Testicular biometric traits and seminal plasma biochemical markers as indicators of semen quality in Barbari bucks

Introduction

Goat farming plays a significant role in the livelihood of rural households and contributes substantially to meat, milk, skin, and fibre production. Among indigenous goat breeds, Barbari goats are valued for their adaptability, prolificacy, and reproductive efficiency. Efficient reproductive performance of breeding bucks is essential for genetic improvement and enhanced productivity in goat production systems, as a single male can influence the reproductive success of numerous females (Katz, 2007; Ngoma et al., 2016) [12,18] . Evaluation of male reproductive potential is a key component of breeding soundness assessment. Testicular biometric traits such as scrotal circumference, testicular length, width, thickness, and volume are widely recognized as reliable indicators of reproductive capacity and semen production in breeding males (Pant et al., 2003; Elmaz et al., 2008) [8,19] . Testicular size has been reported to be positively associated with body growth and spermproducing ability, while scrotal circumference serves as an important predictor of testicular function and fertility (Ridler et al., 2012; Maroto-Morales et al., 2016) [16,22] . Seminal plasma plays a crucial role in sperm metabolism, transport, protection, and fertilization. It contains a complex mixture of proteins, lipids, minerals, and other biochemical constituents secreted by the testes, epididymis, and accessory sex glands (Mann and Lutwak-Mann, 1981) [15] . Biochemical markers such as albumin, total protein, cholesterol, triglycerides, sodium, potassium, chloride, calcium, and phosphorus are involved in maintaining sperm viability, motility, membrane integrity, and fertilizing ability (Abdel-Rahman et al., 2000; Juyena and Stelletta, 2012) [1,10] . Previous studies have demonstrated associations between seminal plasma biochemical constituents and semen quality traits, indicating their importance in assessing reproductive performance (Arruda-Alencra et al., 2012; Umar et al., 2018) [3,24] . Despite the recognized importance of testicular measurements and seminal plasma composition, information regarding their interrelationship in Barbari bucks remains limited. Understanding the association between testicular biometric characteristics and seminal plasma biochemical markers may provide valuable insights for the selection of superior breeding males and improvement of reproductive efficiency. Therefore, the present study was undertaken to evaluate the correlation between testicular biometric traits and seminal plasma biochemical markers in Barbari bucks.

Materials and Methods Experimental Animals and Management

The study was conducted at the Buck Semen Analytical Unit, Goat Farm, Department of Veterinary Physiology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura, Uttar Pradesh, India, during 2023-2024. Fifteen healthy Barbari bucks aged between 1.5 and 2 years, weighing 25-30 kg, were selected for the study. All animals were maintained under a semi-intensive management system and fed according to standard farm practices.

Testicular Biometry

Testicular biometric measurements were recorded one day prior to semen collection. Scrotal circumference (cm) was measured at the widest diameter of the scrotum using a flexible measuring tape following the procedure described by Ball et al. (1983) [5] (Fig 1). The testes were gently positioned at the bottom of the scrotum, and the circumference was measured around the greatest diameter of the scrotum. Testicular length, width, and thickness (cm) were measured using a Vernier calliper as described by Raji et al. (2008) [21] . Testicular volume (cm³) was calculated according to the formula proposed by Bailey et al. (1998) [4] . (Fig 2)

Testicular Volume = 0.5236 × Testicular Length × (Testicular Width)² Repeated measurements were taken for each animal, and the mean values were used for statistical analysis.

Semen Collection and Seminal Plasma Separation

Semen samples were collected twice weekly from each buck using an artificial vagina maintained at 40-42 °C. Four ejaculates were collected from each buck during the study period. Following collection, semen samples were centrifuged, and the seminal plasma was separated and stored at -20 °C until biochemical analysis.

Analysis of Seminal Plasma Biochemical Markers

Seminal plasma samples were analyzed for albumin, total protein, cholesterol, triglycerides, sodium, potassium, chloride, calcium, and inorganic phosphorus using commercially available diagnostic kits and standard spectrophotometric procedures. Biochemical analyses were performed according to the manufacturer's protocols using a semi-automated clinical chemistry analyser (IngeniIous AUTOCHEM) (Fig 3).

Statistical Analysis

Data were expressed as mean ± standard error of mean (SEM). Pearson's correlation coefficient was used to determine the relationship between testicular biometric traits and seminal plasma biochemical markers. Statistical analyses were performed using SPSS software (IBM Corp., 2021) [9] , and significance was considered at p<0.05.

