Experience and individual motivation affect the sexual performance of male goats at different times of the year

Introduction: Although there is extensive research on sexual behavior in goats, little is known about the effects caused by individual variations in males.

Objective: The present study aimed to evaluate, on an individual basis, the sexual behavior in developing male bucks, during their first year of life, throughout three times across the year.

Methods: Frequencies and latencies of copulation, recovery period, sniffing, approximation, licking, pawing, flehmen, self-marking, female seeking, and fake mounting were assessed in six bucks. With the sum of the standardized frequencies of each behavior, a sexual index was constructed, where negative values indicate low sexual performance, contrary to high values. At the beginning of the study, males were 10 months old, and when the study was over, they were 17 months old. The study was conducted in three stages: stage 1 (March 3rd to March 25th), stage 2 (April 8th to April 20th), and stage 3 (September 21st to October 12th). Each male was tested in the presence of two receptive females, seven times every third day in each stage, for 10 min each test.

Results: When comparing between males, it was found that male 6 had a longer latency of copulation at stage 2 (P ≤ 0.01) and showed a similar trend toward longer latency at stage 3 (P < 0.09). When comparing within the same male over time, the latency of copulation in male 5 changed across each stage (P = 0.03). At the same time, male 6 showed a tendency to decrease the latency of copulation as the study progressed (P = 0.06). Regarding the sexual index, male 3 had the highest sexual index in stage 3 (P ≤ 0.02); in contrast, males 5 and 6 had the lowest at almost all stages. Finally, males 1, 2, 3, and 4 improved their sexual index as the study advanced (P ≤ 0.01); in contrast, males 5 and 6 did not (P ≥ 0.05).

Conclusions: In bucks, the sexual performance improved with experience, but only in those with high motivation.

1 Introduction

In ruminants, sexual performance generally refers to the male’s natural capacity to breed with a great number of females in a relatively short period of time (Katz, 2007). Within goat production systems, the selection of a buck is based primarily on its physical appearance. Hence, generally, males are purchased or selected for their phenotype, which rarely includes a physical examination of the external genitalia, such as the testes and prepuce, or an assessment of semen quality or libido; in fact, libido is almost never considered (Blockey, 1978; Ridlier et al., 2012). Despite this focus, some studies show that using males without sexual experience and when exposed to females in estrus results in poor performance, compared to sexually experienced bucks (Katz et al., 1988; Katz, 2008). Additionally, many commercial herds use more bucks than necessary during the breeding season, often justifying that some of them will be inactive (Ridlier et al., 2012). These practices indicate that the evaluation of sexual behavior during male selection is often underestimated.

Greater observation of male sexual behavior patterns can help correctly identify and select males with high sexual performance. Evaluating this behavior in young, inexperienced males is important for economic reasons and for managing during the reproductive season (Espinosa et al., 2013). Other factors that can affect sexual behavior include the season of the year and the availability of food while they are grazing. Regarding the time of the year, several studies carried out at the Lagunera region in the state of Coahuila (latitude 26°23′N and longitude 104°47′W) in the subtropical north of Mexico have shown that the reproductive season extends from August to December, with both males and females experiencing a period of rest or decreased sexual motivation from January to April (Delgadillo et al., 1999, 2004; Veliz et al., 2006). Likewise, studies carried out on adult males of meat goat breeds such as the Boer in a tropical region in southern Mexico (coordinates: parallels 16°18′58″ and 16°35′46″ north latitude and meridians 98°21′04″ and 98°43′44″ west longitude) indicate that males show seasonal variations in their sexual performance, showing greater sexual activity in the months of November to May (Ponce-Covarrubias et al., 2023).

Regarding the nutritional status, some studies in goat bucks show that, when the animal has a good body condition score and enough available food, they have a faster ejaculation and higher testosterone levels, compared to those underfed animals with a poor body condition score (Barroso et al., 2000; Morand-Fehr, 2005; Zarazaga et al., 2009).

