137 Postal Address: New England Highway, Armidale NSW 2350

Citation Schmoelzl S, Small AH and Bell AW (2015) R&D priorities and opportunities for lamb survival – workshop report. CSIRO, Australia.

Copyright and disclaimer © 2015 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO.

Important disclaimer CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.

Foreword

The Chiswick Lamb Survival Workshop was attended by representatives from the Animal Genetics and Breeding Unit (AGBU), University of New England (UNE), Charles Sturt University (CSU), University of Western Australia (UWA), University of Adelaide (UA), Department of Agriculture and Fisheries Western Australia (DAFWA), New South Wales Department of Primary Industries (NSW DPI), Commonwealth Scientific and Industrial Research Organisation (CSIRO), AgAchieve, Australian Wool Innovation (AWI) and Meat & Livestock Australia (MLA). Three groups, with representation from NSW DPI, UNE, CSU, University of Central Queensland (UCQ), UNE and CSIRO, had previously submitted pre-proposals to MLA for consideration in the inaugural call for Rural R&D for Profit (RRDfP) funding by the Australian Government. The groups had been encouraged by MLA to build a collaborative joint proposal for submission in a subsequent RRDfP funding round. The aim of the workshop was to bring representatives of these groups together, with addition of other RD&E groups active in the area of lamb survival, and to discuss future avenues for collaborative research. Specific objectives were:    

To review current state of research in the area of lamb survival To identify opportunities for collaborative research in the area of lamb survival, in particular following recent call for proposals for Rural R&D for Profit To identify gaps and opportunities for new/additional research To identify research priorities for lamb survival

Professor Emeritus Alan Bell of Cornell University generously offered his time to moderate the workshop, and to edit this report. We owe him great thanks.

R&D priorities and opportunities for lamb survival | i

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Contents

Foreword ........................................................................................................................................................i Acknowledgments ......................................................................................................................................... v Executive summary...................................................................................................................................... vii 1

Introduction .................................................................................................................................... 8

2

Workshop proceedings ................................................................................................................... 9 2.1 Past and current research on lamb survival ......................................................................... 9 2.2 Knowledge gaps and opportunities for new/additional research ...................................... 10 2.3 Proposals for future research ............................................................................................. 13 2.4 Further research opportunities for lamb survival............................................................... 16 2.5 R&D priorities for lamb survival .......................................................................................... 21

3

Recommendations ........................................................................................................................ 22 3.1 Research recommendations ............................................................................................... 22 3.2 RD&E outcomes .................................................................................................................. 23

Appendix A

Workshop program............................................................................................................. 24

Appendix B

Workshop attendees .......................................................................................................... 25

References .................................................................................................................................................. 26

R&D priorities and opportunities for lamb survival | iii

Figures Figure 1: Representation of underlying factors and impacts of dystocia on lamb survival ....................... 11 Figure 2: NMR metabolic profile analysis in lambs at 0, 4, 8 and 12 hours after birth .............................. 14 Figure 3: Ewe-lamb interactions ................................................................................................................. 18 Figure 4: Economic values for reproduction traits Left graph: Relative economic values (REV; in $/ewe) for reproduction traits as function of Mean flock size. Right graph: Proportion of litter size categories as function of mean litter size. ....................................................................................................................... 20 Figure 5: Conceptual diagram of value proposition ................................................................................... 21

Tables Table 1: Causes of lamb mortality ................................................................................................................ 9 Table 2: Underlying factors leading to lamb mortality ............................................................................... 10 Table 3: Contact duration between ewes and each of their offspring for the two 24h periods after lambing (from Broster et al 2010) .............................................................................................................. 15

iv

Acknowledgments

Funding support from CSIRO Agriculture Flagship for the venue and workshop costs is gratefully acknowledged, as are the contributions of the participants and their organisations. The participants displayed a genuine collegiality towards developing a plan to help address this most important of production and welfare issues for the Australian sheep industry.

