Improving the reproductive performance of sheep is a national research priority, but identifying which components of the reproductive process should be the highest priority for further research is complex. This analysis determined the potential benefit to industry from increasing conception, survival of single- or twin-born lambs, survival of ewes at lambing, weaner survival and early reproductive success. Increasing the survival of twin-born lambs was the area with the highest pay-off, whereas increasing weaner survival had the lowest pay-off.

A large source of reproductive wastage in the Australian sheep flock has traditionally been lamb loss at birth or in the neonatal period. This review examines the history of reported losses throughout Australia and the latest evidence for levels of lamb survival now that pregnancy scanning technologies are available. The review also examines the main causes of deaths and strategies for improving survival including nutrition, shelter and management choice to alter ewe-lamb bonding.

Poor lamb survival limits the achievement of good reproductive efficiency of sheep in many countries. The opportunities for genetic improvement of lamb survival are reviewed, with the prospects found to be better than previously thought. Notwithstanding the importance of good nutrition and management, combinations of direct and indirect selection may ultimately make a valuable contribution to improving lamb survival.

Nutrient and environment related oxidative stress can impact rams and ewes during the reproductive period, resulting in low reproductivity and high lamb mortality. Managing oxidative stress of the newborn by giving ewes large dose of dietary antioxidants, like vitamin E and selenium, could boost immune competency of ewes and lambs to improve lamb survival. A number of related issues remain to be resolved for Australian environments.

Artificial insemination is widespread in the Australian sheep industry so it is important to know if lamb mortality is comparable as with natural mating. This project showed that lamb mortality was similar to natural mating at around 20% with dystocia and starvation-mismothering accounting for 72% of lamb deaths. Therefore artificial insemination can be validly used for sheep reproduction studies.

Birthweight is the single largest determinant of survival in lambs and can be predicted from ewe liveweight at conception and liveweight changes during pregnancy. Coefficients relating ewe liveweight change during pregnancy to lamb birthweights are similar for Merino and Maternal ewes, whereas conception weights of Maternal ewes are significantly heavier than Merino ewes when run together, and lamb birthweights from Maternal ewes are less responsive to ewe conception weights.

Genetic variation in lamb autopsy traits may offer selection opportunities to improve lamb survival. Lambs autopsied in the Australian Sheep CRC information nucleus flocks were used to estimate heritabilites and genetic correlations between traits. While the heritability of lamb survival is low, Lamb ease and thorax circumference appear to be useful indicator traits to improve lamb survival.

Starvation/mismothering is a major cause of lamb loss in the early neonatal period and is related to the ability of the ewe–lamb unit to maintain contact during this time. This study investigates whether Merino lambs from sires selected for high or low loss due to starvation/mismothering differ in lamb vigour, particularly at a time when the ewe would be moving away from the birth site and ewe–lamb contact would need to be maintained. Differences in lamb vigour at this time could help to explain why some sires have consistently high losses due to starvation/mismothering and have potential to be used as a selection tool.

Reproductive rate is an important profit driver in sheep enterprises. The aims of this study were to quantify the relationships between age at first oestrus and yearling reproductive performance, and reproduction performance across age classes in sheep. Our results support the current practice of analysing yearling reproductive performance as a separate trait from later reproductive performance in Australia’s genetic evaluation system and indicate that age at first oestrus is not a reliable measure of sexual maturity in sheep.

Embryo loss represents a major source of reproductive wastage in Merino ewe lambs. Their mean ovulation rate was 150%; however, up to 84% of this potential was lost by weaning. The major contributor to this deficit were losses occurring during the first 17 days after mating. Pregnancy success was significantly higher for ewe lambs from sires with higher breeding values for weight and fat at post-weaning age (8–10 months).

Achieving higher lamb weaning percentages by reducing lamb mortality can improve the profitability of sheep enterprises. We estimated the financial benefits from providing shelter to reduce the mortality of twin lambs on two modelled sheep enterprises in south-west Victoria. The reduction in mortality that could be achieved was a key factor determining benefits and the profitability of sheep enterprises lambing during high chill weather conditions could be improved by providing low cost shelter.

Poor post-weaning survival of sheep in Australia is an important problem but its variation across different production systems is not well described. In this survey of weaner management of 1410 woolgrowers, average weaner mortality was 4.6%, but 44% of farms overall, including 32% of crossbred enterprises, exceeded the recommended mortality benchmark.  However, farm and management factors were identified that could be manipulated to improve survival, in accordance with the findings of smaller, regional studies

Sheep are joined at different seasons to supply the year-round demand from domestic and export lamb markets. Lambing performance was generally higher from crossbred ewes joined in autumn than spring, with winter being intermediate, although there were significant ewe breed x season interactions. Ewe genotypes with higher out-of-season reproduction will be more suited to intensive and accelerated lamb production systems.

The paper is the first in a series and examines the potential to select for reduced fluctuations in weight and fat across the production cycle. The results suggest that neither sire breed nor sire influenced the magnitude of fluctuations in ewe weight or fat in response to environmental and reproductive stress. It is concluded that to avoid low fat reserves and low fertility during ‘tough’ periods, to improve adult ewe body condition and weight selection can be made on post-weaning measurements.

The paper follows on from previous analysis within the series and examines the potential to select for reduced fluctuations in weight and fat across the production cycle. The results suggest that the ewe’s genes do not influence the magnitude of fluctuations in weight or fat in response to environmental and reproductive stress. It is concluded that to avoid low fat reserves and low fertility during ‘tough’ periods, selection to improve ewe body condition can made at any time.

The paper follows on from previous analysis within the series and examines the potential to select for reduced fluctuations in weight and fat across the production cycle in Merinos. The results suggest that the ewe’s genes do not influence the magnitude of fluctuations in weight or fat in response to environmental and reproductive stress. It is concluded that the ability to select against weight and condition change across the production cycle is limited and selection should instead be focussed on optimising ewe condition.