Effect of controlled exercise on libido in 2-yr-old stallions

Eight sexually inexperienced, 2-yr-old Morgan stallions were used in a consecutive two-phase design with two groups of four stallions each. Each phase lasted 16 wk, with semen collections every 14 d. Libido scores were assigned to stallions during each semen collection. Scores ranged from zero to four, with zero indicating minimum and four representing maximum libido. In Phase 1, four stallions received daily forced exercise for 16 wk, and the remaining four stallions were confined to box stalls. In Phase 2, the previously exercised stallions were confined to box stalls, and the non-exercised stallions of Phase 1 received daily forced exercise. No week X treatment effect (P greater than .05) was found in Phase 1. Exercised stallions, however, tended to have lower libido values than non-exercised stallions from wk 10 through wk 16. A week X treatment effect (P less than .01) was found in Phase 2. Libido scores were lower (P less than .05) over time among exercised stallions, whereas scores of non-exercised stallions tended to remain stable or rise slightly over time. Mean libido scores for exercised and non-exercised stallions were different (P less than .05) at the end of Phase 1 (2.06 +/- .37 and 3.5 +/- .37, respectively). By wk 26, mean libido scores were similar (exercised: 2.62 +/- .34; non-exercised: 2.52 +/- .34). However, by wk 32, libido values for exercised stallions were lower (P less than .05) than non-exercised stallions (1.87 +/- .34 and 2.81 +/- .34, respectively). In general, mean libido scores of the non-exercised group were higher than exercised stallions after 12 wk of forced daily exercise.