VETERINARSKI ARHIV 68 (6), 219-229, 1998

ISSN 0372-5480
Printed in Croatia

Influence of age and season on body mass, scrotal circumference and sexual behaviour of Nili-Ravi buffalo (Bubalus bubalis L.) bulls

Muhammad Tariq Javed¹*, Ahrar Khan¹ and Razia Kausar²

¹Department of Veterinary Pathology, University of Agriculture, Faisalabad, Pakistan

²DVM Student, Faculty of Veterinary Science, University of Agriculture, Faisalabad, Pakistan

* Contact address:
Dr. Muhammad Tariq Javed,
Department of Veterinary Pathology, University of Agriculture, Faisalabad 38040, Pakistan,
Phone: 92 41 625 834; Fax: 91 41 624 607

JAVED, M. T., A. KHAN, R. KAUSAR: Influence of age and season on body mass, scrotal circumference and sexual behaviour of Nili-Ravi buffalo (Bubalus bubalis L.) bulls. Vet. arhiv 68, 219-229, 1998.

ABSTRACT

A total of 16 buffalo (Bubalus bubalis L.) bulls was divided into four age groups: 3-4, 6-7, 8-9 and 12-15 years of age. Observations made over five seasons (dry summer, humid summer, autumn, winter and spring) showed an overall mean body mass of 689±55 kg. It was greatest (P<0.05) in bulls of 8-9 years of age and was lowest (P<0.05) in summer. The mean scrotal circumference (SC) was 32.6±3.3 cm and showed no difference in age groups, but was lower (P<0.05) in summer. The mean score for libido and mating behaviour was 2.6±0.5 and 4.8±1.0, respectively. The libido showed no difference between age and groups, but mating behaviour was higher (P<0.05) in bulls of 6-7 years of age, while both were lower (P<0.05) in dry summer. The mean time lapse between two ejaculates was 10.8±8.1 minutes, and did not vary between age groups. However, a longer (P<0.05) time period was required to complete a second ejaculate during winter, and a shorter time period during autumn. The body mass showed a positive correlation with libido (r=0.128) and mating behaviour (r=0.107), but was negative with SC (r=0.080). Scrotal circumference showed a positive correlation with libido (r=0.157) and mating behaviour (r=0.099). The time taken to complete a second ejaculate was less in bulls having higher score for libido and mating behaviour.

Key words: body mass, scrotal circumference, sexual behaviour, age, season, buffalo bulls, Bubalus bubalis, Pakistan

Introduction

The body mass and scrotal circumference (SC) are two important parameters in assessing the reproductive efficiency of a male and both are positively correlated in young bulls (AHMAD et al., 1989) and bulls over 18 months of age (CARTER et al., 1980). Determination of SC is an essential aspect of breeding soundness examination and has great value as an indicator of puberty, total sperm production, semen quality, pathological conditions of the testes, as well as the subfertility or infertility of a bull (LUNSTRA et al., 1978; AHMAD et al., 1989; OTT, 1991). More importantly, SC is highly inheritable (OTT, 1991) and is related to age of puberty in daughter and half-sib heifers and their subsequent fertility and productivity (BRINKS et al., 1978). Both body mass and SC are reported to be affected by seasons (AHMAD et al., 1989; YOUNIS, 1996). Studies relating to sexual desire/behaviour has shown that it is largely genetically governed (HULTNAS, 1959). However, factors such as environment, age and management are also responsible for a variation in sexual behaviour (YOUNIS et al., 1980; SHALASH, 1984). Although reports on these parameters are available on Nili-Ravi buffalo bulls, most of the reports are based on a two-season study, i.e., low (summer) and peak (autumn) breeding season. Hence, the present investigations were carried out in order to study the influence of age and season on SC, body mass and sexual behaviour, including libido, mating behaviour and the time lapse between two ejaculates, as well as correlation of these parameters on the basis of whole year's data including all age groups in Nili-Ravi buffalo bulls.

Materials and methods

This study was carried out on 16 randomly selected Nili Ravi buffalo (Bubalus bubalis L.) bulls divided into four age groups as shown below (four bulls in each group), at the Semen Production Unit (SPU), Quadirabad, Sahiwal, Pakistan:

Group 1: 3-4 years Group 2: 6-7 years

Group 3: 8-9 years Group 4: 12-15 years

The year 1 May 1995 to 30 April 1996 was divided into seasons (Table 1). The ambient temperature and relative humidity recorded in the area for the study period was taken from the Cotton Research Station, Sahiwal, Pakistan and is presented in Table 1.

Table 1. Means ±SD of temperature (°C) and relative humidity (%) as recorded during different seasons of 1995 and 1996 in Sahiwal, Pakistan

All the bulls were kept under identical conditions of management, feeding (seasonal fodder) and watering. The bulls were housed individually in pens with sufficient cross ventilation and protection against summer heat, and with an open space for sunbathing in winter.