Another important aspect influencing sexual behavior in domesticated goats is the social environment, which is sometimes partially controlled by humans. However, social hierarchies differ between individuals and can impact the reproductive characteristics and sexual behavior in animals (Fraser and Broom, 1990). In sheep, it has been documented that male sexual behavior is influenced by social status: when a lower-ranked male courts a female in the presence of a dominant male, his sexual performance diminishes, while in the presence of another subordinate male, he exhibits the same sexual performance (Ungerfeld and Alexander, 2024).

On the other hand, some works have shown individual differences in sexual behavior in both juvenile (Mendoza, 2010) and mature bucks (Serrano and Hernández, 2012). However, few studies have explored the relationship between animal development and season with the sexual performance of male goats. Hence, the objective of this study was to evaluate, on an individual basis, the sexual behavior in developing male bucks, during their first year of life, throughout three times across the year. We hypothesize that bucks have individualized variations in sexual ability and that this ability improves as they gain experience.

2 Materials and methods

2.1 Location

The present study was conducted in the Agricultural Teaching Center, Caprine Unit, as well as in the Animal Behavior and Reproduction Laboratory of the Multidisciplinary Investigation Unit of the Facultad de Estudios Superiores Cuautitlán, UNAM. Both places are in the Central Highlands of Mexico at coordinates latitude 19°31´35” N and longitude 99°11´42”W, at an altitude of 2,256 m above sea level, with a C(w0) (w)b(i ′)g-type climate, which corresponds to a temperate subhumid climate with a dry winter and summer rains, with an average rainfall of 600 mm per year and an average annual temperature of 15.7°C (SMN, 2023).

2.2 Animals, location, and maintenance conditions

For the present experiment, six French Alpine bucks were used. Animals were kept under confinement in a 10 m × 15 m roofed stable with a concrete floor. They were fed with alfalfa hay (PC 17% ME 2.36 Mcal/kg), 300 g/day/animal of a commercial concentrate (PC 14%, ME 2.7Mcal/kg), and water ad libitum.

2.3 Procedure

All bucks were evaluated during three different experimental stages in the same year. The first two stages were performed during the sexual resting season, while the third was done when it was already the sexual season:

→ Stage 1, from March 3rd to March 25th, observations were made when the bucks had an average age of 10.8 months ( ± 3.12) and a mean body weight of 48.5 kg ( ± 4.22). During this stage, the males first encountered females in estrus.

→ Stage 2, from April 8th to April 20th, males had an average age of 11.8 months ( ± 3.12) and a mean body weight of 54.6 kg ( ± 4.19).

→ Stage 3, from September 21st to October 12th of the same year, males had an average age of 17.8 ( ± 3.12) months and a mean body weight of 67.83 kg ( ± 4.41).

The sexual capacity of the males was evaluated seven times in each of the three experimental phases (a total of 21 observations for each male). Within each stage, sexual behavior was recorded every third day. The test took place in a 4-m × 5-m pen (Figure 1) and consisted of continuous focal observation for 10 min; we decided to measure during this period because we considered it sufficient for males to exhibit at least two mounts per individual. In the literature on goats and sheep, the duration of sexual capacity tests for males ranges from 10 to 30 min, with an average of 18 min (Price et al., 1986, 1998; Bench et al., 2001; Imwalle and Katz, 2004; Delgadillo et al., 2022). The pen was built of open metal panels. Two adult females in estrus, who already had sexual experience, were placed inside. The estrus was induced with estradiol cypionate (1.0 mg/per female/IM, E.C.P, Zoetis Laboratories^®, México). The females were replaced by others each week, receiving the same hormonal treatment. This procedure was carried out during all three stages studied. The females used during the different experimental stages were also housed in a 10-m × 15-m pen.

Figure 1

Figure 1. Graphic representation showing the experimental pen used for the evaluation of the sexual capacity of six bucks, during three experimental stages throughout the experiment. Adapted from Katz (2008).

Once the experimental process was initiated, the buck was taken from his housing pen to the testing pen, where his sexual behavior was observed. Before any observation was taken, the subject was put in a 1-m² holding area for 60 s (Figure 1), while the females were already placed inside the testing pen. After this time, the door was opened so that the buck could enter the experimental area by his own free will. Two previously trained persons registered behavioral observations, such notations were written in already established formats, and a video camera was used to record all events.

