Changes in Testicular Biometry and Ejaculate Characters during Pubertal Age in Black Bengal Kids

Productive and reproductive performances of farm animals regulate the economic efficiency of the farming. It is crucial to select the animals for breeding at an earlier age so that they can be utilized effectively for a longer period. Testicular growth of buck is closely related to the live weight and age of buck (Souza et al., 2011). Scrotal circumference is an indirect indicator that gauges the size of the testicles. The onset of puberty is ascertained by the first presence of spermatozoa in seminiferous tubules, epididymis and ejaculates (Kridli et al., 2006). Bengal goats (Capra hircus bengalensis) are distributed in Eastern and North Eastern Hill states of India as well as in Bangladesh. Bengal goats are known for their superior quality meat and skin, adaptability, fertility and prolificacy. The present study aimed to determine the influence of age and body weight on testicular attributes as well as semen characteristics in growing Black Bengal bucks and to determine the onset of puberty in Bengal bucks.
       
The present study was carried out at ICAR-National Dairy Research Institute (NDRI), Eastern Regional Station, Kalyani, West Bengal, India, during the months of November, 2021 to June, 2022. A total of eight Black Bengal males aged four months were selected and maintained under standard managemental conditions. Body weight, scrotal circumference and testicular biometry of males were recorded at 15 days interval during the study period. Length (L), width (W) and thickness (T) of testis were measured with the help of the Vernier caliper. The volume of each testis was calculated using the Lambert formula:
Where:
L = length.
W = Width.
T = Thickness.
       
Semen collection was attempted from four months of age onward with an artificial vagina using an estrus female as a teaser, at weekly intervals. Presence of motile sperm cells in the ejaculate was considered as the onset of puberty in the male. The sperm concentration was estimated by an Accucell photometer (IMV Technologies, France), live sperm cell count was carried out with eosin-nigrosin stain, sperm abnormalities were screened with Rose Bengal staining and plasma membrane integrity of sperm cells was ascertained with hypo osmotic swelling test (HOST). The data of fresh semen were subjected to normality test and found showing a normal distribution. Subsequently, data were analyzed by one-way ANOVA followed by Duncan’s multiple range test and considered as significantly different when P<0.05 or P<0.01. The analysis was carried out using SPSS software (version-26.0).
       
The mean body weight (BW) of male kids at 4 months was 6.86±0.54 kg which significantly (P<0.01) increased with advancing age till 9 months. Mean scrotal circumference (SC) varied from 14.04±0.37 to 18.63±0.31 cm; the testicular length from 4.84±0.15 to 5.59±0.1 cm and 4.91±0.14 to 5.63±0.11 cm in the right and left testis respectively, during the observation period (Table 1). The mean testicular width (RTW) varied from 3.4±0.13 to 3.91±0.11 cm in the right testis and 3.41±0.09 to 3.85±0.11 cm for the left testis. The thickness of the testis ranged from 2.8±0.15 to 3.4±0.09 cm and 2.99±0.13 to 3.52±0.08 cm for the right and left testis, respectively (Table 2). The mean testicular volume ranged from 34.22±2.45 to 54.02±3.05 cm³ at the 4^th and 12^th months of age, respectively. The mean scrotal skinfold thickness (SST) varied between 0.1±0.01 and 0.33±0.02 cm. Body weight and scrotal/testicular biometry measurements of Bengal kids had increased gradually over the period during the 4^th to 12^th months of age and differed significantly (P<0.01). The increase in testicular measurements with advancement of age was in accordance with the earlier reports in different goat breeds (Gogoi et al., 2005; Akpa et al., 2013 and Kumbhar et al., 2019). Chaudhari et al., (2018) reported that all the testicular parameters were significantly affected by body condition /growth rate while Akpa et al., (2013) suggested that bucks with higher body size might possess larger testicular size which might invariably result into a good reproductive capability, better semen quality and thus improve the fertility of the animal.