The monthly body mass of each bull was recorded by using large weighbridge. Measurements of scrotal circumference (in centimetres) were made fortnightly at the area of the largest diameter of the scrotum by using a cloth tape as described by OTT (1991).

The libido and mating behaviour of each bull were recorded at the time of semen collection by assigning a numerical value as described by SINGH and PANGAWKAR (1989), with slight modifications (Table 2). Two ejaculates were collected from each bull and the time period between two ejaculates was noted for each bull.

Table 2. Assessment basis of libido and mating behaviour in buffalo bulls

Data were analysed by applying GLM (General Linear Model for factorial experiments) by using Minitab (10.2) computer software package (ANON., 1994). The means were compared by Tukey's test for confidence interval. Correlation coefficients between different parameters were also calculated by using a Minitab computer software package (ANON., 1994).

Results and discussion

Body mass

The overall mean body mass of Nili-Ravi bulls observed during the present study was 688.7±54.7 kg, which was close to an already reported body mass of 674.0 kg for the same breed (HEUER et al., 1987). ANZAR (1984), ASGHAR et al. (1985), AHMAD et al. (1989) and YOUNIS (1996) had reported lower body mass of 665.0, 652.0, 625±2 and 662.0±6.0 kg, respectively, for the same breed. The difference in body mass could be due to the difference in the number of observations made, or the number of animals included in studies, or the nutrition and/or season of study.

The results of body mass showed that bulls of 8-9 years had a higher (P<0.05) body mass compared to 3-4 and 12-15 year old bulls (Table 3). Similarly, AHMAD et al. (1985) reported an increase in body mass with age, from 625.4±20.4 at four years, to 789.0±19.8 at nine years. Thereafter, it decreased to 762.3±32.2 kg at 14 years of age. YOUNIS (1996) has also reported a higher (P<0.05) body mass in adult bulls (674.9±15.1 kg) than in old (660.3±8.3 kg) and in young (651.9±4.7 kg) bulls. It can be inferred from these findings that body mass increases with age and reaches a maximum at around nine years of age. Thereafter, its decrease may be due to a characteristic of breed.

Table 3. Comparison (means ±SD) of body mass and scrotal circumference of different age groups of buffalo bulls in different seasons of the year in Pakistan

Values of each parameter in each row with different small letters, and in each column with different capital letters, are statistically different (P<0.05)

Body mass in the present study was lower (P<0.05) in summer compared to other seasons (Table 3). Similarly, HEUER et al. (1987) and YOUNIS (1996) recorded a lower (P<0.05) body mass in summer compared with autumn in Nili-Ravi bulls. Body mass in autumn, winter and spring was statistically similar. This indicates that summer affects body mass and causes a decrease in later years, which might be due to the effect of high ambient temperature on body condition and to the unavailability of quality green fodder. Poor management with regard to watering and showering during summer appeared to be another factor contributing to a low body mass. It has been reported that 60-80% of body mass is influenced by environmental factors (HEUER et al., 1987; AGUIAR et al., 1992). The genetic increase in growth rate favours the growth of lean tissue relative to fat, while the environmental increase in growth rate favours the growth of fat tissue relative to lean tissue (KOCH et al., 1982).

Scrotal circumference (SC)

The overall mean SC observed during the present study was 32.6±3.3, which is comparable to 33.3±3.9 cm reported by YOUNIS (1996) and was also close to the 34.0 cm reported by ANZAR et al. (1993) for the same breed. However, it was smaller than 38.5 cm (AHMAD et al., 1987) as they had kept bulls on a high energy diet. The effect of the latter on SC has also been reported by MADRID et al. (1988).

The SC did not differ significantly between age groups but was relatively higher in bulls of 12-15 and 6-7 years of age, compared to those of 3-4 and 8-9 years of age (Table 3). These findings were comparable to those of YOUNIS (1996), who also observed lower (P<0.05) SC in young bulls (31.6±0.4 cm) compared with adult (35.1±0.1 cm) and old (34.4±0.9 cm) bulls. Similarly, ANZAR (1984) and AHMAD et al. (1984) reported an SC of 36.4 and 34.5 cm in adult bulls, respectively. In a later study, AHMAD et al. (1985) reported higher SC (37.5 cm) in adult bulls. Similarly, a much greater SC (39.00 cm) has been reported by ASGHAR et al. (1985). Variations in SC in different reports might be due to the effect of nutrition, as already mentioned, or a difference in the season of study, and perhaps also due to variations in the number of bulls included in different studies. The lower (P<0.05) SC observed in bulls of 8-9 years of age during the present study (Table 3) was due to presence of two bulls with small SC (an overall mean SC of 30.4±0.9 and 25.5±0.6 cm, respectively). It has been stated that SC increases rapidly in young bulls, only gradually in mature and that it declines in old ones. The latter case indicates senile atrophy (AHMAD et al., 1984; MCENTEE, 1990; COULTER, 1991; WILDEUS, 1993). This appears to be true in the present study also, as SC increased in 6-7 years old bulls and may have further increased (an exception here due to two bulls with small SC) and have declined thereafter in old bulls.

