Effect of sexual excitation on testosterone and nitric oxide levels of water buffalo bulls (Bubalus bubalis) with different categories of sexual behavior and their correlation with each other

- To our knowledge, NO levels have never been studied in buffalo bulls having different libido categories.
- To our knowledge, this study is the first study evaluates the effect of sexual excitation on serum testosterone and nitric oxide levels of buffalo bulls having different libido categories.
- This study is the first study evaluate the correlations between serum testosterone and nitric oxide levels besides sexual behavior of buffalo bulls.

We studied the effect of sexual excitation on serum testosterone and nitric oxide (NO) levels in water buffalo bulls with different categories of sexual behavior and their correlation with each other. Buffalo bulls were classified according to their sexual behavior (including reaction time, sexual aggressiveness and mating ability): acceptable (good to excellent) (n = 5), fair (n = 5), and unacceptable (poor) (n = 5) sexual behavior. Blood samples were collected from all animals immediately before and after sexual teasing and/or mounting to estimate the testosterone and NO levels using a commercial radioimmunoassay kit and Griess reaction test, respectively. Comparisons among groups were evaluated using a mixed-design analysis of variance. Pearson's correlation coefficients were calculated to determine the relationship between testosterone and NO levels before and after sexual excitation besides sexual behavior. The level of testosterone before sexual excitation was higher (p ≤ 0.05) in bulls with acceptable and fair sexual behavior than in bulls with unacceptable sexual behavior (0.86 ± 0.01, 0.69 ± 0.02, and 0.29 ± 0.02 ng/mL, respectively). The level of NO was higher (p ≤ 0.05) in bulls with acceptable and fair sexual behavior than in bulls with unacceptable sexual behavior (8.00 ± 0.03, 7.66 ± 0.19, and 6.29 ± 0.33 μM, respectively). Sexual excitation significantly (p < 0.05) increase testosterone and NO levels in bulls with acceptable (1.45 ± 0.01 ng/mL and 19.04 ± 0.32 μM, respectively) or fair (0.92 ± 0.02 ng/mL and 14.95 ± 0.34 μM, respectively) sexual behavior, but not in bulls with unacceptable sexual behavior. The unacceptable sexual behavior bulls had significantly lower testosterone and NO levels than the other bulls. There was a strong correlation and association between serum testosterone and NO levels besides sexual behavior of buffalo bulls. In conclusion, the alteration in the testosterone and NO levels after sexual excitation depends on the sexual behavior category of buffalo-bull. Testosterone and NO can be used to create a sexual behavior score. The testosterone and NO levels of can be predicted via evaluation of sexual behavior of buffalo bull.