During each test, the latency and/or frequency of the following conducts were registered in the males:

● Copulation latency: the time that elapses when the holding area door is opened until the male first ejaculates inside the female.

● Recovery latency of copulation: the time that a male takes to recover from the first copulation to the next.

● Sniffing frequency: the number of times that a buck sniffs the female, mainly in the genital region, as well as other body parts.

● Approximation frequency: the number of times that a buck approaches the female, mainly by her sides.

● Licking frequency: the number of times that a buck runs his tongue in and out of his mouth while he is near the doe.

● Pawing frequency: the number of times that a buck raises one of his forelimbs and then touches the female, mainly by her sides.

● Flehmen behavior frequency: the number of times that a buck raises his upper lip along with his head.

● Self-marking frequency: the number of times that a buck urinates his face and/or licks his penis.

● Female-seeking behavior frequency: the number of times that a buck hits a doe with his forehead or threatens her.

● Fake-mounting frequency: the number of times that a buck mounts a female, with or without penetration, but no ejaculation.

● Copulation frequency: the number of times that a buck mounts a female, with penetration and ejaculation.

When the sexual capacity test was finished, the bucks were returned to their housing stable.

2.3.1 Sexual response index

To calculate the index for each male, in each stage of the study, the frequency of almost all the behaviors mentioned above was included, except the recovery latency of copulation. To give them a similar weight, the behaviors were standardized (Z, mean 0, SD ±1). The index was constructed by algebraically summing the standardized frequencies of each behavior in each period studied. Because there is no publication in the literature that has used this type of index to evaluate sexual capacity, we based ourselves on the procedure that has been used to construct the maternal index in small ruminants (Poindron et al., 2010; Soto et al., 2021; Cano-Suárez et al., 2025), as well as the methodologies that have been suggested to analyze this type of data (Martin and Bateson, 2007). Index outputs included negative and positive values; thus, a negative score was interpreted as a lower sexual response, and positive values meant a greater response to the test. The calculation of this index was done in the statistical program Systat 13.0 (Chicago, Illinois, USA).

2.4 Statistical analysis

Data were first analyzed using the Kolmogorov–Smirnov test, and it was observed that data did not show a normal pattern of distribution; therefore, a non-parametric statistical analysis was then performed. To compare behavioral parameters among different individuals, a Kruskal–Wallis test was used; subsequent comparisons between two individuals were made by means of the Dwass–Steel–Chritchlow–Fligner and Mann–Whitney U tests. Comparison of individuals in each of the three experimental stages was performed by means of a Friedman test, and comparison between matched stages was conducted by means of the Wilcoxon test (Siegel and Castellan, 1995).

Means with standard error of the obtained data will be presented with a confidence interval of P ≤0.05, and a tendency is considered when P ≥0.06 and 0.1. The statistical analysis was performed using the statistical software Systat 13.0 (Chicago, Illinois, USA).

2.4.1 Sample size calculation

The sexual capacity of the males was evaluated seven times in each of the three experimental phases (a total of 21 observations for each male) [N = 126 (6 males * 21 observations = 126)]. To obtain the power of the test for the present study, the G*Power version 3.1.9.7 program was used. The repeated-measures ANOVA option was selected, within factors, respecting what was mentioned in the statistical analysis section. Given that previous studies on sexual behavior in male goats have reported significant differences between seasons and developmental stages (Ponce-Covarrubias et al., 2023), it was considered reasonable to assume a large effect size (f = 0.40) (Cohen, 1988). With a sample size of 126 repetitions, a significance level of α = 0.05, three measurements, and six groups (each male), the statistical power obtained was 99.99%.

3 Results

3.1 Latency of copulation

When a comparison between the six males was made, it was found that significant differences were present at stage 2 (Kruskal–Wallis test statistic = 16.4, P = 0.006), where male number 6 had a longer response time (Dwass–Steel–Chritchlow–Fligner test statistic = −4.4, P ≤ 0.01, Figure 2). At stage 3, only a trend was observed, in which the males had different responses (Kruskal–Wallis test statistic = 9.7, P < 0.09).