R&D priorities and opportunities for lamb survival | v

vi

Executive summary

Lamb survival is a research, development and extension (RD&E) priority of high national importance. This is because newborn lamb losses in the Australian sheep industry are high and significantly impact on reproduction rates and profitability, and because they are a major animal welfare concern with potentially high impact on consumer perceptions and market access for the Australian sheep industry. Most lamb losses occur in the first 48 h of postnatal life, with the majority attributed to the dystociamismothering-starvation/exposure complex (DMS). Predation can be important on individual properties but is much less so compared to DMS. Factors influencing DMS include ewe and lamb physical characteristics, litter size, and management factors such as nutrition of the ewe, shelter, mob size and stocking density. Significant differences in weaning rates within and between sheep breeds demonstrate the importance of genetics even though heritability of survival to weaning is estimated to be low. The development of more specific component traits affecting lamb survival is likely to improve heritability estimates. However, management decisions and genetics contribute to lamb survival and should therefore be studied in an integrated context. A priority area identified for research is the establishment of better phenotypes associated with lamb survival. Improved measurements of maternal physical characteristics that contribute to dystocia, and of factors affecting maternal and lamb behaviour and physiology, will lead to better understanding of the relative contributions of management interventions and of traits for genetic selection. This information will help to improve guidelines for management and feed into genetic selection programs including development of genomic predictions. A second priority area is the development of mechanisms for integration of RD&E. Such mechanisms should include collection of high quality industry data to inform research. They should also aim to support more extensive uptake of management and genetic selection recommendations by producers in a timelier manner through improved methods of communication for new research results. Better integration of management related and genetic RD&E is needed to allow improvements in this historically complex field of research which has had only moderate success in improving lamb survival rates across the Australian sheep industry. Recent technological advances, including those that enable more rapid collection and use of large data sets to develop practical applications, will allow this important issue for the Australian sheep industry to be better addressed.

R&D priorities and opportunities for lamb survival | vii

1

Introduction

Reproductive wastage in the sheep industry, and in particular production losses due to lamb mortality up to weaning has been estimated to be around 30% when pregnancy rates according to pregnancy scanning are compared with weaning rates. Despite ongoing selection for reproductive success by many sheep producers, survival rates have only incrementally changed over decades (Trompf 2012), and even under optimised management conditions survival rates typically reach only 85 to 90% in singles and 65% in twins (Copping & Hocking Edwards 2006; Edwards et al. 2011). Genetic and epigenetic factors affecting lamb survival have been reviewed by Brien et al. (2014), and lamb survival in Australian flocks has been comprehensively reviewed by Hinch and Brien (2014). Increased twin survival, rather than increased twinning rates, is considered to be one of the most effective changes that would benefit the Australian sheep industry, while the reverse, higher twinning rates at current twin loss rates would be less advantageous economically and less socially acceptable (Arnot 2012). In a 2006 MLA report, the annual economic impact of increasing lamb survival by 10% was estimated to be $56M, while the cost of peri-natal mortality in pastoral zones alone was estimated $26M per annum (Sackett et al. 2006). An average loss of 17% in singles and 32% for twins from the date of pregnancy scanning to weaning in Merino and crossbred ewes was reported by Fowler (2007). Furthermore, provision of shelter, with the benefit of a 25% reduction of mortality of twin lambs within a self-replacing Merino wool flock with 30% twin pregnancy rate, was estimated to be between $1.25 and $2.55/ewe, depending on the twin mortality rate without shelter (Young et al. 2014a). Critical control points for increasing reproductive performance can be used to inform research, and increased survival of twins has been highlighted as the component of reproductive performance with the highest potential for economic gains (Young et al. 2014b). Factors affecting lamb survival include dystocia, mismothering/starvation, exposure and predation were recently reviewed by Hinch and Brien (2014), and economic effects of good ewe management as shown by the LifetimeWool project have been summarised by Oldham et al. (2011). About two thirds of lamb losses occur within the first 72 hours of birth (Alexander et al. 1955; Brien et al. 2009). Dystocia and Starvation/Mismothering/Exposure (SME) are the main reasons for perinatal death (Nowak & Poindron 2006) and careful management of body condition score is a crucial management component in reducing lamb losses (Kenyon et al. 2011; Kenyon et al. 2012; Roche et al. 2013). The Chiswick Lamb Survival Workshop specifically addressed the problem of on-farm mortality in lambs, although similar issues exist for calf mortality, particularly in the extensive systems of Northern Australia. For the purposes of the workshop, an overview of the current state of research on lamb survival was invited, followed by a discussion on main areas of importance for lamb survival. The three pre-proposals previously submitted to MLA for consideration for submission to the Rural R&D for Profit funding call from the Commonwealth Department of Agriculture were then presented. During the second day of the workshop, additional presentations examined additional and complimentary areas of research and development warranting attention. These included links between feed efficiency and ewe reproduction, ewe supplementation with micronutrients during pregnancy, maternal and lamb behaviour, and the incorporation of lamb survival traits in selection indices. Finally, a set of recommendations was developed as priority areas for research.

