The objective of the present study was to evaluate the effect of 24 h’ fasting prior to semen collection by electroejaculation on behavioral responses, volume of rectal fecal content, bladder size, penis protrusion, erection, ejaculation stimuli, and ejaculate parameters in young Simmental bulls. Twenty-two Simmental beef bulls with an age of 13.2 ± 1.2 mo (mean ± SD) were used in a prospective randomized blinded controlled cross-over design with two pens fasted for 24 h (n = 9; FAS group), and the other three pens were non-fasted (n = 13; CON group). The bulls were maintained under confined conditions without access to pasture. One week later, the pen treatments were inverted, and semen was collected again under the same conditions and by the same team. The behavioral responses, volume of fecal rectal content, bladder size, as well as the number of stimuli required to obtain penis protrusion, erection, and ejaculation to electroejaculation were measured. The following ejaculate parameters were measured: volume, concentration, spermatozoa motility, and morphology. The behavioral response of the bulls to electroejaculation was not different between the CON group and the FAS group (3.2 ± 0.5 and 3.0 ± 0.7, respectively; P = 0.36). Bladder size was significantly reduced in the FAS group compared with the CON group (2.3 ± 0.8 vs. 2.8 ± 0.9, respectively; P = 0.02). The volume of feces in the rectum was not different between the two groups (CON was 2.3 ± 1.7 and FAS was 3.0 ± 1.8; P = 0.23). Compared with the CON group, the FAS group showed a higher proportion of penis protrusion (100% versus 81.8%, P = 0.10), erection (100% versus 81.8%; P = 0.10), and ejaculation (100% versus 90.9%; P = 0.49). The combined efficiency of penis protrusion, erection, and ejaculation (CE-PPEE) in the FAS group was superior to that of the CON group (P = 0.001). The number of stimuli necessary for penis protrusion, erection, and ejaculation for the CON group were 13.5 ± 3.7, 14.9 ± 3.7, and 20.8 ± 5.8, and they were 15.0 ± 4.2, 16.6 ± 4.2, and 20.2 ± 8.1 for the FAS group. The number of stimuli for penis protrusion (P = 0.09), erection (P = 0.08), and ejaculation (P = 0.77) were no different between the two groups. Ejaculate volume was 4.0 ± 2.6 ml and 4.1 ± 2.3 ml for the CON and FAS groups, respectively (P = 0.90). The motility was 1.4 ± 0.7 and 1.4 ± 0.8 for the CON and FAS groups, respectively (P = 0.72). The concentration of spermatozoa was 336.2 ± 273.1 million and 421.1 ± 300.6 million for the CON and FAS groups, respectively (P = 0.31). The percentage of normal spermatozoa was 50.9 ± 18.8 and 45.6 ± 14.3 for the CON and FAS groups, respectively (P = 0.16). It was concluded that fasting for 24 h prior to semen collection by electroejaculation reduced the bladder size and increased the proportion of bulls with penis protrusion, erection, and ejaculation without any difference detected in behavioral responses, volume of rectal fecal content, and ejaculate parameters.
