Positive stimulus and sexual behavior of rams

Abstract

The reproductive result of commercial flocks is influenced by rams’ reproductive performance, including their sexual behavior. Although there are pharmacological strategies for improving their sexual performance, organic production systems require hormone free strategies. Rams can be conditioned to positive stimuli such as food that triggers a response associated with positive affective state that could influence sexual behavior. Thus, a positive affective state could be an alternative strategy to improve sexual behavior in rams. Therefore, the aim of this study was to compare rams’ sexual behavior toward an estrous ewe after accessing or not (control) a highly motivating food item (fruit). Initially, the rams' preference to consume bananas or apples was determined, and corneal and rectal temperatures, and heart rate were recorded for 12 rams. The rectal and mean corneal temperature increased after the consumption of the fruits (38.8 ± 0.05 °C vs 39.0 ± 0.05 °C, P = 0.006 and 35.2 ± 0.17 °C vs 36.1 ± 0.16 °C, P = 0.0007 respectively), without significant effects on heart rate. Thereafter, a test was designed to confirm whether they were enough motivated to consume the fruit, when offered close to an unknown subject making deterring behaviors. All rams responded positively to the test, approaching the fruit and consuming it for at least 30 s uninterruptedly in all the tests. For 10 days, rams were daily conditioned to the place where their sexual behavior would be evaluated, by entering a pen to which they were conditioned, in which the ram remained for 20 min with two ewes in the luteal phase immediately after consuming their motivational fruit. Finally, the sexual behavior of each ram was tested with a previous known ewe (in estrous) in two conditions: in the pen where they were conditioned with prior availability of the motivational fruit or in a similar pen to which they were not conditioned, without access to food. In this way, each ram was tested in both conditions with a crossover design. Rams only tended to display more flehmen after eating the positive stimulus than when tested without positive stimulus (P = 0.08). The previous consumption of palatable food did not modify the display of any other sexual behavior. It was concluded that the consumption of a highly motivating food as a positive stimulus did not modify the display of rams’ sexual behavior.