Anti-leptin vaccination to increase growth rate and fertility in Merinos

Summary

The value of sale lambs is of enormous importance to the profitability of sheep production. Ewe reproduction, particularly lamb survival, is identified as a priority field of research because it is critical in underpinning the profitability of lambing systems.

Flock reproduction rate, measured as the number of lambs marked or weaned per ewe joined, is heavily influenced by litter size and to a lesser extent by fertility, both of which are relatively easily improved through nutrition of the ram and ewe. Lamb survival too, can be greatly improved by ewe nutrition. Current extension packages, such as Bred Well Fed Well and Lifetime Ewe Management have been successful in improving the nutritional and genetic status of flocks that both increases the number of lambs born and weaned and also assists in reducing in lamb mortality.

The current extension packages and much of the findings from previous research have demonstrated methods to improve the number of lambs marked or weaned by minimising the highest potential levels of mortality, rather than by lowering the minimum level of mortality, thus opportunities continue to exist for further improvement.

A pilot study was undertaken by co-investigator, Professor Jim McFarlane, which examined the potential for an anti-leptin vaccine to affect ewe reproduction. That study, undertaken over two years, revealed an increase in weaning rates from 102% to 150%.

Similar to the potential of the vaccine against androstenedione, inhibin and bone morphogenetic protein, an anti-leptin vaccine appeared to increase ewe fertility and litter size. Uniquely, lamb survival appeared to improve, too. Given a market already exists for the anti-androstenedione vaccines, but one limited to crossbred ewes and not readily applicable to producers using Merino ewes, it was appropriate that investment was made to further examine the potential of the anti-leptin vaccine, particularly one that may improve lamb survival and can be used in Merino ewe populations.

A study was established to examine the potential for an anti-leptin vaccine to improve ewe reproduction rates. This study used ewe lambs (n=70) and ewe hoggets (n=218), which were mated over two years of reproduction, as lambs and hoggets and in the following year as hoggets and young adult sheep.