Relationship between testosterone and penile spicules in Guinea pigs (Cavia porcellus)

Understanding the physiology of penile spicules in guinea pigs (Cavia porcellus) may improve their management in large-scale production guinea systems. Here we examined whether penis spicule development depends on testosterone and whether exogenous testosterone can reverse penile spicule atrophy in castrated guinea pigs. The relationship between total testosterone (TT) and the development of penile spicules (DPS) in guinea pigs was explored in two experiments. The first experiment described the TT and DPS curves in non-castrated guinea pigs (E1-G1) and guinea pigs castrated on day 35 (E1-G2). In the second experiment, the dose-dependent effect of the administration of exogenous testosterone (ET) was evaluated during DPS in Group 1 (E2-G1; castrated guinea pigs + 125 μg ET on days 65 and 80 of age), Group 2 (E2-G2; castrated guinea pigs + 250 μg ET on days 65 and 80 of age), Group 3 (E2-G3; non-castrated guinea pigs), and Group 4 (E2-G4; castrated guinea pigs without ET). Analysis of variance using a General Linear Model (GLM) was performed. TT increased from day 20 to day 35 in both groups in the first experiment (P > 0.05). This increase in TT was maintained in E1-G1 on days 50, 65, and 80; however, TT fell to basal values in E1-G2 after castration. DPS guinea was directly related to TT level. In Experiment 2, guinea E2-G1 and E2-G2 animals that received ET showed an increase in TT, significantly differing from E2-G4 (P < 0.05). Nevertheless, ET administration in E2-G1 and E2-G2 was not sufficient to reach the TT levels in E2-G3. DPS was closely related to TT levels, such that when testicles were removed, the spicules began to atrophy without disappearing. Our results suggest that TT in guinea pigs increases steadily until puberty completes, after which it decreases and stabilizes and shows an association with DPS. Furthermore, 12-35% of TT produced by guinea pigs is testicle-independent. Finally, ET administration can stop and reverse the spicule atrophy process in castrated males. These results will help to manage guinea pigs in a more sustainable way in countries where this species is of utmost relevance to provide the population with the meat of high quality.