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2

Workshop proceedings

In preparing for the workshop, presenters were encouraged to use an interactive and informal presentation style, and frequent questions and discussion during presentations were explicitly encouraged. This led to lively and productive sessions, in which the presented and discussed content frequently merged. The following section provides brief summaries of session topics including outcomes of discussion. Feedback and comments on a draft version of the report were sought from all participants and have been incorporated in the following proceedings.

2.1

Past and current research on lamb survival

Geoff Hinch gave an overview of past and current research on lamb survival. Lamb survival is both a production issue and an animal welfare issue. There is also the added risk of public perception which could have large negative effects similar in scale to the live export debate. Around 80% of lamb losses to weaning occur in the first 48 hours after birth. Current lamb production data suggest that average weaning percentage is around 87% (lambs weaned per ewe). Lamb mortality is around 25% (Sheep CRC Information Nucleus Flock (INF) data: 21% in Merinos; 15% in crossbreds). Data from NZ (2000) suggests average weaning percentage of 121%; and mortality of 11% should be achievable. Best targets as proposed by LifetimeWool are 90% survival for single and 70% for twin lambing Merino ewes. Data from the Information Nucleus Flock of the Sheep CRC showed that dystocia is a large problem, and in combination with starvation/mismothering accounts for the majority of lamb deaths (47% and 25% respectively) (Geenty et al. 2014). In comparison, earlier results from the Sentinel Flock in Victoria attributed 21% to dystocia and 45% to starvation/mismothering; however, the total deaths attributable to these two factors in the two data sets are virtually equivalent. A discussion followed on the differentiation between Dystocia and Starvation/Mismothering, and there seemed to be a consensus that the issue is a continuum, with a large part of starvation/mismothering at least theoretically attributable to brain damage sustained during parturition. Table 1: Causes of lamb mortality CAUSE OF DEATH

INF DATA

SENTINEL FLOCK (VIC)

Dystocia

47% (total)

31% (likely does not include Dys3)

Dys1

8.8%

Dys2

20.6%

Dys3 (incl. starvation)

18%

Starvation/Mismothering

25%

45% (likely does include Dys3)

Predation

6.7% (certain properties contribute most significantly)

4%

Premature/dead in utero

10.6%

11%

Exposure

5.6% (specific climatic events contribute most significantly)

8%

Infection

0.6%

5%

R&D priorities and opportunities for lamb survival | 9

Table 2: Underlying factors leading to lamb mortality MATERNAL

NEONATE

CONTRIBUTING FACTORS

Behaviour

Behaviour

Breed

Starvation

Starvation

Predation Colostrum Onset

Parity Thermoregulation Exposure

Nutrition

Starvation Size/Fitness Difficult Birth Infection/Disease

Size/Fitness

Environment

Difficult Birth Infection/Disease

Litter size

Premature birth and death in utero respectively accounted for 10% and 11% of lamb deaths, and followed the dystocia/starvation/mismothering complex in magnitude. Predation in research flocks accounted for a comparatively small percentage with 6.7% and 4%, respectively for the two studies, with most of the 6.7% of the INF data attributable to one or two specific localities. Overall, predation was seen as mainly opportunistic by workshop participants, with localized events warranting targeting of predators. In the two quoted studies, exposure accounted for 5.6% and 8% of lamb deaths, which was a surprising result in comparison to common assumptions. The comparatively low percentage of deaths directly attributable to exposure could potentially be a cause for the lack of reduction in lamb losses experienced by producers after erection of lambing shelters. Infection was the least significant contributor to lamb losses, representing 0.6% and 5%.

