In vitro fertilizing characteristics of bovine sperm with abnormal morphology

Abstract

A combination of in vitro fertilization (IVF) and sperm function tests were used to determine the fertilizing characteristics of bovine sperm with abnormal morphology. Bovine sperm affected with the pyriform defect had a reduced ability to bind to and penetrate zonae pellucidae and although those penetrating oocytes were involved in the fertilization process, the resulting zygotes appeared to have a reduced ability to initiate cleavage. Bovine sperm with the knobbed acrosome defect had a reduced ability to bind to and penetrate the zona pellucida. Knobbed sperm had impaired sperm plasma membrane function which predisposed them to spontaneous acrosome reaction on incubation after thawing, reducing oocyte interaction. The post-zona penetration fertilizing characteristics of normal sperm associated with knobbed sperm also appeared to be impaired. Bovine sperm with multiple nuclear vacuoles had a reduced ability to bind to and penetrate the zona pellucida of bovine oocytes. However, those gaining access to the ooplasm participated normally in fertilization. A proportion of sperm with proximal droplets failed to swim through the sodium hyaluronate swim-up medium and sperm with proximal droplets failed to bind with the zona pellucida of oocytes. Apparently normal sperm co-existing in the semen along with proximal droplets were also functionally deficient, resulting in reduced zonae binding, and those oocytes that were fertilized did not develop beyond the cleavage stage of development. In summary, morphologically abnormal sperm failed during the various steps of the fertilization process depending on the nature of abnormality. However, knobbed sperm, pyriform-shaped sperm, sperm with multiple nuclear vacuoles and sperm with proximal cytoplasmic droplets appeared to have similar functional deficiencies suggesting that abnormal morphology may be a marker of accompanying functional deficiencies. The normal sperm coexisting in the semen along with high proportions of abnormal sperm also appeared to have impaired fertilizing ability suggesting that these sperm may also have structural or functional inadequacies or that the presence of high proportion of abnormal sperm in an ejaculate is a symptom of abnormal spermatogenesis.