Abstract

ROMERO MONTELEONE, S.I. et al. Replacement heifers in cow-calf systems: impact of morphostructural and developmental characters on reproductive performance. Rev. vet. [online]. 2024, vol.35, n.1, pp.42-47. ISSN 1669-6840.  http://dx.doi.org/10.30972/vet.3517478.

The breeding of replacement heifers in breeding systems is an important factor that directly affects the productivity of livestock companies. The aim of this study was to assess the reproductive performance of replacement heifers during their first breeding season, considering morphostructural and reproductive development variables. 142 zebu cross females of 22 to 24 months of age were used, previously selected by weight (a minimum of 67% of the estimated weight for an adult cow under the system was considered). An observational design was used before service in which they were divided into 3 groups according to the degree of reproductive development (RTS 1 to 3), live weight (LW), body condition (BCS 1-9), and zoometric measurements. The service was carried out by artificial insemination at a fixed time (TAI) and natural service (NS). The pregnancy diagnosis was carried out 32 days after the TAI and 35 days after the bulls were removed for NS. The results showed significant differences between the growth and development variables, except in cannon bone circumference and rump height. For LW the RTS1 were 10% heavier than the RTS3. The χ2 test identified association between NS and RTS with 50, 82 and 32%, as well as in general pregnancy of 84, 92 and 67% pregnancy in RTS1, 2 and 3, respectively. In conclusion, for the pre- breeding selection of replacement heifers, it is essential to consider not only live weight but also the degree of reproductive development and zoometric variables.

Keywords : replacement heifers; first service weight; reproductive tract scoring; pregnancy.

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