2.2

Knowledge gaps and opportunities for new/additional research

A wide range of contributing factors to lamb losses were discussed throughout the workshop. A need for better understanding was identified in the following areas:

2.2.1 ADOPTION RATES Adoption rates among producers are highly variable, and low in some segments of the industry. Variability in lamb loss rate is high, and return on investment to reduce lamb losses may take time to be realised. Small groups of producers can work well as motivation increases with friendly competition. Lamb loss is seen as a loss in potential income and as such is difficult to quantify, predict and visualise, which could be a barrier to adoption. Research in the area does not always reach the producer, and isn’t always readily accessible to industry consultants. Regionally, a comparatively high rate of uptake may have been achieved, and therefore additional gains may be slower to be realised.

2.2.2 DYSTOCIA Dystocia/starvation/mismothering complex (DSM) is of paramount importance in lamb losses. The relative contribution of dystocia (as in prolonged parturition event leading to cerebral hypoxia) is uncertain, probably due to diagnostic limitations. Factors contributing to dystocia are excessive body condition score (BCS) of the ewe; unfavourable pelvic dimensions; heavy lambs; large framed lambs; weak uterine tone and 10

a resulting lack in force of contractions; and insufficient amniotic fluid production. Management decisions as well as genetic selection would benefit from understanding this complex better. Pregnancy is a key time to set up lambs and ewes for perinatal success. Better phenotypic characterization of dystocia is important and required.

Figure 1: Representation of underlying factors and impacts of dystocia on lamb survival

2.2.3 NUTRITION AND MANAGEMENT Prenatal nutrition is understood to be a contributor to lamb losses, and recommendations are for ewes to be managed to BCS 3. At the same time it was acknowledged that some animals manage well on lower BCS but the reasons are not well understood. Micronutrient levels are recognized to be important for lamb development; the relevance of risk factors such as application of fertilisers, pastures of high clover content, or grazing of cereals, tends to be underappreciated in the industry and in extension guidelines as there is little recent research in the area. Shelter provision has been investigated previously. Return on investment seems to vary greatly between properties, and may not be realised for a number of years even where relevant. Ewes and lambs may have to learn to use the shelter over time and hence levels of cognition and learning might factor in the success of shelter provision. Furthermore, climatic events are unpredictable in any given year, leading to uncertain return on investment in the short term. Shearing time in relation to birthing varies greatly between regions and properties. Some studies have looked at effects of shearing on birth weight, with varying results.

2.2.4 GENETIC SELECTION Selection for lamb survival is mostly indirect through the trait Numbers of Lambs Weaned (NLW) which does lead to higher twinning rates. If producers fail to recognize the relevance of improved management

R&D priorities and opportunities for lamb survival | 11

for twin bearing ewes, the lamb loss rate can still be high. In this case, production might increase but the risk of negative public perception is not addressed. Best phenotypic indicators in the INFs were rectal temperature; maternal behaviour score, and lamb vigour score. However, the heritability of these traits is low, and the phenotypic correlations are very low or absent. There could be a trade-off between selection for muscling and fat deposition, including brown fat depots. From a genetic perspective, it is imperative to measure as closely as possible the trait that should be improved, rather than proxies. For lamb survival, it would be therefore important to record rearing ability, including multiple-rearing ability. Lamb survival is by definition a composite trait. Better genetic gains might be made if component traits were available. Of high importance are better quality of data and pedigree data from industry. There might be more willingness by producers to pay for a service (such as pregnancy scanning) rather than adding to the workload. Remote technologies and also DNA based technology may well have advantages here. Genomic selection might present an opportunity as the technology has developed rapidly in recent times, and costs have reduced. Lamb survival as a composite trait would not be ideally suited to genomic selection, and research in New Zealand supports this notion. If a physiological marker for lamb vigour could be identified, this might be more promising as genomic prediction for physiological parameters is more successful.