Figure 2

Figure 2. Latency of copulation (mean ± SEM) registered during a sexual capacity test performed on six bucks during three experimental phase that developed during the same year. *, ** Represent differences between males during phase 2, P ≤ 0.01. † Represents a trend P = 0.09 during stage 3 (Kruskal–Wallis test). a, b indicate differences between stages for buck numbers 5 and 6 (P ≤ 0.05, Friedman and Wilcoxon tests).

When a comparison was made of each male in each of the three stages, it was found that the response time of male number 5 significantly varied as each stage passed (Friedman test statistic = 7.1, P = 0.03, Figure 2). Meanwhile, male number 6 showed a faster response time during the test as each experimental stage passed (Friedman test statistic = 5.6, P = 0.06, Figure 2). The rest of the males were not affected by the changes made in each experimental stage.

3.2 Recovery latency of copulation

When a comparison was made between the males, no significant differences were found in any of the three stages (P ≥ 0.05, Figure 3). On the other hand, a comparison of each male throughout the three stages showed that male number 3 presented a tendency to decrease his recovery time (Friedman test statistic = 5.4, P = 0.06, Figure 3).

Figure 3

Figure 3. Recovery latency of copulation (mean ± SEM) registered during a sexual capacity test performed on six bucks, during three experimental stages that developed during the same year. a, b, and c indicate differences between stages for buck number 3 (P ≤ 0.05, Friedman and Wilcoxon tests).

3.3 Sniffing frequency

When comparing all six males in each stage, a significant variation in the frequency of sniffing behavior was found (Kruskal–Wallis test statistic = 11.7, P ≤ 0.03, Table 1). In this sense, the male that presented a higher sniffing frequency was number 3 (Dwass–Steel–Chritchlow–Fligner test statistic = 4.2, P ≤ 0.03).

Table 1

Table 1. Appetitive behaviors (means ± SEM) registered during a sexual capacity test performed on six bucks in three different experimental stages.

A comparison of each individual in each stage also showed that, overall, all males presented different sniffing frequencies in each stage (Friedman test statistic = 6.0, P ≤ 0.05, Table 1). In general, most males increased their sniffing frequency from stage 1 to stage 2 (Table 1).

3.4 Licking frequency

When a comparison was made between all the males, it was found that there was a significant variation in licking frequency in stages 1 and 3 (Kruskal–Wallis test statistic = 11.6, P ≤ 0.03); once again, male number 3 presented the highest licking frequency (Dwass–Steel–Chritchlow–Fligner test statistic = 4.4, P <= 0.03, Table 1).

When comparing the licking frequency between each experimental stage, it was observed that the frequency of licking behavior increased in all males, except for male 5 (Friedman test statistic = 8.0, P ≤ 0.02, Table 1).

3.5 Flehmen behavior frequency

When comparing between males during each stage, a variation in the frequency of this behavior was noticed (Kruskal–Wallis test statistic = 12.7, P ≤ 0.02, Table 1). Males 1 and 2 were the ones who had the highest frequency of the Flehmen behavior (Dwass–Steel–Chritchlow–Fligner test statistic = −4.1, P <= 0.04).

An individual comparison of each male across the experiment showed that only male number 1 had a significant increase in the presentation of this behavior from stage 1 to stage 3 (Friedman test statistic = 8.0, P = 0.02, Table 1).

3.6 Self-marking behavior frequency

When comparing between all males, a variation in the frequency of this behavior in stages 1 and 3 was observed (Kruskal–Wallis test statistic = 11.2, P ≤ 0.05, Table 1). In the second stage, only a trend was noticed (Kruskal–Wallis test statistic = 10.2, P = 0.07). Males 2 and 4 had the highest rates of self-marking behavior compared to the rest of the animals (Dwass–Steel–Chritchlow–Fligner test statistic = −4.0, P <= 0.05, Table 1).

A comparison between stages showed that, once again, males 2 and 4 were the ones with the most significant increase of this behavior (Friedman test statistic = 9.2, P ≤ 0.01, Table 1).

