GENETIC AND ENVIRONMENTAL-FACTORS AFFECTI NG SEMEN QUALITY OF YOUNG HOLSTEIN BULLS

Semen traits were measured from 294 young Holstein bulls between the a ges of 10 and 18 mo. Bulls were sampled between the years 1987 and 198 9 and the first four suitable ejaculates from each bull were retained for study. The season of the year, the year and the sire of each bull were used as factors and the age of the bulls and the inbreeding coeff icient were used as co-factors for the analyses of variance and covari ance. The sire effect was declared significant for the volume (P < 0.0 01), concentration (P < 0.05) and the number of motile spermatozoa per ejaculate (P < 0.001). Intraclass regression studies indicated that e ach increase of 1 d of age in young bulls increased the volume of the ejaculate by 0.004 mt, the concentration and the motility of the ejacu late by 0.024 x 10(8) spermatozoa mL(-1) and 0.034% and the number of motile spermatozoa by 0.091 x 10(8) per ejaculate. A 1% increase in th e inbreeding coefficient (F) decreased the motility of spermatozoa by 0.30% and the concentration of the ejaculate by 0.14 x 10(8) mt, resul ting in a decreased total number of inseminations possible by 13.83 do ses. It also increased the number of rejected samples by 0.25 and dela yed sexual maturity by 3 d. Heritability estimates of semen traits var ied from 0.25 and 0.79. The genetic and phenotipic correlations were r espectively -0.72 and -0.47 for the correlations between volume and co ncentration, 0.140 and 0.07 between volume and motility and -0.22 and -0.01 between motility and concentration.