Result and Discussion

The correlation coefficients among testicular biometric traits and seminal attributes are presented in Table 1. In Group I bucks (SC: 20-25 cm), scrotal circumference exhibited a moderate positive correlation with sperm viability (r = 0.619), indicating that bucks possessing larger scrotal circumference tended to have a higher proportion of viable spermatozoa. Semen volume was positively associated with testicular width (r = 0.503), whereas mass motility showed a positive correlation with testicular length (r = 0.629). Conversely, testicular thickness (r = -0.774) and testicular volume (r = -0.698) were negatively associated with sperm viability. In Group II bucks (SC: >25-31 cm), testicular volume exhibited a significant positive correlation with mass motility (r = 0.674; p<0.05), while the remaining testicular biometric traits showed weak to moderate relationships with seminal characteristics. The positive relationship observed between testicular measurements and seminal traits highlights the importance of testicular development in determining reproductive efficiency. Testicular size is directly related to the amount of seminiferous epithelium present within the testes and consequently influences sperm production capacity. Scrotal circumference is widely recognized as one of the most reliable and easily measurable indicators of testicular function and sperm-producing ability. Bucks possessing larger testes generally have greater spermatogenic tissue mass, resulting in enhanced sperm production and superior semen quality. Similar observations have been reported by Kabiraj et al. (2011) [11] , who found significant positive associations between scrotal circumference, testicular dimensions and semen quality traits in Black Bengal bucks. Bongso et al. (1982) [26] also reported positive relationships between scrotal dimensions and sperm output. Kumbhar et al. (2019) [13] observed that testicular length, testicular width and scrotal circumference were positively associated with sperm concentration, live sperm count and mass activity in Osmanabadi bucks. More recently, Alam et al. (2024) [2] and Samir et al. (2024) [23] reported significant relationships between testicular biometry and semen quality parameters in goat bucks, suggesting that testicular measurements can be effectively used as indicators of breeding soundness and reproductive performance. The significant positive association between testicular volume and mass motility observed in the present study further supports the hypothesis that larger testes contribute to improved sperm production and sperm functionality. The correlations between seminal plasma biochemical constituents (albumin, total protein, cholesterol and triglycerides) and seminal attributes are presented in Table 2. In Group I bucks, albumin exhibited a moderate positive correlation with semen volume (r = 0.426), whereas cholesterol showed positive associations with sperm concentration (r = 0.326) and sperm viability (r = 0.254). Total protein and triglycerides displayed weak relationships with most seminal attributes. Similarly, in Group II bucks, albumin, total protein, cholesterol and triglycerides demonstrated weak to moderate correlations with semen volume, mass motility, sperm concentration and sperm viability. None of these associations were statistically significant. Seminal plasma proteins are known to play essential roles in sperm metabolism, transport, capacitation, membrane stabilization and fertilization. Albumin acts as an antioxidant and membrane-protective molecule that helps maintain sperm viability during storage and transport through the female reproductive tract. Total protein concentration in seminal plasma reflects secretory activity of the accessory sex glands and contributes to sperm nourishment and protection. Cholesterol is a major constituent of the sperm plasma membrane and regulates membrane fluidity, stability and capacitation processes. Triglycerides serve as an indirect source of energy for sperm metabolism. Therefore, even though correlations observed in the present study were weak to moderate, these biochemical constituents remain physiologically important for maintaining sperm functionality. The findings of the present study are in agreement with Umar et al. (2018) [24] , who reported positive associations between seminal plasma biochemical constituents and semen quality in Teddy goat bucks. Malik et al. (2018) [14] also reported relationships between biochemical constituents of seminal plasma and physical characteristics of Damani buck semen. Arruda-Alencar et al. (2012) [3] emphasized the importance of seminal plasma proteins in regulating sperm function and fertility, while Caballero et al. (2012) [7] described seminal plasma proteins as important modulators of sperm function and reproductive performance. Similarly, Juyena and Stelletta (2012) [10] reported that seminal plasma proteins contribute significantly to sperm membrane integrity and sperm survival. The absence of strong correlations in the present investigation may indicate that seminal plasma protein fractions influence sperm quality through complex biochemical interactions rather than direct linear relationships. The correlation coefficients between seminal plasma mineral constituents and seminal attributes are presented in Table 3. In Group I bucks, sodium exhibited a significant positive correlation with mass motility (r = 