Reproductive parameters of pasture-raised Nelore bulls (Bos taurus indicus) in different age

Abstract

This study aimed to demonstrate the effect of age on bull traits such as scrotal circumference, pelage color, and semen quality, from puberty to post sexual maturity. Data from 6607 breeding soundness examinations of pasture raised Nelore bulls were used. The animals presented different age groups ranging from 12 to 80 months. The andrological examination consisted in reproductive clinical evaluation, assessment of scrotal perimeter (PE). In addition, color of pelage (COR; 1-4) was recorded for each animal. Four age groups were established, which were compared by Bonferroni test. Semen parameters, scrotal circumference (PE) and color of the pelage (COR) varied (P < 0.05) according to the age range: A) 12-18m: COR=1.45±0.64a, PE=31.63±3.51cma, Total Motility (Mot)=67.73±17.99%a, Total os sperm defects (TDE)=16.22±16.95%a; B) 18-24m: COR=1.50±0.57b, PE=32.00±3.47cma, Mot=69.60±29.13%a, TDE=14.49±15.00%b; C) 24-36m: COR=1.51±0.66b, PE=33.56±3.91cmb, Mot=69.46±15.52%a, TDE=12.29±12.92%c; D) 36-48m: COR=1.60±0.57c, PE=36.66±3.50cmc, Mot=71.04±16.19%b, TDE=10.87±12.97%d; E) > 48m: COR=1.64±0.72c, PE=38.00±3.22d, Mot=71.54±15.30b, TDE=9.70±16.95d. It was concluded that age influences testicular size, pelage color, and semen quality parameters. As the age progresses, there is an increase in scrotal perimeter, hair darkening, sperm motility and vigor, and reduction of sperm morphological defects of pasture raised Nelore bulls, assessed as from as 12 months of age.