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

DE IRAOLA, J J; BONAMY, M; BALDO, A; GIOVAMBATTISTA, G; PRANDO, A J; BALBI, M

Foz do Iguaçu

Congreso; 54 Reuniao Anual da Sociedade Brasileira de Zootecnia; 2017

Sociedade Brasileira de Zootecnia

Pregnancy rates achieved by yearling bulls (15 months old of age) in natural breedingare similar to those obtained by adult breeding males. Reproductive use of yearling bullsinvolves: a) Lower cost of kilogram produced calf from the commercial herd standpointbecause to its lower commercial value when compared to adult bull sale and longer usefullifetime. From seedstock herd view reduce time to sale by 12 months and thus lower costtoo. b) Reduces generation interval gaining in genetic progress and selection pressure.c) In heifers, genetic correlations between traits decreases pubertal age. The aim of thiswork was assessment of scrotal circumference as predictor of pubertal phase start inAngus yearling bulls grown in grassland. Studies were performed in several properties,Buenos Aires province, Argentina, involving 286 yearling bulls that where born betweenJuly and September. All the bulls were raised in natural grazing conditions. Since theywere weaned every 28 days live weight and scrotal circumference were measured. Whenbulls reached 26 cm scrotal circumference, sperm was obtained by electric stimulation ofejaculation. Sperm motility and spermatic concentration were taken from this sample.Puberty was explained when ejaculate shows spermatic concentration of 50 x 106 spermby milliliter and lineal motility was 10%. Scrotal circumference was evaluated as predictorof puberty by an analysis of the ROC curve using the statistical package STATA 11. Cutoff value of scrotal circumference obtained as puberty predictor was 28 cm. Canadianstudies conducted in grain feeding conditions stated a scrotal circumference cut off valueof 30 cm. Sensitivity and specificity results for scrotal circumference regarding the arrivalat puberty determined by seminal quality were 84.6% and 80.0% respectively. Thismeans 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 in concordance with those published for Angus bulls. Obtained valuesare moderate to high and indicate that trough the scrotal circumference measurementthere is a good probability of accurately classifying animals. We concluded that underArgentinian grassland conditions if we directed selection in favor of sexual precocity, andthere were restrictions for conducting seminal quality assessments, the scrotal perimeterwould be an option because of its practicality, repeatability and low cost.