Durchflusszytometrische Verfahren zur Beurteilung der Spermaqualitat nach einer experimentell induzierten Hyperthermie am Bullenhoden

Field: Veterinary (Health Sciences)

The aim of this study was to examine if the assessments of sperm quality can be better objectified and standardized by using flow cytometric examinations. For this investigation temporary deterioration of sperm quality was induced by a local heating of testes in bulls. The scrotal surface temperature of 4 bulls was increased during the local heating of testis by enclosing the entire scrotum for 48 hours by 6.4°C to 7.1°C. Semen was collected 3 times a week from Day -7 to Day 61 and once a week from Day 68 to Day 83 (Day 0 = the day of scrotal insulation). Each ejaculate was conventionally examined (numbers of total spermatozoa, sperm concentration, morphology and proportion of vital spermatozoa after staining with bromphenol blue nigrosin). The percentage of motile spermatozoa and progressive motile spermatozoa of motile sperm were determined with a computer-assisted motility analysis. Using flow cytometry the proportions of sperm with the following parameters were examined and analyzed: intact plasma membranes after staining with SYBR®14/PI, high mitochondrial membrane potentials after staining with JC1, damaged acrosome status after staining with FITC-PNA/SYTO®17/PI, and sperm with defective chromatin structure or rather with high DNA fragmentation index (DFI) by SCSA. The deterioration of sperm quality after elevating testicular temperature was correspondent to a large extent to the typical changes of the conventional sperm parameters, which result is in agreement with previous similar studies. After testicular hyperthermia (Day 0) changes of sperm quality occurred in the following sequence. There was a notable increase in secondary sperm abnormalities as well as a decrease in sperm motility on Day 9 after testicular hyperthermia. The proportions of vital spermatozoa after staining with bromphenol blue nigrosin, total sperm count and sperm concentration were decreased on Day 12 for the first time. At the same time the primary sperm abnormalities began to increase. The primary abnormalities most frequently encountered were morphological head defects of spermatozoa. Concurrent with the changes specified above the following alterations of sperm parameters were observed with flow cytometry. Beginning on Day 7 after testicular hyperthermia sperm with defective acrosome status increased. From Day 9 on sperm with intact plasma membranes and sperm with high mitochondrial membrane potentials began to decrease. On Day 12 after testicular hyperthermia the proportion of sperm with defective chromatin structure (spermatozoa with high DFI) started to increase significantly. The relationships between the proportions of defective sperm chromatin structure assessed with the SCSATM test and the proportions of sperm head defects were highly significant (r = 0.81; P < 0.0001). The proportion of sperm with a high mitochondrial membrane potential correlated positively to the sperm motility (r = 0.83; P < 0.0001). Significant correlations between the viability assessed by light microscopy and the percentages of spermatozoa with intact plasma membrane obtained by flow cytometry (r = 0.77; P < 0.0001) occurred. The increase of the proportion of the sperm with defective chromatin structure (spermatozoa with high DFI) was more clearly pronounced than that of the morphological abnormal sperm heads. This result indicates that heat stress had led to chromosome defects not only in morphologically abnormal but also in normally appearing sperm cells. In addition, morphological sperm abnormalities, especially sperm head defects, may be indicative of chromosome abnormalities also in normally appearing sperm cells of an ejaculate. This study shows that flow cytometric assessments of the ejaculate is a reliable and objective method in semen investigation. It provides additional important information about the sperm quality. In further studies, it has to be clarified, whether the prospective fertilization capacity from an ejaculate and/or the fertility of a bull can be predicted with this method more reliable than with the conventional sperm evaluation.