Scrotal circumference assessment and its relevance as predictor of pubertal phase beginning in Angus yearling bulls.

PRANDO, ALBERTO JOSE; BONAMY, MARTIN; DE IRAOLA, JULIETA JOSEFINA; BALBI, MARIANELA; GIOVAMBATTISTA, GUILLERMO; BALDO, ANDRES

Foz do Iguaçu

Congreso; 54ª Reunião Anual da Sociedade Brasileira de Zootecnia; 2017

Sociedade Brasileira de Zootecnia

Pregnancy rates achieved by yearling bulls (15 months old of age) in natural breeding are similar to thoseobtained by adult breeding males. Reproductive use of yearling bulls involves: a) Lower cost of kilogramproduced calf from the commercial herd standpoint because to its lower commercial value when comparedto adult bull sale and longer useful lifetime. From seedstock herd view reduce time to sale by 12 months andthus lower cost too. b) Reduces generation interval gaining in genetic progress and selection pressure. c) Inheifers, genetic correlations between traits decreases pubertal age. The aim of this work was assessment ofscrotal circumference as predictor of pubertal phase start in Angus yearling bulls grown in grassland. Studieswere performed in several properties, Buenos Aires province, Argentina, involving 286 yearling bulls thatwhere born between July and September. All the bulls were raised in natural grazing conditions. Since theywere weaned every 28 days live weight and scrotal circumference were measured. When bulls reached 26cm scrotal circumference, sperm was obtained by electric stimulation of ejaculation. Sperm motility andspermatic concentration were taken from this sample. Puberty was explained when ejaculate shows spermaticconcentration of 50 x 106 sperm by milliliter and lineal motility was 10%. Scrotal circumference was evaluatedas predictor of puberty by an analysis of the ROC curve using the statistical package STATA 11. Cut offvalue of scrotal circumference obtained as puberty predictor was 28 cm. Canadian studies conducted in grainfeeding conditions stated a scrotal circumference cut off value of 30 cm. Sensitivity and specificity results forscrotal circumference regarding the arrival at puberty determined by seminal quality were 84.6% and 80.0%respectively. This means that 15.4% of yearling bulls considered pubertal were not reached this stage; and20% of individuals were misclassified as immature and they really were in their puberty. This results are inconcordance with those published for Angus bulls. Obtained values are moderate to high and indicate thattrough the scrotal circumference measurement there is a good probability of accurately classifying animals.We concluded that under Argentinian grassland conditions if we directed selection in favor of sexual precocity,and there were restrictions for conducting seminal quality assessments, the scrotal perimeter would be anoption because of its practicality, repeatability and low cost.