Ovine Observer

Reproductive wastage in young ewes

Tom Clune, Amy Lockwood, Serina Hancock, Sue Beetson, Andrew Thompson & Caroline Jacobson, Murdoch University, Murdoch, WA
Author correspondence: t.clune@murdoch.edu.au
This research is funded by Meat and Livestock Australia. DPIRD Sheep Industry Business Initiative has provided support through scholarships awarded to PhD students involved with the project.

This article presents the preliminary findings of an ongoing, national project investigating the magnitude, timing and causes of reproductive wastage for maiden ewes.

Introduction

Understanding when and why lambs are lost (‘wastage’) between conception and weaning is important for developing strategies to improve sheep reproductive performance.  The role of wastage during pregnancy (loss of foetuses between scanning and lambing) as a contributor to poorer reproductive success in maiden ewes is not well studied.

Overall wastage can be determined by measuring the number of foetuses present at scanning and number of lambs marked or weaned, but this doesn’t distinguish losses that occur during pregnancy (abortion) from losses during and after birth (lamb survival). Studies show that most lamb deaths occur in the first three days after birth, but these have been conducted largely with adult ewes.

The number of lambs born can be assessed by conducting lambing rounds. Farmers have been reporting unexplained discrepancies between the number of lambs at scanning and birth, suggesting more losses are occurring in pregnancy than would normally be expected. These discrepancies are more commonly reported for maiden ewes, and especially for maiden ewe lambs joined at 8-10 months of age. It is not clear if these discrepancies represent errors at pregnancy scanning, wastage during pregnancy (abortion), errors recording the number of lambs born or a combination of these factors.  Overseas studies suggest that foetal losses during mid- to late-pregnancy may be an important source of wastage in young ewes. If this is the case for Australian sheep, wastage during pregnancy (abortion) could explain discrepancies between the number of lambs scanned and number of lambs born as reported by farmers.

Methods

Approximately 200 ewes at each site were monitored from joining until lamb marking on four farms in the south west of Western Australia as part of a larger national project being conducted 2018-2020. Two of the farms joined maiden Merino hoggets (18-20 months at joining) and two farms joined maternal composites as ewe lambs (7-9 months at joining).

Weight, condition score and blood samples were collected from ewes at five time points between pre-joining and marking, and pregnancy scanning was conducted twice to determine foetal number and viability. Scan 1 was conducted 76-88 days from the start of joining and scan 2 was conducted at 116-119 days from the start of joining.

Ewes and lambs were monitored daily over the lambing period. Lambs were tagged, recorded as live or dead and their dam was identified. Lamb survival per ewe was assessed to marking. Ewe udders were assessed to determine lactation status (wet or dry) at marking. Lambs that were dead at lambing rounds (died between birth and tagging) were categorised as ‘born’, and counted as wastage in birth-marking period (i.e. born but did not survive to marking).

Producers collected any aborted tissues and lambs that died within 24 hours of birth for post-mortem exam. In most cases, dead lambs collected by farmers were frozen for storage prior to conducting a post mortem. This impacted accurate interpretation of necropsy findings, however attempts were made to categorise the cause of death based on gross (visual) findings.

Results

Results summary

• Lamb losses during pregnancy varied between farms and age groups
• For maiden ewes joined at 18-20 months old, the majority of wastage occurred between birth and marking
• For maiden ewes joined at 7-10 months old, about half of  wastage occurred between scanning and birth
• For ewe lambs, wastage can occur in pregnancy without obvious signs of an abortion outbreak.

Timing of wastage

The timing of wastage is shown in Table 3. More wastage occurred in the period from birth to marking compared to wastage during pregnancy (scan 1 – birth) for three of the four farms.

Maternal ewe lambs had greater wastage during pregnancy compared to Merino hoggets (p<0.001). For ewe lambs, 49% and 41% total loss between scanning-marking occurred during pregnancy (between scan 1 and birth).Importantly, wastage between scan 1 and birth occurred without visual evidence of an abortion storm, with only one aborted foetus and one ewe with retained foetal membranes noted at one farm.

Wastage during pregnancy (abortion) between scan 1 and scan 2 was evident in both maternal ewe lamb flocks (12/148 ewes at Farm 3 and 2/129 ewes at Farm 4) but not at either farm with Merino hoggets.  Wastage between scan 1 and scan 2 was higher at Farm 3 than other farms.

¹ Number foetuses scanned / number of ewes joined
² Number of lambs marked / number of ewes joined
³ % foetuses (or lambs) lost from start to end of respective period. Lambs dead at birth (full term) are included in birth – marking wastage
^abc Wastage values (% foetuses) in rows with different superscripts are significantly different (two-tailed p<0.05)

Causes of perinatal wastage

A total of 135 post-mortem examinations were performed. This represented 135/237 (57%) foetal or lamb mortalities between scan 2 and marking. Cause of death category was established for 70% cases. The main cause of death varied between farms but overall most lambs died from stillbirth, dystocia and starvation-mismothering-exposure complex (Figure 3).