2.2.5 MATERNAL BEHAVIOUR Current measures for maternal behaviour show a poor relationship with lamb survival. Ewe temperament is not a good proxy for mothering ability. Temperament is a difficult to define trait. Human presence impacts on the expression of behaviour, hence remote monitoring may well be more valuable than direct assessment by humans. Personality/temperament has a functional linkage to metabolism. In sheep this has not been explored but could provide a basis for temperament selection and/or better understanding of the impact on management decisions on maternal behaviour. Lamb behaviours have been investigated more than maternal behaviours but separation of both might be misleading as there is a tight interaction between the two. Acoustic analysis of vocalisation patterns suggests that correct cues are necessary to establish a ewe-lamb bond. Detailed understanding of maternal and lamb behaviour would be beneficial to identify on-farm strategies to improve maternal investment and ewe-lamb bonding leading to improved lamb survival.

2.2.6 PHYSIOLOGY There is some research activity in this area within PhD student projects, with a focus on thermoregulation. Thermoregulation contributes to cold tolerance and is seen as one of several components enabling the lamb to stand, suckle and follow the ewe, or more generally contribute to lamb vigour. It is important to better understand the relationship between metabolic rate and activity and success to suckle and follow the ewe. Some candidate markers exist (blood urea; fructose/glucose ratio). In addition there are new technologies that allow metabolome-wide analysis which greatly increase the power to detect associations.

2.2.7 EWE HEALTH Relative contributions to reproductive success of issues such as retained foetal membranes, post-partum infections, metabolic and micronutrient imbalances, and tendency to prolapse (pre- and postpartum) are poorly understood.

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2.3

Proposals for future research

2.3.1 BEYOND 100% WEANING – OPTIMIZING THE SURVIVAL AND PRODUCTIVITY OF YOUNG SHEEP (SUE HATCHER) Producer groups formed around contractors and scanners could be utilised to both more effectively disseminate information on lamb survival and collect relevant on-farm data on a range of measures of reproductive success which are currently not captured. This will allow better understanding of regional differences, as well as impact of management decisions such as pasture management, mob size, nutrition, and health. The aim of the project is to achieve a 10-15% increase in net reproduction rate in commercial sheep flocks. The three key components of the integrated R&D program are: facilitation of the development of the sheep pregnancy scanning industry in Australia; development of both regional and seasonally specific management guidelines for young sheep; and targeted research to support regional management guidelines for young sheep.

Scanning industry development    

Approximately 30% of breeding ewes scanned by 110 scanners Scanning industry is growing - new entrants & growth of existing client base (~10%) One-to-one contact with sheep producers at key times (effective conduit of information, increasingly important) Development of a web based system to capture, store, analyse & report scanning information (benchmark client performance, track industry development, regional trends in sheep production)

Development of management guidelines The guidelines developed should be regionally and seasonally specific, and targeted at young sheep. Case study sites in ‘challenging’ environments (high rainfall and sheep cereal production zones) will provide a focal point for facilitated ‘Beyond 100% clubs’, aiming to achieve 100% or greater NRR, and serve to collect relevant industry information from case study sites.

Targeted research 



Developing regionally specific management protocols (nutritional and animal health guidelines; optimal supplement ratios; positive post-weaning growth rates; survival, wool production and quality; early reproductive success) Range of production scenarios

Targeted research supporting guidelines Regionally specific management protocols (nutritional and animal health guidelines; optimal supplementation; positive post-weaning growth rates; survival, wool production and quality; early reproductive success) will be developed for a range of production scenarios. Herbage quality and characteristics, frequency of imprint feeding, paddock vs yard weaning, feedlotting or targeted production feeding and other factors will be taken into account. The work should link with GrassGro modelling of seasonal, production and market-based factors. Benefits of this work would flow to producers and researchers through close connection, thereby improving the ability to tailor applied research to the needs of the producer. Integration with more strategic research would be a valuable tool to ensure it targets areas of greatest impact. In discussions it was pointed out that it would be useful if the data could easily integrate with SheepGenetics, and if the producer groups align with the LifetimeWool program.

