Reducing foetal and lamb losses in young ewes| 2023

Summary

Improving reproductive performance for maiden ewes is a priority for the Australian sheep industry. This project has determined the extent, timing and causes of lamb mortality between scanning and marking in maiden ewes, including the contribution of losses between scanning and birth (abortion).

Objectives

This project addressed four research questions:
1. Is foetal loss a significant contributor to overall reproductive wastage from young ewes between scanning (day 42 pregnancy) and marking, and if so, when are losses occurring?
2. What is the background prevalence in young ewes for infectious diseases that have potential to cause abortion?
3. Is exposure to infectious disease associated with foetal loss in young ewes, and if so, how what is the relationship between the timing of exposure and outcome for pregnancy?
4. Can management strategies reduce the risk foetal loss between day 42 and lambing, and increase overall marking rates from young ewes?

Key findings

Survey results indicated both a lower reproductive rate and lower survival contribute to lower marking rates in maiden ewes compared to mature ewes.

Where an abortion or stillbirth diagnosis was made, infectious diseases were implicated with 81% of abortion and stillbirth investigations. The three most common infections (Campylobacter spp., Listeria spp. and Toxoplasma gondii) accounted for 86% investigations with a diagnosis.

Lamb mortality from birth to marking represented the greatest contributor to foetal and lamb mortality after scanning, but mid-pregnancy abortion was an important contributor to lamb mortality in some ewe lamb flocks.
Lamb necropsies identified starvation-mismothering-exposure, dystocia and stillbirth as the most common causes of perinatal lamb death. Chlamydia pecorum is an emerging cause of reproductive disease in sheep. It is unlikely that this is a new condition but rather the use of improved molecular diagnostic tests for exotic disease exclusion testing have allowed laboratories to detect C. pecorum.

Benefits to industry

This project provided insights on the reproductive performance of maiden ewes, and offered new insight into the contribution of in utero foetal loss and perinatal lamb mortality to the reproductive performance of maiden ewes.
The findings will be made available to existing networks to ensure the learnings are incorporated into existing programs and learning resources to be distributed as widely as possible. The participatory research approach allowed producers to gain new insight into sources of reproductive losses in their maiden ewes and diseases impacting ewes on their farm. The input and feedback from host producers has been incorporated into recommendations and protocols for investigation of poor reproductive performance to ensure that these are both practical and effective.

Future research

Future research should include the expansion of maiden ewe reproductive performance datasets to provide robust benchmarks for maiden ewe reproductive rate, lamb survival and marking rates across major sheep production zones. Furthermore, in response to considerable variation between flocks, investigation of multifactorial nature of abortion across major sheep production zones is needed to inform cost-benefit analyses for interventions to address lamb survival. Finally, further research should aim to fill remaining gaps in the understanding of the epidemiology of C. pecorum.