Figure 3 Overall cause of death category for foetus/lambs submitted for gross post-mortem examination

Discussion

The key finding from the preliminary data from this study is that foetal loss between scanning and birth is an important contributor to reproductive wastage in some flocks of maiden ewes, even without obvious signs of abortion that could alert the producer to a problem in the flock. Wastage during pregnancy was higher for ewe lambs compared with hoggets.

Wastage during pregnancy is challenging to detect for typical Australian sheep production systems, and can easily go undetected. Monitoring of ewes in this study was what would be considered typical or greater than standard management, and aborted tissues were recovered for only two ewes. Most farms do not record number of lambs born, so would not be aware of discrepancies between number of lambs scanned and number of lambs born.

Differences between the number of lambs scanned and the number of lambs identified at birth could represent either scanning errors, abortion, or birth of lambs that died soon after birth and were not found during lambing rounds. In this study, scanning errors were unlikely to be an important contributor to wastage because ewes were scanned twice by experienced scanners. It is likely that some of the apparent wastage between scanning and birth included failure to find lambs that were born and died soon after birth.

This highlights the challenges with identifying timing of reproductive wastage, even when lambing rounds are regularly performed by experienced managers. It is possible that poorer maternal instincts of maiden ewes may contribute to difficulties in matching weak or dead lambs to their dams or to recover dead lambs, as inexperienced ewes may be less likely to show interest in the lamb.

It is likely that abortion, rather than simply failure to find dead lambs during the lambing rounds was an important contributor to wastage between scan 2 and birth for Farm 3. At this farm, 8% of ewes had evidence of abortion between scan 1 and scan 2, and a ewe that had a viable foetus at scan 2 was found with evidence of retained lambing membranes at the pre-lambing sampling confirming abortion was occurring on this farm. However, both cases were likely to have been missed with typical monitoring.

Lamb losses between birth and marking represented the largest source of reproductive wastage. This is consistent with previous studies using mature ewes. The causes of lamb deaths based on post-mortem examinations were consistent with other Australian studies that showed dystocia (difficult birth) and the starvation-mismothering-exposure complex were the most common causes of perinatal death. Stillbirths were an important source of wastage for Farm 3, and work is ongoing to identify possible causes.

Recommendations based on preliminary data

• Based on preliminary findings, providing ‘extra care’ to maiden ewes could reduce overall wastage by reducing lamb losses between birth and marking. Appropriate lambing paddock selection, lambing mob size and feeding management can contribute to improved lamb survival. More information on managing ewes to improve lamb survival is available on the managing pregnancy in ewes webpage.

• Ewe nutrition and lamb birth weight is a major factor for lamb survival. Managing maiden ewes to reach body condition score targets during pregnancy and lactation has been shown to improve lamb survival. More information on ewe nutrition in late pregnancy is available on the lambing and lactation webpage.

• Reproductive wastage can occur in pregnancy, even without obvious signs of widespread disease. Ewes that abort lambs may not appear sick. Aborted lambs are easily missed and affected ewes are likely to go unnoticed. Producers should seek veterinary advice if they suspect abortions in ewes or observe an unusual number of premature, stillborn or weak lambs. Advice should be sought as soon as possible so that useful samples can be collected. Delaying sampling or collecting the wrong samples can jeopardise investigations.

Opportunities for participation

This study is being expanded to a total of 30 farms across a wider area (WA, SA and Vic) in 2019-2020. Data from expanded fieldwork and survey will establish variability for reproductive wastage across a range of production systems and environments.  Producers that are joining at least 200 maiden ewes, can perform lambing rounds and are interested in identifying opportunities to reduce wastage are encouraged to contact Tom Clune via email (t.clune@murdoch.edu.au) for more information on becoming a participant in the project.

If producers or veterinarians find cases of abortion, premature births or still births, they are encouraged to submit samples under the ovine abortion surveillance scheme run by DPIRD.  The scheme supports disease investigation of aborted or dead newborn lambs free of charge. Samples are tested for infectious causes of abortion known to occur in Australia as well as those that are exotic to Australia. If results identify an infectious disease is causing the losses, management strategies to reduce future impact may be available. Samples or whole, fresh or frozen carcasses, can be submitted to your local DPIRD veterinary office or private veterinarian. For further information about the abortion surveillance scheme, producers can visit the DPIRD website, or contact Dr Anna Erickson Anna.Erickson@dpird.wa.gov.au or +61 (0)8 9881 0211.

Producers interested in understanding reproductive performance of their sheep are encouraged to participate in the national maiden reproductive wastage survey. This will provide data to help benchmark performance of ewe lambs and maiden hoggets across a range of production environments. Producers can contact Elise Bowen for more information (elisejbowen@gmail.com).