3.7 Pawing frequency

When comparing between males, a variation in the frequency of pawing behavior was found during stages 2 and 3 (Kruskal–Wallis test statistic = 13.0, P ≤ 0.02), with male number 3 being the one who presented this conduct more frequently (Dwass–Steel–Chritchlow–Fligner test statistic = −4.4, P = 0.03, Table 2).

Table 2

Table 2. Appetitive and consummatory behaviors (mean ± SEM) registered during a sexual capacity test performed on six bucks in three different experimental stages.

When comparing between stages, it was noticed that males 2 and 3 showed an increase in the frequency of pawing behavior as the experiment progressed (Friedman test statistic = 6.0, P ≤ 0.05, Table 2).

3.8 Female-seeking behavior frequency

When comparing between males, no significant differences were noticed in every stage (Kruskal–Wallis test statistic = 7.2, P ≥ 0.20). On the other hand, a comparison of each male throughout the three stages showed that most males had different frequencies in their attempts to approach the females (Dwass–Steel–Chritchlow–Fligner test statistic = −4.3, P = 0.03, Table 2). Most males presented an increase in the frequency of approximation as the study advanced (Friedman test statistic = 6.2, Table 2).

3.9 Fake mounting

No significant differences were observed between males in any of the stages (Kruskal–Wallis test statistic = 3.1, P ≥ 0.10). When an individual comparison of each male between stages was made, it was found that most of the males presented significant differences in the frequency of fake mounting. An increase in the frequency of such behavior was observed as the study progressed (Friedman test statistic = 8.3, P ≤ 0.05, Table 2).

3.10 Frequency of copulation

Only in stage 2, significant differences in the frequency of copulation between males were observed (Kruskal–Wallis test statistic = 12.6, P = 0.02, Table 2), while in stage 3 only, a trend was observed (Kruskal–Wallis test statistic = 9.7, P = 0.08). Males 3 and 4 were the ones who showed the highest frequency of copulation (Dwass–Steel–Chritchlow–Fligner test statistic = 4.08, P ≤ 0.05, Table 2).

3.11 Sexual response index

Regarding the sexual index, significant differences were found between the subjects of the study (Kruskal–Wallis test statistic = 12.3, P ≤ 0.03). It was observed that male number 3 had the best sexual index among the rest of the experimental subjects (Mann–Whitney U test statistic = 6.0, P ≤ 0.02, Figure 4); in contrast, males 5 and 6 showed the lowest sexual indexes (Figure 4).

Figure 4

Figure 4. Sexual response index (mean ± SEM): a negative index obtained by a male corresponds to a low sexual response, while a positive index corresponds to a high sexual response. a, b, and c indicate differences between males for each stage (P ≤ 0.02, Kruskal–Wallis test). Asterisks indicate differences between stages for each male (*P < 0.05, **P ≤ 0.01, ***P ≤ 0.001, Friedman and Wilcoxon tests).

A comparison of each male between each stage showed that most of the males improved their sexual index as the study advanced; however, male 3 was the one with the most significant increase as each stage passed (Friedman test statistic = 14.0, P ≤ 0.01). In contrast, males 5 and 6 showed poor improvement in their sexual indexes (Wilcoxon test Z = 2.3.0, P ≥ 0.05, Figure 4).

4 Discussion

The results of this experiment show that the sexual behavior of male goats improves with experience. However, it is affected by factors inherent to each individual, and these factors influence their sexual response regardless of their stage of development. Additionally, the study shows that a buck’s sexual capacity improves as the animal becomes more experienced.

A possible explanation of such results, in the case of the bucks whose sexual behavior improved, is that during the transition from stage 1 to stage 2, the subjects gained sexual experience due to their continuous exposure to a receptive female (for about a month), which had a stimulatory effect and allowed for an increase in the male’s sexual drive. It is important to note that such an effect was also observed during the non-breeding season, where the animals are presumably in a period of sexual rest. This period, according to several studies, encompasses the months from April to May (Delgadillo et al., 1999). Therefore, we can conclude that bucks need to have continuous sexual experiences in order to improve their sexual efficiency, even after they have reached puberty (Imwalle and Katz, 2004), and that the outcome of such biostimulation can be independent of the reproductive season. In agreement with previous findings (Serrano and Hernández, 2012), it was observed that the frequency of appetitive behaviors of the sensory kind (sniffing, licking, flehmen behavior, self-marking) increased in a significant manner from stage 1 to stage 2 and that such an increase was more evident in those males with the best sexual performance. In contrast, bucks whose sexual performance was poor did not present such an increase.