0.465; p<0.05), while chloride showed a highly significant positive correlation with sperm concentration (r = 0.717; p<0.01). Potassium displayed a negative association with sperm viability (r = -0.394), whereas phosphorus showed a moderate positive correlation with sperm concentration (r = 0.331). Calcium exhibited weak positive correlations with semen volume and sperm concentration. In Group II bucks, potassium demonstrated a highly significant negative correlation with semen volume (r = -0.456; p<0.01) and a significant negative correlation with sperm concentration (r = -0.317; p<0.05). Sodium showed weak positive associations with all seminal characteristics, while chloride, calcium and phosphorus exhibited weak correlations with semen volume, mass motility, sperm concentration and sperm viability. Mineral constituents of seminal plasma are indispensable for maintaining sperm metabolism, membrane integrity, osmotic balance and fertilizing capacity. Sodium and potassium ions are involved in regulating membrane potential and ion transport mechanisms that influence sperm motility. Calcium is particularly important for sperm capacitation, hyperactivation and acrosome reaction, whereas phosphorus contributes to cellular energy metabolism through ATP production. Chloride ions play a significant role in maintaining osmotic equilibrium and membrane stability within sperm cells. The positive association between sodium concentration and mass motility observed in the present study is consistent with the findings of Umar et al. (2018) [24] , who reported favourable relationships between seminal plasma mineral constituents and sperm motility in Teddy goat bucks. Similar observations were reported by Pesch et al. (2006) [20] , who demonstrated significant associations between seminal plasma macro-mineral concentrations and semen quality traits. Massanyi et al. (2008) [17] also observed relationships between seminal plasma electrolytes and sperm characteristics. Abdel-Rahman et al. (2000) [1] reported that potassium and calcium concentrations were positively associated with sperm viability and several seminal characteristics, emphasizing the importance of mineral balance for optimal sperm function. Furthermore, Mann and Lutwak-Mann (1981) [15] described seminal plasma minerals as essential regulators of sperm physiology and fertilization potential. The highly significant positive association between chloride concentration and sperm concentration observed in Group I bucks suggests that chloride ions may contribute to maintaining an optimal environment for sperm production and survival. On the other hand, the significant negative relationship of potassium with semen volume and sperm concentration in Group II bucks may indicate that elevated potassium concentrations could adversely affect certain seminal characteristics. Similar variability in potassium associations has been reported previously by Abdel-Rahman et al. (2000) [1] , Pesch et al. (2006) [20] and Massanyi et al. (2008) [17] , and may be influenced by breed differences, physiological status, nutritional factors and secretory activity of the accessory reproductive glands. The present investigation demonstrates that testicular biometry and seminal plasma biochemical composition are closely associated with reproductive performance in Barbari bucks. Among the testicular measurements, testicular volume emerged as the most important parameter due to its significant positive relationship with mass motility. Among seminal plasma constituents, sodium and chloride showed favourable associations with semen quality traits, whereas excessive potassium concentration was negatively associated with semen volume and sperm concentration. These findings suggest that testicular biometric traits together with seminal plasma biochemical markers can serve as useful indicators of breeding soundness and reproductive potential in Barbari bucks. Therefore, their incorporation into routine breeding soundness evaluation programmes may assist in the identification and selection of superior breeding males for genetic improvement and enhanced reproductive efficiency.

Conclusion

The present study demonstrated that testicular biometric traits and seminal plasma biochemical constituents are closely associated with semen quality in Barbari bucks. Among the biometric parameters, testicular volume emerged as the most reliable indicator of reproductive performance owing to its significant positive association with mass motility. Sodium and chloride concentrations showed favourable relationships with key seminal attributes, whereas elevated potassium levels were negatively associated with semen volume and sperm concentration. These findings highlight the potential of integrating testicular biometry and seminal plasma biochemical profiling into breeding soundness evaluation programmes for the identification and selection of superior breeding bucks, thereby contributing to enhanced reproductive efficiency and genetic improvement in goat production systems.

Acknowledgement

AcknowledgementsThe authors express their sincere gratitude to the faculty and technical staff of the College of Veterinary Science and Animal Husbandry, U.P. Pandit Deendayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan (DUVASU), Mathura, Uttar Pradesh, India, for providing the facilities and support required to carry out this research.

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