Measurement of Testicular Size and its Relation to Production of Spermatozoa by Bulls

Abstract

A correlation of 0.94 was obtained between scrotal circumferences in situ and volumes or weights of excised testes of 69 bulls. Measuring testicular length in situ did not increase the correlation. Low correlations of 0.43 and 0.32 were found between scrotal circumferences and numbers of spermatozoa produced by bulls in routine service in bull studs. In exhaustion tests, there was a correlation of 0.92 between scrotal circumferences and spermatozoa produced with 16 young bulls, and with 6 aged bulls, -0.53. Nine young bulls averaged 48.5 x 106 spermatozoa per gram of testicular tissue per week the first year; 7 of these bulls, 63.4 x 106 a year later; and the 6 aged bulls, 46.7 x 106. In 3 studies on the relationship of testicular size to body size of mature bulls, the correlation was too low to permit estimation of one by the other. Averages, ranges, and 5% confidence limits by breeds are given for scrotal circumferences of 361 bulls representing 7 breeds in 6 artificial breeding organizations.