Sexual development in early- and late-maturing Bos indicus and Bos indicus × Bos taurus crossbred bulls in Brazil

Abstract

Two experiments were conducted to evaluate sexual development in early- and late-maturing Nelore (Bos indicus) and Canchim (3/8 Bos indicus x 5/8 Bos taurus crossbred) bulls and to determine predictors of sexual precocity, and pubertal and maturity status. In Experiment 1, 12 Nelore bulls where examined from 300 to 900 days of age. Puberty was characterized by an ejaculate containing > or =50 million sperm with > or =10% motile sperm, and maturity by an ejaculate containing > or =70% morphologically normal sperm. In Experiment 2, 28 Canchim bulls where examined from 295 to 488 days of age and puberty was characterized by an ejaculate containing > or =30% motile sperm. In both experiments, bulls were classified as early- or late-maturing based on age at puberty. Early-maturing bulls were younger (P < 0.05) than late-maturing bulls at puberty (527 days versus 673 days in Experiment 1 and 360 days versus 461 days in Experiment 2) and at maturity (660 days versus 768 days in Experiment 1). In general, early-maturing bulls were heavier and had greater scrotal circumference (SC), testes, and testicular vascular cone diameter than late-maturing bulls during the experimental period. Scrotal circumference adjusted for 365 days of age was a good predictor of sexual precocity; minimum yearling SC of 19 and 24 cm for Nelore and Canchim bulls, respectively, had the best predictive values. Early-maturing bulls were lighter and had smaller SC at puberty than late-maturing bulls; therefore, sexual precocity was not related to the attainment of a threshold body weight or testicular size earlier, but to lower thresholds in early-maturing bulls. When predictors of pubertal status were evaluated, SC had the best sensitivity/specificity relationship in Nelore bulls, and high sensitivity and specificity in Canchim bulls. When predictors of sexual maturity were evaluated in Nelore bulls, age, weight, and SC had similar sensitivity, specificity, and predictive values. At puberty, approximately 60% of the sperm present in the ejaculate were morphologically defective. Changes in semen quality after puberty in Nelore bulls were characterized by increased motility and proportion of morphologically normal sperm, with a decrease in the proportion of major sperm defects. In conclusion, early-maturing bulls were more developed in the pre-pubertal period and attained puberty at earlier stages of body and testicular development than late-maturing bulls. Yearling SC could be used to select bulls for sexual precocity and SC was the best predictor of pubertal status. Age, weight, and SC were equally good predictors of sexual maturity in B. indicus bulls.

Integrity of the plasma membrane, the acrosomal membrane, and the mitochondrial membrane potential of sperm in Nelore bulls from puberty to sexual maturity

“…The occurrence of intact sperm with a high mitochondrial membrane potential was low, probably because the experiment ended at the early maturation of the bulls, when testes were still in growth phase (Brito et al, 2004). The results suggest that the sperm of Nelore bulls only reaches full mitochondrial membrane potential at the end of sexual maturity, when the bulls become adults.…”

Biometric Study of the Reproductive Organs of Three Breeds of Sheep in Nigeria

“…Keys: 1= paired testes weight; 2= scrotal circumference; 3=paired epididymal weight; 4=mean epididymal length; 5=paired tunica albuginea weight; 6=mean testes volume; 7=mean testes density; 8=caput weight; 9= corpus weight; 10= cauda weight; 11= mean epididymal volume; 12= mean epididymal density; 13= mean testes length. It is particularly important to note that in the evaluation of the breeding soundness of an animal, Brito et al (2004) have reported that heavier testes produce more spermatozoa than the smaller testes. Berdston et al (1987) asserted that a testis, which possesses greater number of Sustentocytes, were heavier and produced more spermatozoa than testes with fewer Sustentocytes.…”

Testis size, peripheral concentrations of testosterone, semen criteria and Sertoli and germ cell numbers in Nelore bulls

“…Previous reports have shown that Nelore bulls attain puberty at ages from 14.8 to 22.1 mo. (TROCÓNIZ et al, 1991;CHASE JÚNIOR et al, 1997;BRITO et al, 2004) and such variation reflects the large genetic diversity of herds, feeding and management strategies existing in Brazil.…”