We aimed to evaluate the effects of early weaning on the productive and reproductive characteristics of Nelore heifer progeny. Ninety-five calves from primiparous (PRI) and multiparous (MUL) dams were assigned to one of two weaning strategies; 1) early weaning at 150 d (149 ± 1.97) of age (EW; n = 16 from PRI and 31 from MUL); or 2) conventional weaning at 240 d (247 ± 2.41) of age (CW; 16 from PRI and 32 from MUL). All heifers received ~5 g/kg of body weight (BW) of creep-feed as fed from 90 d of age until weaning. After weaning, each group of heifers was transferred to a Brachiaria spp. paddock and received 5 g/kg of BW of a protein-energy supplement until 12 mo of age. Then, heifers were confined and fed a diet with a ratio of 79:31 (corn silage: concentrate) for 4 mo, during which they were submitted to a hormonal protocol to induce puberty and timed artificial insemination (TAI). Reproductive tract score (RTS, 1 to 5 scale: 1 being infantile and 5 being cyclic) and endometrial thickness were determined at 12 mo of age, rump fat thickness (RFT), and BW every 28 ± 4 d through the breeding season, and plasma concentrations of IGF-I were evaluated at 12, 14, and 16 mo. At 15.6 mo of age heifers were submitted to a P4/E2 protocol for TAI at day 0 (D0), and a second TAI was performed at D22 in nonpregnant heifers. Ultrasound was used to determine the presence of corpus luteum on D10 and dominant follicle (DF) diameter and blood perfusion on D2 and D0. Data were analyzed using SAS by ANOVA or logistic regression. Though heifers from EW were lighter (P < 0.05) than CW at postweaning time points and CW presented a greater (P = 0.002) RFT than EW heifers from 11 to 15 mo, weaning strategy did not affect (P > 0.1) body condition score at TAI. Concentrations of IGF-I did not differ (P > 0.1) between heifers weaned at 150 and 240 d. The proportion of pubertal heifers, endometrium tone and thickness, and RTS at 16 mo did not differ (P > 0.1) between EW and CW groups. The diameter of DF on D2 and D0 and follicular blood perfusion on D0 were greater (P < 0.05) for heifers in the CW group than EW group, but P/AI at first and second TAI did not differ (P > 0.1) between groups. In conclusion, early weaning in Nelore heifers moderately reduces postweaning growth but does not affect puberty and reproductive performance before the breeding season when submitted to confinement.
Keywords: Beef cattle; IGF-I; TAI; puberty; reproductive tract score.
In beef cattle operations, heifers represent the most current genetic improvement and are integral to the future of the herd. Factors such as age and weight at weaning and average daily gains impact fertility and longevity of beef heifers. The present study compared the effects of two weaning strategies (150 d of age vs. 240 d of age) on the growth and reproductive characteristics of Nelore Heifers. Comparing the weaning strategies of Nelore heifers, the present study indicates that: 1) heifers weaned at 150 d were lighter than heifers weaned at 240 d; and 2) puberty, concentration of IGF-I, and reproductive tract development and performance did not differ between weaning strategies. Shows that early weaning in Nelore heifers moderately reduces postweaning growth but does not affect reproductive performance.
© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.