Abstract
Bull breeding programs use age as a selection criterion. This study explores the effect of Brahman bull age on sperm motility, morphology, morphometrics, and kinematics. The experiment took place on two cattle farms owned by the Costa Rica Institute of Technology. Thirty-one ejaculates were collected via electroejaculation from 13 sexually mature Brahman bulls, classified into groups according to their age (“Adult” > 31 months;” Young” ≤ 31 months). Semen was evaluated for motility, kinematics, morphology and morphometrics with a CASA ISAS®v1 system and concentration was determined using a photometer. The results showed that the sperm of younger bulls (p<0.05) exhibited higher curvilinear velocity (VCL), rectilinear velocity (VSL), and average path velocity (VAP). Sperm linearity (LIN), wobble (WOB), and straightness (STR) were higher in adult than young bulls (p<0.05). Adult bull sperm head parameters were higher than for young bulls (p<0.05). More elliptical and elongate spermatozoa were observed in adult bulls. The sperm mid-piece area was higher in young bulls. The multivariable assessment identifies four clusters, with differences between each group (p<0.05). In conclusion, our results show that age influences the quality of the bovine ejaculate and its potential fertility.