Further studies on the nuclear chromatin of morphologically abnormal bull spermatozoa.

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are commonly found in ejaculates from bulls with certain types of reduced fertility. Intranuclear spaces and a granular appearance of the nuclear chromatin were the major abnormalities observed in a high percentage of spermatozoa from two infertile bulls (McCosker, 1969). The organization of the DNA and nuclear proteins forming the deoxyribonucleoprotein complex (DNP) in the chromatin of deformed sperm heads has received little attention. Previous studies have demonstrated that most morphologically abnormal sperm heads contain the same amounts of DNA as their normally shaped counterparts (Gledhill, 1966a). Defects in the binding of nuclear protein to DNA, which probably occur during the process of chromatin aggregation in spermateliosis, have only recently been incriminated in the formation of certain misshapen sperm heads (Gledhill, Dar\l=z%o\ynkiewicz & Ringertz, 1971). Their possible r\l=o^\lein an instance of infertility was noted earlier (Gledhill, Gledhill, Rigler & Ringertz, 1966a). The present communication reports a study which had as its objective to determine if the DNA of abnormally shaped spermatozoa has a sensitivity to thermal denaturation that differs from that of normally shaped spermatozoa. The method used allows the analysis of molecular arrangements of DNA within intact, definable sperm heads. Such information has physiological importance as it relates to current work on the maturation ofnuclear chromatin and could show mechanisms which might be involved in the differentiation of abnormal sperm heads. Nine sexually mature and normally fertile dairy and beef bulls of varying ages (H to 15 years) and breeds were used. Spermatozoa from the testis and from the caput epididymidis were obtained in a manner previously described (Gledhill, 1966b). Spermatozoa were also obtained from the left vas deferens of two of the bulls (courtesy of Dr R. P. Amann, The Pennsylvania State Univers¬ ity) at 1 and 3 days after cannulation by a modification of the method of Amann, Hokanson & Almquist, (1963) and Sexton, Amann & Flipse (1971). Ejaculated spermatozoa were collected with the aid of an artificial vagina. The criteria used for differentiating morphologically abnormal from normal