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A.R.C. Unit of Reproductive Physiology and Biochemistry, University of Cambridge, U.K. A defect of the sperm acrosome, called 'knobbing' has been associated with sterility in the bull (Teunissen, 1946; Blom, 1948; Hancock, 1952; Donald & Hancock, 1953; Blom & Birch-Andersen, 1962; Blom, 1972), and boar (Bane, 1961), and has been seen in stallion (Dott, 1975), ram, dog and impala (unpublished). Donald & Hancock (1953) came to the conclusion that this was an autosomal sex-linked recessive characteristic in Friesian bulls. At the level of the light microscope it is seen as an apical, often eccentric swelling which folds back over the head. Blom & Birch-Andersen (1962) described this character as a swelling of the apical body to six to eight times normal. Much of the region was cystic and contained vesicles with inclusions. The ultrastructure of this defect in Friesian bulls is described in the present paper. Semen was collected in
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Cran et al. (1976) studied this question.
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