Testicle size as indicator of fertility in bulls

Abstract

Male calves from the high value parents, bull fathers and bull dams, enter the selection for artificial insemination. After laboratory tests, the calves are taken to the center for artificial insemination, and after a stay in quarantine the are moved to a test station. At the age of twelve months they are measured for assessing the value of each calf exterior. One of the measures recorded was the testicle scope. On the basis of testicle size, it is possible to predict sperm production potential. For the determination of testicle size (testicular biometry), tapes or rulers were used. The aim of this work was to investigate the possible effect of testicle size on sperm production in young bulls used for artificial insemination. For that purpose there were used the data on circumference of testicles of one year old bulls just starting production of sperm, and then compared with certain semen quality parameters such as: volume of ejaculate and concentration and percentage of alive and progressively mobile spermatozoa. The investigation included all young bulls that started production in the period from 2010. to 2012., that is 36 bulls of various breeds (Simmental, Holstein Friesian, Montafon). After the testicle scope measuring in these bulls, there were observed the parameters of the sperm quality during the following one year period. The obtained results showed that the increased testicle size was followed by the increased average ejaculate quantity, in other words: 3.7 ml in group of bulls with testicle circumference below 30 cm, to 6.7 ml in bulls whose testicle circumference was over 40 cm. Also, the results showed that there was a correlation between the increased testicle size and the increased spermatozoa concentration. The values grow to testicle scope of 36 cm, and above that they were still high but with some oscillations. When it came to relation between testicle scope and the percentage of alive and progressively mobile spermatozoa, the trend line showed their positive correlation. The percentage of rejected ejaculates varied from 72% in bulls wit testicle scope below 30 cm to 10% in bulls with testicle scope above 35 cm. On the basis of the results obtained in this work, the conclusion is that testicle size is an indicator of bull fertility; that there is a significant correlation between testicle size and ejaculate volume, and that there is a need to explore a genetic link between testicle size and the fertility of their daughters.