R&D priorities and opportunities for lamb survival | 13

2.3.2 AN INTEGRATED APPROACH TO REDUCE LAMB MORTALITY RATES (SABINE SCHMOELZL) Ewes and lambs should be studied as a unit. For twin-bearing ewes, nutrition is more important. Characterisation of the metabolic state of ewes and lambs under optimal or restricted nutrition is an opportunity to find phenotypic markers for lamb vigour based on physiology. This is closer to the parturition event which is the time of greatest risk of lamb loss, and could therefore be more informative than focus on success to weaning, which is even more influenced by the environment. Phenotyping should include  

Physiological measurements (body weight, frame measurements, thermogenic capacity, body temperature, blood glucose and metabolomic analysis) and Behavioural measurements including established measurements such as latency to bleat, and novel measurements such as movement logging to provide agitation scores for ewes and activity scores for lambs.

A small-scale pilot study showed that metabolite profiles could discriminate between time of birth at 0, 4, 8 and 12 hours after parturition (Fig 2). Phenotypic characterisation of lamb vigour would be useful for understanding the effects of management practices such as supplementation, and also for genetic selection, including the development of genomic tools. As a first step, this would require controlled experimentation for deep phenotyping, followed by a larger scale experiment on resource flock populations for validation. A possibility that was discussed was the study of extreme phenotypes if mothers which were repeatedly unsuccessful at rearing lambs could be identified, and contrasted with successful twin-rearing ewes. Low and high vigour rams have been selected for phenotypic studies in previous PhD projects. Repeatability is an important issue to consider. Twin-rearing ability is a trait distinct from single-rearing ability.

Figure 2: NMR metabolic profile analysis in lambs at 0, 4, 8 and 12 hours after birth

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2.3.3 ENHANCING CALF AND LAMB SURVIVAL THROUGH BETTER MEASURES OF MATERNAL INVESTMENT (MARK TROTTER) This area constitutes a knowledge gap in both sheep and cattle. Maternal investment including maternal behaviour is important for maternal-offspring interaction and bonding, and influences offspring survival. Of particular interest is maternal investment and its relationship with post-partum losses and the trade-offs between investment in current offspring and capacity to re-breed. The latter is of particular importance to the cattle industry but all factors have implications across the sheep and cattle industries, providing a framework for cattle and sheep producers to account for direct and indirect effects of maternal variance, and to identify opportunities for management changes affecting lamb and calf survival. Autonomous and real-time livestock monitoring offer opportunities to remotely monitor and record livestock behaviour. Ewe movement and ewe-lamb contact measured by proximity loggers are influenced by shelter type, birth number and stocking rates (Table 3) (Broster et al. 2010). Maternal variance components of cow-calf contacts have previously been estimated. The measurements of cow-calf interactions and social networks as an indicator of maternal investment can be used for genetic selection and for selection of management strategies and decisions for faster gain. The objectives are to:    



Identify the impact of parturition location on lamb and calf survival and whether management factors influence losses; Quantify if mother-offspring proximity relates to calf and lamb performance and determine whether the spatial relationship can be used as a proxy for mothering ability; Validate whether commercial systems (e.g. Taggle systems) can be used to identify maternal parentage; Determine whether mother or offspring movement (or lack of) can be used as an early warning to identify post-partum losses and propose management intervention strategies that will reduce losses; Provide quantitative measures of mothering to inform overall EBVs, either directly as a trait or indirectly to account for maternal variance.

Table 3: Contact duration between ewes and each of their offspring for the two 24h periods after lambing (from Broster et al 2010) TREATMENT

PERIOD, H (S.E.M.) C

D

MEAN

Single-H (n=8)

12.91 (1.038)

9.14 (1.271)

11.02b

Twin-H (n=20-C, 12-D)

08.65 (1.027)

7.97 (0.655)

08.31a

Twin-S (n=20-C, 12-D)

11.54 (0.842)

8.57 (0.586)

10.05b

Mean

11.032

8.561

Single-H = Hessian rows with single bearing ewes; Twin-H = Hessian rows with twin bearing ewes; Twin-S = shrub belts with twin bearing ewes. C – 24-h post-lambing and D – minimum 3 days post-lambing. a,b Means

within a column with different letters differ at P