Comparation between performance data of yearlings and 2 years old Nellore heifers - preliminary data

Aiming to diminish the backgrounding of the heifers associated to usage of genetic selection to precocious calving (PC), yearling Nelore heifers have been breeding to become pregnant at this early age. The PC has positive correlation with economic carachteristics that impact the beef operation system. The aim of this trial was to evaluate retrospectively the productive data of heifers that became pregnant between 12 to 16 montns (Precocious = P) or 24 to 27 months (Not precocious = NP). A total of 305 heifers born between September and November of 2010 and weaned between May and July of 2011 received a 600 grams/animal/day protein mixture between May and December. At December of 2011, all heifers received an induction of puberty protocol following timed artificial insemination (TAI) according to Rodrigues et al., (Theriogenology, 82, 760, 2014). After the TAI, heifers were exposed to bulls in a proportion of one bull for 30 heifers until March 2012 (2011/2012 breeding season; BS). Heifers that become pregnant in the first BS were classified as P (n=164) and heifers that were not pregnant were classified as NP (n=141). The NP heifers went to the next BS (2012/2013) with 24 to 27 months of age. All heifers were evaluated in the subsequents BS (2012/2013 and 2013/2014). The data was retrospectively compared two groups (P vs. NP) of heifers: number of gestations, calving rate and number of weaned calves, total weight (Kg) of weaned calf, pregnancy loss, calf mortality, weight of heifer at weaning, weight of heifer at beggining of BS and mature weight. Mature weight was achieved at appoximately 44 months of age. Data were analyzed using MIXED procedure from SAS. There was no difference between age of heifers of P and NP group (432 days = 14.1 mo). The P heifers presented higher number of gestations (2.3 ± 0.05 vs. 1.2 ± 0.06), number of calvings (2.1 ± 0.06 vs. 1.2 ± 0.07) and number of weaned calves (1.4 ± 0.04 vs. 0.7 ± 0.05) compared to NP group (P < 0.05), respectively. Total weight of calf weaned (Kg) was higher to P group (312.5 ± 10) compared to NP (146.8 ± 11). Pregnancy loss (%) were higher for P (14.0) group compared to NP (4.3). There was no difference in calf mortality (10.5%), weight of heifers at weaning (214.1 ± 1.8), at beggining of BS (280.0 ± 1.7) and the mature weight (445.1 ± 3.6) of P and NP heifers. The pregnancy rates (%) at TAI and at end of BS when primiparous was 41.6a and 67.9x for P and 27.9b and 60.4y for NP, respectively. Weight of calves at weaning (Kg) for first and second parurition of P group was 211a and 233b , allthough was 206a for primiparous cows of NP group. In conclusion, yearling Nelore heifers increase the total weight of calf weaned, even with higher pregnancy loss, and also not alter their mature weight. Further prospective studies certainly should be necessary to validate these results.