Testicular cytology indicates differences in Sertoli cell counts between "good freezer" and "poor freezer" bulls

In artificial insemination, poor quality of semen unsuitable for cryopreservation and susceptibility of spermatozoa to cryodamage in crossbred bulls have been a matter of concern. Present study was designed to identify the testicular cytology indices that might be used to predict the semen quality and cryotolerance of spermatozoa in bulls. Based on the ejaculate rejection rate and sperm cryotolerance, bulls (Holstein Friesian X Tharparkar crossbred) were classified into either good (producing good quality semen with spermatozoa having good cryotolerance; n=4) or poor (producing poor quality semen with spermatozoa having poor cryotolerance; n=4). Testicular cytology was studied in all the 8 bulls using fine needle aspiration technique. Testicular cytology of good bulls and poor bulls differed significantly. The proportion of Sertoli cells was significantly higher in good bulls (25.3 +/- 1.6) compared to poor bulls (11.0 +/- 0.8). The Sertoli cell index was 46.1+5.0 in good bulls while it was only 13.8 +/- 1.3 in poor bulls. The cut off values, as determined using Receiver Operating Characteristics analysis, indicate that the bulls having testicular cytogram comprising of <15.5% Sertoli cells, <24.3 Sertoli cell index and >4.0 spermatogenic cells to Sertoli cell ratio might be a poor bull in terms of semen quality and cryotolerance of spermatozoa. The proportion of Sertoli cells in the testicular cytology had positive (P < 0.05) relationship with semen quality and cryotolerance of spermatozoa.