The SC was significantly (P<0.05) lower in summer compared with winter but was relatively lower than in autumn and spring (Table 3). These findings were comparable with those of YOUNIS (1996) who reported smaller (P<0.05) SC in the low breeding season (summer, 31.4±0.4 cm) than in the peak breeding (autumn, 34.0±0.7 cm) season. Similary, AHMAD et al. (1989) and AGUIAR et al. (1992) have also reported smaller SC in summer compared with colder seasons. The small SC during summer is ascribed to thermal degeneration of the testes, the effect of high ambient temperature (AHMAD et al., 1984; COULTER et al., 1988; AGUIAR et al., 1992). The seminiferous tubules make up 77% of testicular volume (AMANN, 1962), and increased environmental temperature may have a deleterious effect on these tubules (AGUIAR et al., 1992) resulting in a smaller volume of the testes and hence a smaller SC. Alternatively, the hypothalamic-pituitary axis may have been adversely affected by the high humidity and temperature, resulting in decreased GnRH secretion and reduced seminiferous tubule volume (FIELDS et al., 1979). However, in winter, the availability of lush green fodder, rich in vitamin-A and minerals, increases the plasma oestradiol level, which plays a vital role in the activation of hypothalamic-pituitary axis, with an ultimate increase in plasma testosterone levels causing activation and enhancement of spermatogenesis, leading to an increase in testes size (AMANN et al., 1986; AHMAD et al., 1991).

Sexual behaviour

The overall mean for libido and mating behaviour score observed during present study was 2.6±0.6 and 4.8±1.0, respectively. A higher libido score has been reported by YOUNIS (1996) and ANZAR et al. (1988) in the same breed (3.9±0.1 and 4.9, respectively). A libido score of 4.0 was observed in cow bulls (CHENOWETH, 1981). The variation observed in libido score in different studies could be due to variations in the scoring system or a variation of assessment in recording observations. However, there appeared to be little difference in the libido score of buffalo and cattle bulls.

The libido score differed insignificantly, while mating behaviour was significantly different (P<0.05) between age groups and was higher in bulls of 6-7 years of age (Table 4). Similar observations have been made by SHALASH (1984) and YOUNIS (1996). They also reported a higher libido in adult than in young and old bulls. The greater body mass and SC observed during the present study in the same age group (6-7 years) indicates effect of these parameters on the libido and mating behaviour of the bull. According to ANZAR (1984) sexual behaviour also differed significantly (P<0.05) among bulls having different scores for age, body mass and SC. SHALASH (1984) and YOUNIS (1996) also reported that the age of the bull was found to be responsible for the variation in libido.

Table 4. Comparison (means ±SD) of sexual behaviour of different age groups of buffalo bulls in different seasons of the year in Pakistan

Values of each parameter in each row with different small letters, and in each column with different capital letters, are statistically different (P<0.05)

The libido and mating behaviour score varied significantly (P<0.05) in different seasons, with both being lower in the dry summer season (mating behaviour also varied in a humid summer) compared to other seasons (Table 4). The libido, however, was significantly higher in spring than in all other seasons, although mating behaviour showed no statistical difference in autumn, winter and spring (Table 4). These findings were comparable to those of YOUNIS (1996), who studied only two seasons and who reported a higher libido score during autumn (4.3±0.1) than in summer (3.5±0.2). Similarly, AFIEFY et al. (1984), LI et al. (1988) and AHMAD and NOAKS (1995) reported a high degree of sexual desire in bulls during cold months than in hot. This is ascribed to the availability of highly nutritive green fodder rich in minerals and vitamin-A. The standard plan of nutrition improves sexual activity (LI et al., 1988) and it is known that vitamin-A deficiency results in a lowering of the libido in bulls (AFIEFY et al. 1984). The lower libido and mating behaviour scores observed in summer during the present study could be due to the effect of heat stress, which depresses thyroid gland activity (ARTHUR, 1975; LI et al., 1988) and consequently the sexual desire of bulls (AFIEFY et al., 1984). According to HEUHER et al. (1987), no loss of libido would occur during low breeding season if better management practices were used. The plasma testosterone concentration in buffalo bulls has a positive correlation with libido (BLOCKY and GALLOWAY, 1978; GUPTA et al., 1984). However, libido is largely determined genetically (LAGERLOF, 1938; BANE, 1954; HULTNAS, 1959; GUPTA et al., 1984) and any difference in sexual desire between individual animals is due to the genetically conditioned responsiveness of the target organs rather than to testosterone levels (GUPTA et al., 1984).

