Synthetic progestogens are widely used in pig farms, but they may contaminate the environment. We evaluated if chasteberry (Vitex agnus castus), a shrub from Mediterranean areas, could be a natural substitute to synthetic hormones for gilts and could reduce boars' sexual behaviour. Our objective was to analyse 1) the composition of chasteberry fruits, 2) their effect on boars' sexual behaviour and plasma testosterone concentration, 3) their effect on gilts cyclicity synchronisation and plasma progestogens concentration. We showed that fruits contain flavonoids (34µg/g kaempferol, 88µg/g apigenin) using HPLC, phytosterols (5µg/g cholesterol, 31µg/g campesterol, 500µg/g beta-sitosterol, 79µg/g stigmasterol) and steroids (6ng/g pregnenolone, 3ng/g progesterone, 3ng/g 5alpha-dihydroprogesterone, 208ng/g 3alpha-dihydroprogesterone) using GC-MS/MS. Two replicates were conducted with 2 groups of 24 boars fed with 10 g vs 0 g per day of chasteberry fruit powder for 1 to 2 months, starting at 115 to 124 days of age. Plasma testosterone concentrations were lower (P < 0.05; permutation test) in chasteberry (2.27 +/-0.3 ng/ml) compared to control group (3.55 +/-0.59 ng/ml). The number of mounting behaviours in the first replicate was lower in chasteberry group (permutation test). Gilts were fed with 300 g twice a day of chasteberry fruit powder (n = 12) or 0 g (n = 6) or synthetic progestogens (n = 6) for 7 days. Plasma concentrations of progesterone were not different between groups. Analysis of inter-oestrus interval is in progress. In conclusion, we showed that 1) chasteberry fruits contain compounds with progestogen effect, 2) its consumption decreased boar libido in one replicate and plasma testosterone, 3) effects on gilts are under study.