Research Article: A Comparative Study of Fresh and Frozen‐Thawed Semen Quality in Relation to Fertility of Black Bengal Goats

Bangladesh possesses a tropical goat breed popularly known as Black Bengal goat. They are dwarf in size and noted to be famous for their adaptability, fertility, prolificacy, delicacy of meat and superior skin quality (Husain et al. 1996). It is well adapted to hot and humid climate and usually produces twins and triplets. However, it has been observed that there exists sizeable genetic variation with the traits between individuals within and between locations (Amin et al. 2000). These variations can be exploited for genetic improvement using selective breeding within the breed (Husain et al. 1996; Akhter et al. 2000). But it is a matter of great concern that unlike cattle, goat raisers castrate almost all of their male kids at their early age. Consequently, availability of breeding bucks become squeezed day by day (Amin, 1999). Therefore, provision of Artificial Insemination (AI) using selected buck semen is the easiest Semen from six adult male Black Bengal goats (Capra hircus) was collected to compare the fresh and frozen-thawed semen quality and investigate its relationship with the fertility. Each collected samples was divided into two parts: One part of semen was used as fresh and another part was filled into 0.50 ml straws, sealed, cooled (5 ̊C) and equilibrated for freezing. In both cases, semen was diluted with commercial Triladyl diluent (a Tris based diluter). The motility and morphology of fresh and frozen-thawed semen was subjectively evaluated by one operator. It was revealed that motility and sperm abnormality of the frozen semen differed significantly (P<0.05), but differed insignificantly in fresh semen between males. Besides these, fresh and frozen-thawed sperm motilities also differed significantly (P<0.01) between males which varied from 70.83±1.54 to 74.23±1.59% and 44.17±2.39 to 52.31±1.08%, respectively. A significantly (P<0.01) higher sperm abnormalities was observed in frozen-thawed semen (11.18±0.42 to 16.55±0.09%) than that of fresh semen (8.82±0.24 to 9.71±0.52%). Cervical inseminations were performed with fresh and frozen-thawed semen in 997 and 1004 female goats, respectively, both at Nucleus Breeding Flock (NBF) and four project areas. Fresh semen showed significantly (P<0.01) higher kidding rates (59.8%) than that with frozen-thawed semen (43.9%). The motilities of fresh and frozen-thawed semen were positively correlated (0.526 and 0.987; P<0.01), whereas the proportion of morphologically abnormal spermatozoa was negatively correlated (-0.530 and -0.776) with fertility of Black Bengal goats. Males with a higher motility and lower proportion of abnormal spermatozoa provided better fertility.