The experimental bucks were maintained in the nucleus breeding flock (NBF) of the research project entitled “Conservation of Black Bengal goat as the Potential Genetic Resource in Bangladesh” at AI centre, Bangladesh Agricultural University, Mymensingh-2202.
Animals used Twelve black Bengal bucks aged between 6 to 36 months were selected on the basis of morphometric characterization and the potentiality to produce quality semen. The selected bucks were again divided into three different age groups as A (0.5 to 1.0 years), B (1.5 to 2.0 years) and C (2.5 to 3.0 years).
Feeding and other managemental procedures The bucks were fed with Napier and/or German grass twice daily as per requirement. The feed was supplemented with commercial concentrate (crude protein content: l20 g/kg DM and energy content: 10.4 MJ ME/kg DM) in the morning and again in the afternoon at the rate of 100 gm/ buck of 20 kg live weight. The breeding bucks were also supplied with germinated gram (20 gm/buck/day). Clean and safe water was made available at all times. Throughout this study, the nutrition of bucks remained uniform and constant. All bucks were vaccinated against Peste des Petits Ruminants (PPR) and dewormed routinely with Ivermectin ® thrice a year. The individual pen was provided for each buck (10 sq ft) in the shed with the provision of sufficient access to fresh air and their movement freely and they were allowed to graze outside for one hour daily.
Semen collection The bucks were trained to ejaculate in the artificial vagina (AV). Semen was collected within 8.30 AM twice a week from each buck after cleaning the prepuce with antiseptic (savlon) solution. Collection of semen was done with artificial vagina maintaining optimum pressure and temperature about 41 to 43°C. The bucks received homosexual stimulation by being exposed to the teaser male. The semen was collected twice a week for up to 45 days thus 12 records were made available for this study.
Evaluation of semen Immediately after collection the volume of each ejaculate was measured directly from the reading of the graduated collection vial in millimeters. Then semen samples were prepared according to the method described by Herman and Madden (1963) and the concentration of spermatozoa per ml of semen was counted by hemocytometer method and expressed as billion per ml. The following formula was used for calculating the total number of spermatozoa per ml of fresh semen.
Total number of spermatozoa per ml of semen = [{(C×400)/S}×D] ×10 -3
Where C = Number of sperm counted in a given number of small squares. S = Number of small squares counted. D = Dilution ratio
Eosin-nigrosin staining method has been used as routine staining in order to evaluate sperm viability (World Health Organization, 1992), briefly, after washing sperm samples in saline solution at 37°C, one drop of the suspension containing 35 x 10 6 sperm/ml was placed on a tempered glass slide, which was mixed with one drop of Eosin-nigrosin solution. The mixture was smeared on the glass slide and let air-dry. The samples were observed under a light microscope. Eosin penetrated in non-viable cells which appear red. Nigrosine offers a dark background facilitating the detection of viable, nonstained cells. Four smears were performed from each ejaculate, in fresh samples. A total of 333 sperms were counted randomly from different fields of the slide. The number of dead spermatozoa deducted from the total number of spermatozoa gave the number of live spermatozoa and expressed in percentage.
Measurement of body weight The body weight of each buck was recorded in kg in the morning before the animals were slaughtered. The weights were taken with a top-loading balance.
Measurement of scrotal circumference The scrotal circumference was measured as per the method recommended by the Society of Theriogenology (Ball et al., 1983). The testes were first retracted into the lower part of the scrotum for the measurement of scrotal circumference. To prevent the separation of the two testes, the thumb and the fingers were placed on the sides rather than on the front or back of the scrotum. Then a flexible metal tape (Scrotal tape; Lane Manufacturing, Co., Denver, USA) was looped and placed around the greatest diameter of the scrotum and pulled snugly so that the tape was firmly in contact with the entire circumference. Repeated measurement was done and the mean of the measures was recorded to ensure accuracy.
Slaughtering and biometrical study Immediately after slaughter, both the left and right testes were collected from the bucks of three different age groups. Immediately after collection, the length and width of testes were measured by measuring tape and weights were measured in digital balance.
Statistical analysis Simple ANOVA was performed considering the age of buck and to observe the significant differences among the mean values, Duncan’s multiple range test (DMRT) was done. Lastly, correlations among the traits were also performed. Analysis was performed with the help of a statistical analysis system (SAS, 1998).