The significance of the cytoplasmic droplet in the disintegration of semen in Guernsey bulls

Abstract

The occurrence of sperm disintegration in Guernsey bulls in South Africa was investigated in thirteen animals that were either sterile or displayed low fertility. One of these was kept under observation and subjected to repeated tests and examinations for three years. In an attempt to elucidate the mechanism whereby the sperm head was detached from the tail, the sperm activity in the epididymis, and particularly the discarding of the cytoplasmic droplet, were studied in three normal bulls and two normal rams. In ten affected bulls the percentage disintegrated sperm varied from 4 to 100. In several this percentage was not as high as that reported in Britain and the animals showed some degree of fertility in the early stages, but the condition deteriorated with ageing. Two exhaustion tests were carried out on one bull. These yielded 22 and 25 ejaculates in 85 and 262 minutes totalling 74·7 and 61·7 ml semen respectively. In each test only four intact sperm were found. The tests further showed that spermatogenesis was normal as regards the number of sperm formed, while pH and the citric acid and fructose levels were also normal in the seminal plasma. A determination of fructolysis activity and pH shift showed that the metabolic rate of disintegrated sperm was similar, or only slightly below that of normal sperm. Their survival rate indicated that there was no selective absorption or phagocytosis of either heads or tails in the male genital tract. On centrifugation of semen the biggest concentration of heads was in the sediment and tails predominated in the supernatant fluid. The tails of the sperm are mainly responsible for fructolysis. In the bull available for post mortem study, an examination of sperm from different sites showed that disintegration occurred mainly in the rete testis and curvature of the caput epididymis. Examination of live sperm from different parts of the caput epididymis immediately after collection disclosed considerable activity characterized by violent lashing of the tails in all the spermatozoa with a cytoplasmic droplet. This activity ceased as soon as the droplet was discarded. Most of the droplets are unloaded from the distal end of the middle-piece and few reach the tail. The discarding of the droplets occurs mainly in the curvature of the caput epididymis. It is concluded that in those animals with an abnormally weak attachment between the sperm head and tail, caused by congenital defect or a pathological condition, separation between the two components occurs in the rete testis and caput epididymis during the severe lashing movements made by the sperm in its efforts to cast off the cytoplasmic droplet. The evidence indicates that in affected Guernsey bulls the defect is attributable to a recessive hereditary factor.