Cytological characteristics and fertilizing capacity of bull spermatozoa

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Abstract
1. Two methods were used to estimate the frequencies of nine morphological classes of spermatozoa in 257 ejaculates from one Guernsey, five Friesian and seven Hereford bulls at an insemination centre. In nigrosin-eosin stained preparations and in fixed wet preparations the respective mean frequencies (%) were: malformed heads, 1·08 and 0·98; malformed middle pieces, 0·88 and 0·89; bent tails, 3·92 and 4·56; coiled tails, 0·60 and 0·43; free heads, 3·72 and 2·63; free tails, 1·79 and 1·85; neck beads, 0·87 and 0·93; middle-piece beads, 4·91 and 6·83. 2. There were close correlations between the two sets of measurements, but the differences of means were significant for free heads, bent tails, coiled tails, neck beads and middle-piece beads. 3. The mean percentage of dead (eosinophil) spermatozoa was 21·0. 4. The variations in the frequencies of each morphological class and of dead spermatozoa were divided within and between samples, ejaculates, bulls and breeds. The frequencies of all classes differed significantly between ejaculates within bulls; all but broken necks differed between bulls within breeds, and the Friesian and Hereford bulls differed in the frequencies of malformed heads, free heads, malformed middle pieces, free tails, neck beads and dead spermatozoa. The frequencies of bent tails, coiled tails and dead spermatozoa declined significantly with order of ejaculate. 5. The interrelationships of the frequencies of each class were examined. Two new methods used to measure the dead-sperm content of semen were shown to give results significantly correlated with those obtained by the conventional staining method and with motility ratings. 6. The interrelationships of measurements of the individual characteristics and conception rate were examined. Within-bull variations in conception rate showed a significant positive correlation (P < 0·05) with the frequencies of malformed heads and free heads. The between bull variation in conception rate showed a negative correlation with the frequency of neck beads (P < 0·05).