The overall mean time lapse between two ejaculates observed during the present study was 10.8±8.1 minutes and did not vary between age groups (Table 4), but was higher than the 8.5±0.2 minutes in the same breed as reported by YOUNIS (1996). The present study showed that a longer (P<0.05) time period was required to complete a second ejaculate during winter, and a shorter time period during an autumn following a dry summer (Table 4). This was comparable with the findings of YOUNIS (1996), who reported 10.63±0.23 minutes to complete the second ejaculate during the low breeding season than the 7.32±0.22 minutes required during the peak breeding season. Similarly, HARANATH et al. (1982) and ANZAR et al. (1993) reported a longer time period required to complete a second ejaculate during the low breeding season than during the peak breeding season. The longer time period required to complete a second ejaculate during winter in the present study could be due to the effect of low temperature (a physical factor) in reviving sexual activity, as the semen collection site was fully open with no side walls, and the time of collection was also early morning before sunrise, in the coolest hours of the winter season and with frequent fog during that period.

Correlation

The body mass showed a positive correlation with libido (r=0.13) and mating behaviour (r=0.11), which was similar to that observed by ANZAR (1984) in sexual behaviour (r=0.48) in Nili-Ravi bulls. However, it showed a negative correlation with SC (r=-0.08). HAHN et al. (1969) stated that heavy and fast growing bulls do not necessarily have larger testes. SC also showed a positive correlation with libido (r=0.16) and mating behaviour (r=0.10). CHENOWETH (1981), however, reported that libido in bulls is apparently not related to SC, but rather that it is a genetic characteristic.

The time taken complete a second ejaculate during the present study was less in bulls having a score for libido and mating behaviour and later correlated positively (r=0.66) with each other. Similar observations were made by ANZAR (1984) who also reported significant (P<0.01) correlation of libido with mating ability (r=0.89).

Conclusions

It can be concluded from the present findings that Nili-Ravi buffalo bulls around the age of 6-7 years exhibit maximum sexual desire and sexual performance. However, SC and body mass were at their maximum at the age of 8-9 years. It can also concluded that the body mass and SC of Nili-Ravi bulls are lower in summer only as far as libido and mating behaviour scores (dry and/or humid) are concerned, while all parameters were statistically similar in autumn, winter and spring, except for libido, which was higher (P<0.05) in spring.

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Received: 22 January 1998
Accepted: 26 October 1998

JAVED, M. T., A. KHAN, R. KAUSAR: Utjecaj dobi i godisnjeg doba na tjelesnu masu, opseg mosnje i spolno ponasanje nili-ravi bivolskih (Bubalus bubalis L.) bikova. Vet. arhiv 68, 219-229, 1998.

SAZETAK

Ukupno 18 bivolskih (Bubalus bubalis L.) bikova podijeljeno je u 4 dobne skupine: 3-4, 6-7, 8-9 i 12-15 godina. Promatranja tijekom 5 godisnjih doba (suho ljeto, vlazno ljeto, jesen, zima i proljece) su pokazala prosjecnu tjelesnu masu od 689±55 kg. Masa je bila najveca (P<0,05) u bikova dobi 8-9 godina, a najmanja (P<0,05) ljeti. Prosjecni opseg mosnje je bio 32,6±3,3 cm bez razlika medu skupinama, ali je bio manji (P<0,05) ljeti. Prosjecni rezultat za libido je bio 2,6±0,5, a za parenje 4,8±1,0. Libido nije bio razlicit medu dobnim skupinama, ali rezultat za ponasanje pri parenju bio je visi (P<0,05) u bikova dobi 6-7 godina, a oboje je bilo nize (P<0,05) za suhog ljeta. Prosjecno vrijeme izmedu dvije ejakulacije je bilo 10,8±8,1 minuta i nije variralo medu skupinama. Medutim, zimi je trebalo vise, a jeseni manje vremena da se izvrsi druga ejakulacija (P<0,05). Tjelesna masa je pokazala pozitivnu korelaciju s libidom (r=0,128) i parenjem (r=0,107), ali je bila negativna s opsegom mosnje (r=0,080). Vrijeme potrebno za zavrsavanje druge ejakulacije bilo je krace u bikova s visim rezultatom za libido i parenje.

Kljucne rijeci: tjelesna masa, opseg mosnje, spolno ponasanje, dob, godisnje doba, bivol, Bubalus bubalis L., Pakistan