Effect of Selenium Supplementation on Secretion of Reproductive Hormones and Immune Response to Trichostrongylidae Nematodes Infestation in Zulu Sheep Ewes During Oestrous Cycle

The growing resistance of nematodes to anthelmintics has prompted research into alternative control strategies, including nutritional supplementation with micronutrients such as Selenium (Se). Research focusing on the use of mineral supplementation would not only contribute to improvement of animal performance but also to acquaint stakeholders with alternative immune boosting strategies in livestock. Thus, this research assessed how immune response and secretion of reproductive hormones of Zulu ewes were affected by Se supplementation during three oestrous cycles. Due to scarcity of the Zulu sheep breed in the study area, a total of 24 clinically healthy Zulu ewes aged 2-3 years were used and distributed into Se-supplemented (n = 12) and non-supplemented (control) groups (n = 12). Blood sampling was done from 12 ewes (6 Se-supplemented and 6 control) for determining the circulating concentrations of oestrogen (E2), progesterone (P4), Luteinizing Hormone (LH), glutathione peroxidase (GSH-Px), modulation of immunoglobulin G (IgG) and neutrophils at the beginning of the experiment (day 0), during oestrus (day 1), dioestrus (day 12), luteolysis (day 15) and ovulation (day 3) of oestrous cycle. Egg Count Per Gram of faeces (EPG), anaemic levels, Body Condition Score (BCS), Rectal Temperature (RT) & nematode species compositions were recorded from 24 experimental ewes at time points described for blood samples collection and subjected to logarithmic transformation (log10) before analysis using the repeated measures Linear Mixed Model (PROC MIXED) of SAS version 9.4. Results revealed a significantly (p˂0.05) increased overall E2, LH, P4, GSH-Px, IgG, neutrophils circulating concentrations and transformed overall BCS in Se-supplemented ewes. Transformed overall values of Anaemia, EPG, burden of Haemonchus, Ostertagia and Trichostrongylus were significantly reduced (p<0.05) in Se-supplemented Zulu ewes. It is therefore, concluded that, selenium supplementation improved secretion of reproductive hormones by minimising oxidative stress through high GSH-Px activity during different stages of the oestrous cycle. Furthermore, selenium supplementation reduced the burden of Trichostrongylidae, enhanced immune response by increasing secretion of IgG and neutrophils in Zulu ewes during oestrous cycle.