Testicular Development in Holstein, F1 Crossbred Holstein-Gyr, Gyr, and Nellore Bulls During Puberty and Sexual Maturity in Tropical Conditions

Abstract

Context: Puberty and sexual maturity are very important economic aspects in the beef industry and bull production. The aim of this study was to characterize and determine the sexual development of Bos taurus, Bos indicus, and F1 crossbreeds of these two subspecies of bulls and their testicular growth and shape. We observed the evolution of testicular development characteristics and seminal aspects from puberty to sexual maturity in bulls, and we verified differences between seminal characteristics, scrotal circumference, and testicular volume between puberty and sexual maturity. We used 17 Holstein, 21 Gyr, and 29 crossbred F1 Holstein-Gyr bulls from 7 to 25 months of age in a semi-extensive system, as well as 18 Nellore from 10 to 30 months of age in an extensive pasture range. Every four weeks, we measured testicular growth (length, width, and volume) and scrotal circumference. Semen samples were collected every two weeks, and physical and morphological aspects of ejaculate were observed. Seminal puberty and sexual maturity were defined according to seminal characteristics. Age at puberty and sexual maturity differed between Holstein, Gyr, and crossbred F1 Holstein-Gyr bulls. These ages were similar between the Nellore and Gyr zebu bulls. The period from puberty to sexual maturity was similar between the genetic groups in the study. The testicular shape was moderately long in zebus, but ovoid in taurine and F1 crossbred bulls. The relationship between testicular width and length was larger between taurine and F1 crossbred bulls than zebu bulls. Scrotal circumference and testicular volume development were represented by curves logistic functions.  Scrotal circumference as a measure of sexual development at puberty and sexual maturity differed between taurine, crossbreed F1, and zebu bulls. However, at sexual maturity, testicular size in bulls of different zebu and taurine subspecies was equivalent in all dimensions assessed. In addition to scrotal circumference, measurement of testicular length could be included as a means to calculate testicular volume when working with the production of zebu bulls in a tropical climate, as a method of monitoring sexual development.