Effects of novel females and stage of the estrous cycle on sexual behavior in mature beef bulls1,2

Abstract

The objective of this experiment was to determine the effects of unrestrained females on sexual behavior of bulls. Twelve Angus bulls were used in three Latin square replicates where sexual interactions between one bull and one female were quantified for each of four 60-min tests (T1, T2, T3, and T4, respectively). All bulls received the following treatments: 1) exposure to four estrual females in sequence (A-B-C-D); 2) exposure to two estrual females in alternating sequence (E-F-E-F); 3) exposure repeatedly to one estrual female (G-G-G-G); and 4) exposure repeatedly to one diestrous female (CON). During T1, mount interactions, mounts with intromission and mounting intervals were similar when bulls were in A-B-C-D, E-F-E-F, or G-G-G-G. Fewer mount interactions, no mounts with intromission, and increased mounting intervals (P < 0.05) occurred in CON. During T2, there were more mount interactions, more mounts with intromission, and decreased mounting intervals (P < 0.05) when bulls were in A-B-C-D or E-F-E-F compared with when they were in G-G-G-G or CON. More mount interactions (P < 0.05) occurred in G-G-G-G compared with CON, but mounts with intromission and mounting intervals did not differ. During T3, more mount interactions (P < 0.05) occurred in G-G-G-G than in CON; otherwise, sexual behaviors were similar among treatments. Mounting intervals during T3 were similar among A-B-C-D, E-F-E-F, and G-G-G-G, but were all decreased (P < 0.05) compared with CON. During T4, more mount interactions, more mounts with intromission, and decreased mounting intervals (P < 0.05) occurred when bulls were in A-B-C-D compared with other treatments. Mount interactions were similar when bulls were in E-F-E-F, G-G-G-G, or CON; however, more (P < 0.05) mounts with intromission occurred when bulls were in E-F-E-F compared with G-G-G-G or CON. Mounting intervals during T4 were decreased (P < 0.05) in E-F-E-F compared with the CON treatment, whereas in G-G-G-G, they were intermediate. Mounts without intromission were not affected by female novelty or receptivity, but novel females induced more flehmen responses. In conclusion, novel, females, overall, enhanced sexual activity of bulls; however, bull sexual responses diminished after 2 h, even when a novel female was presented. Estrual females that were repeatedly paired with bulls displayed diminished sexual receptivity, but if mated females were rested for 60 min, they allowed further copulation from familiar bulls that were not sexually sated.

Exposure of prepubertal beef bulls to cycling females does not enhance sexual development

“…As the study progressed, perhaps the bulls became less interested or more accustomed to the presence of the cycling beef females. Perhaps the introduction of novel estrual females every month would have altered reproductive behavior outcomes to be more similar to those found in Bailey et al [17]. Generally, the sexual behavior assessed in the present study do not appear to change significantly with pubertal development and though exposed bulls had ample opportunity to interact with cycling females, display of sexual behaviors are not consistently altered by female presence beyond the periods of being a potential novel stimulus.…”

“…Increased mounts and time spent in the cow area during month three may be a reflection of the change in females used though assessments were conducted almost a month after the new group of females was introduced, ample time for bulls to adjust to their presence before our observations. Bailey et al [17] reported that exposure of mature bulls to novel estrual females for 60 min at a time elicited a greater sexual behavioral response than exposure to either the same female in estrus or to a female in diestrus. After the introduction of the new females in our study during month three, reproductive behaviors either remained relatively constant or decreased.…”

Effects of sequential or group exposure to unrestrained estrual females on expression of sexual behavior in sexually experienced beef bulls1,2

“…Bulls were sequestered in the testing pens, and equal numbers of females were distributed randomly within the pretest observation pens, still sequestered from the bulls. Video-recording equipment was set to capture all events in all pens simultaneously on one video cassette tape as previously described (Bailey et al, 2005). Females were allowed into pens either sequentially and switched every 30 min (SEQ) or as a group for 2 h (GRP; Figure 1C).…”

“…A particular group of females served as sexual stimuli for all three groups of bulls on each test day. Each group of bulls was allowed to observe mounting activity among the females as described previously (Bailey et al, 2005); additionally, the last two groups of bulls were allowed to view heterosexual activity. By consistently monitoring female mounting activity, we were able to ensure that only females allowing mounting were placed with bulls during subsequent tests.…”

“…As we have previously suggested (Bailey et al, 2005), it is difficult to evaluate ejaculation frequency in bulls due to an inability to account for all ejaculations that occur (Bailey, 2003). Hence, we quantified mount interactions, mounts with intromission (i.e., copulation), and mounts without intromission.…”