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Impact of the Sires on Puberty Onset in Nellore Heifers
In Brazil the main breed of beef cattle is Nellore, where it represents 70% of the national herd. Since the late onset of puberty one of the principal problems associated with this breed. The aim of this study was to evaluate the Expected Progeny Differences (EPDs for scrotal circumference) of sires and its effect on puberty in Nellore heifers. The daughters of 12 sires (143 calf heifers) were used. After weaning at 210 days of age, the animals were mantained in cultivated pasture of Brachiaria ssp. with mineral supplement and water ad libitum. The heifers were weighed, and the puberty onset was assessed monthly from 12 to 30 months (by ultrasonography - corpus luteum detection). The sires were classified in precocious and non-precocious groups according to the positive (PEPD, n=8) or negative (NEPD, n=4) EPD to scrotal circumference. Continuous variables were analyzed by MIXED procedure, and variables with binomial distribution were analyzed by GLIMMIX procedure, both through SAS 9.3. Heifers that were NEPD daughters had the puberty onset heavier (P=0.009) and older (P=0.013) than the PEPD daughters (weight – 317.0 ± 10.6 vs 294.8 ± 8.7 Kg; age – 644.7 ± 59.3 vs 593.5 ± 62.7 days; for NEPD and PEPD, respectively). The percentage of pubertal heifers at 14, 18, 26 and 30 months of age, not were different between NEPD and PEPD (14 months of age – 11.1 vs 8.2 %; 18 months of age - 26.7 vs 30.6 %; 26 months of age – 66.7 vs 73.5 %; 30 months of age – 93.3 vs 92.8 %, for NEPD and PEPD, respectively). We can conclude that there is genetic heterogeneity to onset puberty in Nellore breed. Furthermore, the results reveal the importance of the use of proven sires for sexual precocity. Financial support: FAPESP.
Keywords: Sexual precocity, Nellore, Sire.