L.LSM.0015 - New approaches to increase the weaning rate of the national sheep flock

Summary

This research addressed the significant industry issue of high lamb mortality prior to weaning with a focus on reducing the negative impacts of oxygen deprivation to twin lambs during the birthing process. Despite progress in genetics, nutrition, and management of ewes, as many as a third of twin lambs die before reaching weaning age, which constitutes both an economic and welfare problem for the Australian sheep industry. This research was targeted predominantly at Merino sheep producers across the southern part of Australia; however, findings should be relevant for all sheep producers. The Australian Merino was selected as it is the predominant breed of sheep in Australia, and they typically exhibit the highest incidence of lamb mortalities. The results of the research will be used to inform sheep producers, nutritionists, livestock advisors and the wider sheep industry of the effects of maternal supplementation of compounds with neuroprotective characteristics on twin lamb survival.

Objectives

The objectives of the project were to: 

Develop commercially relevant and easily adopted supplementation strategies which could be provided to pregnant ewes to increase the proportion of lambs that survive to weaning, 

To develop and understand the effects of melatonin, caffeine, betaine, and amino acids (methionine-choline-lysine, citrulline and arginine) on lamb viability, 

To determine whether supplementing pregnant ewes with melatonin, caffeine, betaine or amino acids can improve lamb thermoregulation following birth and protect the lambs from the damaging effects of intra-partum oxygen deprivation, ultimately increasing lamb survival under both research and commercial sheep production conditions.

Key findings

Melatonin improved lamb survival in Stages One and Two and therefore progressed to Stage Three; however, no improvements to lamb survival were observed on three commercial properties across South Australia and Western Australia. 

Caffeine improved lamb thermoregulation in Stage One; however, in Stage Two, caffeine supplementation reduced lamb survival, and therefore did not progress to Stage Three. 

In Stage One, lambs born to ewes supplemented with betaine in late gestation took less time to attach to the udder and suck following birth compared to lambs born to both control ewes and ewes supplemented with a lower dose of betaine for the duration of pregnancy. Ewes supplemented in late gestation also produced lambs which had greater survival to marking and weaning. However, in Stage Two, there was no effect of betaine supplementation in the second half of gestation compared to control ewes, and therefore, betaine did not progress to Stage Three. 

Several amino acid supplementation strategies were investigated to increase maternal circulating arginine. Citrulline or a combination of methionine, lysine and choline did not increase circulating arginine in pregnant ewes, nor did it affect lamb growth, behaviour, or survival. In 2021, rumen protected (RP) arginine became available and supplementation increased circulating arginine concentration in pregnant ewes and improved lamb thermoregulation in Stage One. In Stage Two, RP-arginine supplementation increased lamb survival to weaning by 12.5% and therefore progressed to Stage Three. Results from three commercial properties across South Australia and Victoria indicated no improvement in lamb survival due to treatment.  However, a fourth study, conducted concomitantly on Turretfield Research Centre under extensive conditions, found a 12% improvement in survival of lambs within the first 24 hours of life, indicative of neurological protection during the birth process.

Benefits to industry

Development of cost effective and easily implemented strategies to improve Merino twin lamb survival is a recognised industry priority and will reduce the financial losses and welfare impacts experienced by sheep producers. The three-staged approach demonstrated in this project was designed to develop a clear pathway to commercial adoption. While melatonin, caffeine, betaine and arginine did not ultimately increase lamb survival on-farm, significant benefits over the course of the project were identified.

MLA action

MLA will be pursuing opportunities to further disseminate the results from this project through the Sheep Reproduction Strategic Partnership.

Future research

Basic research should be conducted on the neuroprotective properties elicited by the four products, particularly melatonin and RP-arginine, on fetal physiology, particularly on those fetuses exposed to prolonged parturition. This would provide a better understanding of the mechanisms involved and enable establishment of a clearer strategy for improving lamb viability in the field. A significant impediment for establishing sound results in the field was accurate delivery of the products via lick feeders and deserves greater attention in the future.