Relationship between total protein concentration of seminal plasma and sperm characteristics of highly fertile, fertile and subfertile Barki ram semen collected by electroejaculation

The aim of this study was to determine the relationship between total protein concentration (TPC) of seminal plasma (SP) and semen characteristics in rams. A total of 105 ejaculates from 21 Barki rams, of known fertility (9 highly fertile, 9 fertile and 3 subfertile) were collected by electroejaculation (EE) and used in the present study. An aliquot (200 μl) from each ejaculate was used for evaluation of semen characteristics (wave motion, motility, viability, sperm morphology, intact-acrosome, sperm concentration and total sperm count per ejaculate). The remaining volume was centrifuged to collect SP and TPC (g/dl) of SP was estimated with hand-held Refractometer; then SP proteins were separated on 15% (w/v) polyacrylamide gel. The results revealed that TPC of SP and almost all semen characteristics were significantly (P < 0.05) lower in subfertile (SF) group than both highly fertile (HF) and fertile (F) groups but the longest (85.0 ± 4.1 s) stimulation time (ST) was recorded in SF group. Moreover, TPC of SP in HF and F groups showed highly significant (P < 0.001) negative correlation with ST but showed highly significant positive correlation with all semen characteristics. However, in SF group neither ST nor semen characteristics showed any significant correlation with TPC of SP. Eosin-nigrosin (EN) stain, hypoosmotic swelling test (HOST) and glutaraldehyde fixation (GF) were capable to discriminate among HF, F and SF groups of rams. In total, fourteen protein bands with different molecular weights, ranging from 7 to 91 kDa, were detected on polyacrylamide gel. Protein bands of 11, 13 and 22.5 kDa were more prominent in HF group than F group but it was faint to absent in SF group. Moreover, bands of 91, 80 and 27 kDa were prominent in F and SF groups than HF group. In conclusion, TPC and protein profile of SP were closely correlated with semen characteristics and might be useful tools to determine ram fertility or semen quality. Protein bands of 11, 13 and 22.5 kDa were fertility-associated proteins in Barki rams SP. The effects of these fertility-associated proteins on sperm cell function required further investigation.