       
Very few immature sperm cells in the ejaculate were first recorded at 4.5 months of age in three kids and presence of matured, motile cells with more than 500 x 10⁶/ml sperm concentration was recorded in all the kids from 6 months of age onwards. Ejaculate characters of 76 semen samples collected from the bucks aged between 6 to 12 months are presented in Table 3. Volume of semen ejaculate at 6 months of age was 0.32±0.02 ml, which increased significantly (P<0.01) during 11 to 12 months. Volume of semen ejaculates in the present study were similar to the reports of Furstoss et al., (2009); Sultana et al., (2013) and Kumbhar et al., (2019) in goats, but slightly lower than the observation by Chaudhari et al., (2018) in Surti bucks (0.7 ml) at 12 months of age. The lowest spermatozoa concentration in the semen ejaculates was observed at 6 months of age and the sperm cell concentration increased significantly (P<0.01) over the period and reached to 3176.14±66.4 × 10⁶/ml at 12 months of age. Sperm cell concentration recorded in the present study was in close agreement with Chaudhari et al., (2018), who found 991±20.48 × 10⁶/ml sperm concentration in Surti bucks at 7 months of age. However, the values were higher than those reported by Thakur et al., (2005) in Chegu Pashmina bucks (1759±79.79 × 10⁶/ml), Gogoi et al., (2008) in Beetal × Assam local (2751±102.40 × 10⁶/ml). Kabiraj et al., (2011) opined that older bucks have more spermatogenic activity due to larger testicular size. Environmental factors like nutrition, seasonal changes, semen collection method and collection frequency can influence the activity of accessory sex glands and subsequently semen quality and quantity. According to Aguiar et al., (2006), such increase in the spermatogenic activity results from the significant development of the seminiferous tubules and Sertoli cell differentiation.


       
Mass motility of neat semen ranged from 2.64±0.13 at 6 months of age to 3.71±0.18 at 12 months. There was a gradual increase in the mass motility from 9 months onwards and a significant (P<0.01) difference in mass motility has been observed between the ejaculates harvested during 6 to 7 months and 10 to 12 months. The results of the study are in agreement with Kumbhar et al., (2019) who observed mass motility of 3.78±0.10, the highest value at 9.5 months of age. However, the value of the present study was lower (4.0±0.16) than the observations of Kerketta et al., (2014) in goats found in the Rohilkhand region. Sperm motility is also affected by collection interval as because prolonged collection interval, spermatozoa in the epididymis degenerate resulting inferior quality semen. The individual motility (%) in fresh semen samples was lowest at 6 months of age (56.79±1.24) which increased significantly over the period and reached to 80.71±1.30% at 12 months of age. The present values were in agreement with the findings of Akpa et al., (2013) who reported 80.00±2.42% initial motility in 11 to 13 months old Red Sokoto bucks, while Gimenez, (2007) reported individual motility of buck semen ranged between 70 and 90%. The percentage of non-eosinophilic live sperm cells in the ejaculates of Bengal bucks varied between 61.36±1.11% and 83.14±1.12% at 6 and 12 months of age, respectively. There was a significant (P<0.01) increase in viable sperm count from 9 months to 11 months of age. A higher percentage of live sperm than the present study was reported in indigenous bucks at 12 months of age by Kumbhar et al., (2019), while the lowest values were reported in crossbred bucks Surti bucks (Jadav et al., 2008) and Boer bucks (Suyadi et al., 2012). Factors like age, feeding and breed had an impact on the sperm quality (Abah et al., 2023).
       
The percentage of HOST positive spermatozoa in the ejaculates were in the range of 59.21±1.73 to 80.71±1.52 during 6 to 12 months of age in Bengal bucks. The population of HOST-positive sperm cells increased significantly (P<0.01) in the ejaculates collected during 10 to 12 months of age than those of 6 to 8 months. The values of HOST-positive sperm count in the study were in accordance with that of Chaudhari et al., (2018) in Surti bucks at 7 to 12 months of age. However, lower values were reported by Kale and Tomar (2000) in crossbred bucks and Deori et al., (2016) in Assam Hill goats. Intact acrosome percentage was 57.57±1.21 at 6 months of age, which increased significantly (p<0.01) to 87.57±1.34 at 12 months of age. Dorado et al., (2009); Ahmad et al., (2014) and Deori et al., (2016) reported a higher percentage of intact acrosome than the present study. The abnormal sperm count (%) showed a reverse trend with a significantly (P<0.01) lower value of 9.22±0.4 from 9 months of age onwards. The values of the study were similar to Mahal et al., (2013) who recorded a normal sperm percentage of 87.20±0.66 in 7 to 9 months and 89.20±0.44 in the bucks aged 9 to 12 months. The percentage of abnormal sperm is negatively correlated with age in the present study similar to that of Zamiri and Heidari (2006). Nutritional status, seasonal changes, false mounting, methods of semen collection and collection frequency may influence semen quality in terms of volume, sperm cell concentration and motility parameters.

Based on the findings, such as presence sperm cells in the ejaculate and the in vitro sperm characters at different months of age, it can be concluded that Black Bengal bucks attain puberty and sexual maturity at least by 6 and 12 months of age, respectively and the testicular biometrical measurements increased significantly with advancement of age and body weight.

All authors declare that there is no conflict of interest.