Continuous contact with females in estrus throughout the year enhances testicular activity and improves seminal traits of male goats.

The "female effect" consists in the stimulation of males' reproductive activity by different signals emitted by females. This stimulation leads to endocrine and behavioral changes that may modify the seasonal pattern of male ruminants. The aims of this experiment were (1) to describe the local reproductive seasonal pattern of Gabon bucks and (2) to determine if continuous chemical, auditory, and visual contact with does in estrus enhances bucks' testicular activity and improves seminal traits throughout the year and modify their seasonal pattern. We used 16 adult Gabon bucks assigned to two experimental groups: nine bucks remained continuously isolated from females (isolated bucks, group IB) and seven bucks were in continuous chemical, auditory, and visual contact through a fence line with does in estrus (stimulated bucks, group SB). During 13 months, scrotal circumference and testosterone concentration were measured weekly and testicular echogenicity was measured every 2 weeks. Also, sperm motility mass and percentage of abnormal spermatozoa were determined, and sperm concentration and total number of motile spermatozoa were calculated every 2 weeks. Testicular echogenicity was greater in IB than that in SB bucks (P < 0.0001), but there were no differences in scrotal circumference. Overall, testosterone concentration was greater in IB than that in SB bucks (P = 0.04), but from late winter to mid-summer, when testosterone concentration presented basal concentrations, SB bucks had greater values than IB bucks (P = 0.004). Sperm concentration (P = 0.05) and sperm mass motility (P = 0.01) were greater in SB than that in IB bucks, and the total number of progressive motile spermatozoa tended to be greater in SB than in that IB bucks (P = 0.1). The percentage of abnormal spermatozoa was lower in SB than in IB bucks in several time points (P < 0.0001). Testicular and seminal traits were better from the end of the spring until mid-autumn. We concluded that does in estrus stimulated bucks' testicular activity, including better seminal quality and a greater increase of testicular fluid content than bucks isolated from females. However, the general seasonal pattern was not modified by stimulation with does in estrus.