A literature review of the roles of vitamin E in sheep reproduction.

Summary

Improving lamb, weaner and ewe survival are a high priority for the sheep industry. Several projects submitted to the National RD&E Plan for Sheep Reproduction (ISBN: 9781741919943) related to developing nutritional and breeding strategies to modulate immune competency of ewes and their offspring to enhance survival were recommended for further development. There is emerging evidence that the activity of the immune system could play an important role in determining the fitness of animals and their ability to cope with environmental stressors. The two most ‘at risk’ phases of reduced innate immunity in most mammals are in the infant and elderly (Kollmann et al. 2012), and these two periods of reduced immune function coincide with periods of increased mortality in sheep. There is evidence of genetic variation in the development of acquired immunity (Berggren-Thomas et al. 1987), and that selection for higher production results in a reduction in immune response across a range of species (Rauw et aI. 1998). Berggren-Thomas et al. (1987) demonstrated that in ewes that had been inoculated with a foreign antibody, the titres of antibodies in their new born lambs was a heritable trait and was positively associated with their likelihood of survival. There is some evidence that higher genetic potential for wool production is associated with lower lamb survival and weaner survival, although it is not known conclusively whether the reduction in survival is a trait of the lamb or of the ewe or both. Ferguson et al. (2007) reported lower lamb survival from high fleece weight ewes, and recent analysis indicates lambs from high fleece weight sires or high growth sires have lower survival at the same birth weight both pre- and post weaning (Thompson et al, in preparation). Immune capacity can be altered by nutrition, and supplementing animals with vitamin E and selenium (Se) or sulphur amino acids is known to improve immune responses (Morris 2002; Rooke et al. 2008). Several project concepts submitted to the National RDE Plan for Sheep Reproduction proposed further R&D to better understand the potential link between the immune competence of the lamb and its likelihood of survival.
Prior to funding this R&D, MLA commissioned a literature review of ‘Vitamin E status and reproduction in sheep: Potential implications for Australian sheep production systems’. This review has been completed and will also be submitted for publishing in a Special Edition of Animal Production Science following MLA approval. The review focuses specifically on the role of Vitamin E on reproduction of sheep, and how responses to vitamin E could be influenced by other nutrients involved in the management of oxidative stress and immune function such as Se and sulphur amino acids. The main conclusions are that further investigation is justified to quantify the impacts of vitamin E supplementation, in combination with other natural antioxidants lacking in dry pasture, on the quality and quantity of sperm produced and especially the potential to improve lamb survival through boosting maternal innate immunity and vitamin E reserves in the newborn. The justified areas for further research are listed in Appendix 1 (Literature Review).