This study examines whether the photostimulation of sexual activity in young bucks improves the reproductive performance of the "male effect" in comparison to adult males. The experimental design was a 2x2 with to variables: age of bucks and photoperiodic treatment of bucks. Ninety-three anoestrous does were distributed into four groups depending on the kind of male used: young bucks (1.26 years old, n = 6) or old bucks (5.15 years old, n = 6). Half of each group of males were subjected to a photoperiodic treatment or a natural photoperiod. After the males were introduced, the sexual behaviour of the bucks was assessed for 10 days, and doe oestrous behaviour was recorded. Ovulation was confirmed from plasma progesterone concentration, and ovulation rate was assessed by transrectal ultrasonography. Fecundity, fertility, prolificacy and productivity were also determined. The females in contact with young bucks showed a higher percentage of ovulation (100% vs 81%, P<0.01) and oestrous (82% vs 64%, P<0.05) than females in contact with old bucks. The females in contact with photostimulated bucks showed higher percentages of oestrous (88% vs 60%, P<0.01), fertility (78% vs 44%, P<0.01) and productivity (1.08 ± 0.10 vs 0.60 ± 0.12 P<0.01) than females in contact with control bucks. No interaction between both factors (age and photoperiod treatment) on any studied variable was observed. In conclusion, the response to the "male effect" was higher when using young bucks or photostimulated bucks, and produced 48 additional kids for every 100 females in the mating group compared to does exposed to untreated bucks.
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