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Development of sexual behavior has been studied in Hereford bulls. Mounting in response to an estrual female was first observed by 3, 6, and 9 months of age in 18.5, 26, and 48% of the bulls, respectively. By 12 months of age 59% of the bulls had their first ejaculations, whereas by 15 months 78% of the bulls registered a complete service. The number of services increased with age until 18 months of age [75]. In Angus, Brown Swiss, Hereford, Angus × Hereford, and Red Poll the first completed service was observed around 11 months of age [48]. Rearing seems to affect development of sexual behavior, since Hereford calves raised in individual pens had a greater number of services when tested for the first time than bulls raised in groups, although the differences quickly disappeared once these bulls were grouped together [76]. In another study, the influence of the presence of females during bull rearing was evaluated. In the first two hours of being exposed to females in estrus, males raised with females had 73% more services than bulls raised in isolation. However, bulls reared in isolation compared favorably in further tests, illustrating the fact that a learning process occurred rather quickly after exposure to females [77].

Age and experience have major effects on libido and serving capacity test results. An overall increase in test scores has been observed in several studies with yearling bulls when tests were conducted repeatedly over relatively short intervals, indicating that a maturing and/or learning process occurs rapidly after exposure of bulls to females. Exposure of yearling bulls classified as low serving capacity to estrual females for four days resulted in increased serving capacity score when bulls were tested within a week later; 85% of these bulls moved into the medium‐ or high‐serving capacity category [78]. No correlations between the numbers of services at 12 months of age with sexual performance at older ages were observed in Hereford bulls. Only when bulls reached 18 months did individual differences in serving capacity remain consistent from one age to another, i.e. 18, 21, and 24 months [79]. In one study, only 53% of 113 yearling bulls completed a service during 10 minutes of libido testing [80], whereas in a different study with yearling Angus and Hereford bulls the variance of the score obtained during eight libido tests conducted over a two‐month period ranged between 69 and 73% [81]. These observations suggest that attempts to predict sexual performance are likely to be unproductive until bulls can fully express their inherent sexual behavior and serving ability. When adult Angus bulls were evaluated, the time required to complete six services when exposed individually to 10 estrous females increased with age from 31 minutes in two‐year‐old bulls to 43, 55, and 67 minutes in three‐, four‐, and five‐year‐old bulls, respectively [82]. However, in another study no difference in libido score or servicing capacity test results between two‐ and three‐year‐old Angus and Hereford bulls was observed [83].