Heritability of Testicular Size and Consistency in Holstein Bulls

Abstract

During the period 1967 to 1973, 4,275 measurements of scrotal circumference and 3,859 measurements of testicular consistency were made on 1,521 Holstein sires in seven bull studs providing artificial insemination service. Heritability of scrotal circumference (a predictor of total sperm output), and three similar measures of testicular consistency as predictors of semen quality and fertilizing capacity were estimated from paternal half-sib correlations. These measurements were corrected for fixed effects of year-season and age of bull within 11 6-month age groupings on bulls ranging in age from 6 to 72 months. Heritability estimates, weighted according to the number of observations per group, averaged .67 for scrotal circumference, .30 and .22 for consistency measured with the weak and strong spring tonometers and .34 for the average of both tonometers. With these heritabilities, high repeatability, ease of taking the necessary measurements, their relationship to reproductive performance of bulls and the current low reproductive rates, it would seem desirable to place some emphasis on these traits in bull evaluation.