Concerning the third experimental stage, the frequency of appetitive behaviors was high in most of the males. This could be explained by the fact that the breeding season had already begun, which, as previously explained in the latitude of the location where the study took place, encompasses the months from September to January (Delgadillo et al., 1999). On the contrary, continuous exposure to females in estrus did not improve the sexual capacity of those bucks that displayed poor sexual performance from the beginning. This was observed during the first two experimental stages (non-breeding season), as well as in the third experimental stage, when the males were already in the reproductive time of the year (Delgadillo et al., 1999). To our knowledge, these results show, for the first time, that in goats bucks with poor sexual capacity exist and that such a characteristic is independent of sexual maturity and reproductive season. These results can be compared to those reported for other species, such as buffaloes and cows (García et al., 1986; Anzar et al., 1993).

It is important to mention that the frequency of appetitive behaviors (sniffing, licking, flehmen, self-marking) is normally elevated in a sexually active male. Therefore, a behavioral assessment that takes into consideration the conduct evaluated in the present study would allow for the proper identification of individuals with the highest reproductive potential.

Regarding other appetitive behaviors evaluated in this study, it was found that the frequency of approximations to females increased, in most of the subjects, from stage 1 to stage 2, and that it remained that way during the third stage. Such an outcome would have a similar explanation to that described for sensory conducts. Female-seeking behavior is also an important indicator of a sexually active male and, along with the presence of other conducts, has established the foundations for a phenomenon known as biostimulation due to the male effect in goats (Flores et al., 2000; Delgadillo et al., 2002; De Gasperín-Estrada et al., 2008; Moeini et al., 2015).

With respect to pawing behavior, our results show that this conduct was not as evident in most of the bucks during their sexual evaluation; however, those individuals who exhibited this behavior more frequently were also the ones with the highest sexual capacity. Contrary to what was already explained about the individuals whose sexual performance was poor, we must highlight the fact that there are individuals who exceed all expectations and can display a vast behavioral repertoire in order to successfully breed.

In relation to consummatory behaviors, it was found that the number of times the animals displayed fake mount increased, in most of the individuals, from stage 1 to stage 2, and that it remained high during stage 3. This is consistent with that previously reported for appetitive behaviors, in which an improvement in sexual behavior is observed as the male gains more experience and is possibly also associated with the breeding season. On the contrary, bucks with poor sexual performance did not show any increase in fake-mounting behavior, which is like that reported for appetitive behaviors. Breeding attempts are indicative of a buck molding his sexual ability according to his development and his experience, but it could also be assumed that such attempts are also a way for the bucks to get aroused in order to better interact with the doe, given the fact that several studies about goat behavior have reported that those males who are given the opportunity to observe females mounting other females improve their sexual performance (Shearer and Katz, 2006).

Regarding copulation behavior, it was observed that only male number 3 had a significant increase in the frequency of this conduct during the different experimental stages, which correlates with what has been reported for other conducts, with male number 3 being the individual with the best sexual performance. The rest of the males showed only a mild increase, with no statistical significance, in the display of this behavior from stage 1 to stage 2, and remained that way during stage 3, and such lagging in the frequency of this conduct could be associated to the limited duration of the test (10 min), which in turn did not allow a higher frequency to be recorded.

Analyzing the results of the sexual index, we can conclude that the creation of such an index may facilitate the proper selection of a buck during the process of selecting a stud. In the present study, male number 3 had the highest sexual index and best sexual performance, which did not improve during all three stages. In contrast, males 5 and 6 had the lowest sexual performance, which did not improve with more experience or across the breeding season. Talking specifically about response time (the amount of time to perform copulation by the buck), this was short in male 3, and even more, he was the male with the highest frequency of copulation. Accordingly, males 5 and 6 had the slowest response time and the lowest frequency of copulation.

