Effects of Dietary Thyme (Thymus vulgaris) and Fish Oil on Semen Quality of Miniature Caspian Horse

Thyme (Thymus vulgaris) is a subshrub from the lamiaceae family with plants that are rich in essential oils and antioxidative phenolic substances. The aim of the study was to investigate the effect of dietary thyme and fish oil supplementation on the semen characteristics of miniature Caspian horse. Sixteen stallions were randomly allocated into four groups and received four different diets: unsupplemented control diet, supplemented with fish oil at 2.5% dry matter intake (DMI), supplemented with fish oil (2.5% DMI), and thyme (0.02% DMI), and supplemented with thyme (0.02% DMI). All experimental diets were formulated according to National Research Council (1998). Semen was collected at 0, 30, 60, and 90 days. The semen samples were cooled and preserved at 5°C. Cooled diluted semen samples were evaluated in vitro by microscopic assessments of chilled sperm motility, acrosomal and other abnormalities (head, midpieces, and tail), viability (evaluated by Eosin–nigrosin), and plasma membrane integrity (evaluated by hypo osmolarity swelling test), and the level of malondialdehyde (MDA) was determined during cool storage 0, 24, and 48 hours after collection. The results showed that total and progressive sperm motility and plasma membrane integrity and functionality in all groups were significantly decreased with increasing storage time. On the other hand, the level of MDA in all groups was significantly increased with increasing storage time. Also, the results showed that most sperm quality parameters in this study were significantly higher in fish oil–thyme and fish oil group compared with thyme and control groups after 24 and 48 hours of storage at 5°C. We concluded that dietary supplementation of fish oil and thyme can improve sperm quality in miniature Caspian stallions during storage in cool condition via increasing total and progressive motility and plasma membrane integrity and functionality. More advances in vitro evaluations and artificial insemination are required to reveal the exact effects of thyme on miniature Caspian stallion sperm quality and its fertilizing ability.