Abstract
Background:
According to many authors, the supplementation with a combination of probiotic and bioactive plant influences the sexual activity and improves sperm production in rams out of the mating period. It has also reported to increase ejaculate volume, to improve sperm motility and concentration, and to result in low abnormal sperm percentage.

Aim:
The aim of the present study was to investigate the influence of the combination of bioactive substances contained in three plant species (Thymus vulgaris L., Origanum vulgare L. and Tribulus terrestris) and a probiotic - ZOOVIT LL, on some basic indicators of ram semen out of the breeding season.

Methods:
The study was conducted at the experimental base of the Agricultural Institute - city of Stara Zagora for 2 months in 2025. Eighteen clinically healthy rams of the Bulgarian Dairy Synthetic Population (BDSP) breed, aged 3 to 5 years, raised indoor in group pens with outdoor yard for walking, were the subjects of the study. A control group - CG, was fed grass hay and 1.2 kg of compound feed. Experimental group 1 - EG1 received grass hay, 1.2 kg of compound feed with supplement (Tribulus terrestris 4 g/kg, Thymus vulgaris L 2 g/kg and Origanum vulgare L 2 g/kg) per animal/day and experimental group 2 -EG2 - grass hay, 1.2 kg of compound feed with supplement (Tribulus terrestris 4 g/kg, Thymus vulgaris L 2 g/kg and Origanum vulgare L 2 g/kg) + ZOOVIT LL 120 ml per animal/day per animal/day manufactured by the “LB Lact BAS” Laboratory.

Results:
The combined administration of bioactive substances and probiotic (EG2) resulted in the highest ejaculate volume (1.14 ± 0.16 ml) and sperm concentration (4.54 ± 0.55 x 10⁹/ml) at day 49 (P≤0.05). At the same time, a significant increase in progressive motility from 53.60% to 72.10% (P≤0.001) was observed.

Conclusion:
The co-supplementation of BDSP ram diets with plant bioactive substances and probiotics enhanced significantly and sustainably the key ex vivo semen quality indicators (ejaculate volume, sperm concentration, total and progressive motility) via synergistic effects; however, in vivo field trials are necessary to validate if this better semen quality translates into superior pregnancy rates.

Key words: Origanum vulgare L.; Thymus vulgaris L.; Tribulus terrestris; Ram semen; Probiotic.