ABSTRACT
The aim of this study was to determine if a single administration of dinoprost tromethamine before each test enhances sexual behaviour in inexperienced rams, and if the possible effect is maintained after the rams gain sexual experience. The study was conducted in northeaster Mexico during autumn (breeding season). The study was performed with 26 Saint Croix rams (16.1 ± 1.1 months old). Rams were allocated to two treatments, which were subjected to 15 tests with 2 restrained non-oestrous ewes. While rams from one group (group DIN) received a single dose of dinoprost (10 mg im, Lutalyse, Zoetis) immediately before the test, the other rams remained untreated (group CON). Sexual behaviours were recorded during 5 min. The data were analysed with a mixed model that included the treatment, number of test and their interaction as main effects, and the individual as a random effect. DIN rams displayed less ano-genital sniffings (6.6 ± 0.8 vs 9.7 ± 0.8, P = 0.007), matings (0.11 ± 0.05 vs 0.29 ± 0.05, P = 0.03), and had a lower mating/total mounts ratio (0.05 ± 0.03 vs 0.16 ± 0.03, P = 0.006) than CON rams. There were no other treatment effects, but there were significant effects of time and interactions between treatment and time in all the behaviours. Overall, administration of a single dose of dinoprost before testing did not have positive effects in the development of rams' sexual behaviour, and even, might have negative effects. However, it should be considered that in this study only one prostaglandin analogue, one dose of this analogue, administered immediately before the tests was used, so more studies involving other analogues, doses, and/or regimes of administration should be done.