192 Effect of selenium supplementation and oestrous synchronisation protocols on reproductive performance of Merino ewes

There is currently an increase in the use of micronutrients to minimise the impact of environmental effects, such as heat stress, on reproduction. Selenium (Se) is one of the micronutrients that its use has gained attention currently due to its antioxidant capacity. This study was aimed to evaluate the effect of Se supplementation and oestrous synchronisation on reproduction performance of Merino ewes. 60 ewes used for the study were subdivided into two groups of Se supplementation and control. The two groups were further subdivided into two groups based on synchronisation protocol. 30 ewes received sodium selenate 0.34 mg selenium (Se)/kg bodyweight and the 30 ewes from control group received saline water. The oestrous cycles of all 60 ewes were synchronised using controlled internal drug release (CIDR G^®, Zoetis) containing 0.3 g progesterone (P4) inserted intravaginally for 11 days. At removal of CIDR, 30 ewes were intramuscularly injected with 300 IU equine chorionic gonadotrophin (eCG) while the other 30 ewes were subjected to the introduction of four rams wearing aprons who stayed with the ewes for a period of 96 h. Data collected included the onset of oestrus, duration of oestrus, gestation length, glutathione peroxidase (GSH-Px), cortisol, oestradiol (E2), and P4 concentrations. The data was analysed using General Linear Model (GLM) of SAS version 9.4. The oestrous response, distribution of oestrus, conception rate, pregnancy rate, and lambing rate data were analysed using chi-square test. Selenium supplementation had no effect (P > 0.05) on oestrous response, onset of oestrus, duration of oestrus, distribution of oestrus, conception rate, non-return rate, gestation length, or lambing rate. Oestrous synchronisation protocol, on the other hand, affected oestrous response (P < 0.05). CIDR plus eCG ewes had higher oestrous response (P < 0.05) than CIDR plus male ewes. The concentrations of GSH-Px, E2, and P4 were not affected (P > 0.05) by either Se supplementation or oestrous synchronisation. The non-supplemented ewes had high (P < 0.05) cortisol concentration at CIDR removal. In conclusion, CIDR plus eCG oestrous synchronisation protocol improves oestrous response. However, selenium supplementation and oestrous synchronisation do not affect the onset of oestrus, duration of oestrus, conception rate, non-return rate, lambing rate, or gestation length. Both oestrous synchronisation protocols were equally efficient in synchronising oestrous.

The National Research Foundation is acknowledged for funding the study under Project number 116228.