All of this indicates the existence of an individual predisposition of bucks to present a higher or a lower sexual capacity, given the fact that, during the development of the present study, it was observed that such differences between individuals were already present since the earlier stage and that such differences persisted throughout the experiment. Individual variation can be associated with genetic, nutritional, social, and breeding factors (Price and Orihuela, 2010; Kramer et al., 2019). Considering genetic factors, it has been found that bucks present variation in their sexual drive according to their breed, considering that a study conducted on Damascus and Egyptian Nubian bucks found that the former presented better sexual behavior than the latter (Darwish and Mahboub, 2011). In the case of nutrition, several studies on goats have demonstrated that bucks with an appropriate nutritional status exhibit a better sexual performance than those with poor nutritional status (Delgadillo et al., 2006; Zarazaga et al., 2009). Regarding social factors, it has been observed that in both goats and sheep, the social status of an individual plays an important role in their sexual performance, highlighting the fact that dominant males present better sexual performance than subordinate ones (Ungerfeld, 2012; Ungerfeld and Lacuesta, 2015; Ungerfeld et al., 2016).

In the present study, nutritional and genetic factors were kept under control. All the subjects presented good nutritional status throughout the different stages, and only individuals of the same breed were tested. Therefore, the possibility of nutrition or genetics having an impact on the sexual performance of the animals can be ruled out. Additionally, all the subjects were of similar age and were reared under the same conditions, with natural lactation and weaning at 60 days of age. It is thus assumed that 1) individual variation in sexual behavior observed during this study is mainly related to epigenetic factors, which in turn determine the biological efficiency of the individuals, and 2) that it is important to highlight the possible impact of social factors on the results of this study. The latter was not evaluated during the present experiment but could be considered in future studies.

To our knowledge, the results of this study regarding individual variation of sexual behavior in bucks are the first reported data concerning this species; however, such differences between individuals have already been documented in other species such as sheep (Davis et al., 1984; Price et al., 1991, 1992). Similar results have been found in the studies mentioned above, which have also reported the existence of individuals with inherently good or poor sexual performance.

Based on the results of the present study, several conclusions can be drawn. First, we conclude that gains in sexual experience could improve sexual performance; however, this is evident only in some of the males. Additionally, we assert the existence of significant individual differences in the sexual behavior of bucks: some males have great sexual performance, while others have an extremely low performance, which does not improve regardless of experience and reproductive season. Finally, we conclude that the implementation of a sexual index can help during the selection of males for breeding.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement

This study was reviewed and approved by the Internal Committee for the Care and Use of Experimental Animals with folio number CICUE-FESC-C1502 of the Facultad de Estudios Superiores Cuautitlán, UNAM. The study was conducted in accordance with the local legislation and institutional requirements.

Author contributions

KA-P: Data curation, Investigation, Writing – original draft, Writing – review & editing. AT: Investigation, Methodology, Supervision, Validation, Writing – original draft, Writing – review & editing. FG-D: Conceptualization, Methodology, Validation, Visualization, Writing – review & editing. RI-T: Methodology, Validation, Writing – review & editing. PC-S: Investigation, Methodology, Writing – review & editing. RS: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Writing – original draft, Writing – review & editing.

Funding

The author(s) declare financial support was received for the research and/or publication of this article. This research was mainly funded by Universidad Nacional Autónoma de México with project number: UNAM-DGAPA-PAPIME PE206016, K. Ayala-Pereyro was awarded a scholarship for her master’s studies by CONACYT, as well as by a complementary support made by Facultad de Estudios Superiores Cuautitlán with project number: FESC-UNAM-PIAPIC 33.

Acknowledgments

We would like to thank Anaid I. Hernandez García for the support in statistical advice and sample size power calculation. We also thank Laura Ruiz Salas for her support with the care and management of the animals.

Conflict of interest

The authors declare that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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The author(s) declare that no Generative AI was used in the creation of this manuscript.

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