Use of Nelore clarifide molecular markers for predicting reproductive rates in heifers

Studies indicate that the Molecular Value Prediction (MVP) for reproductive characteristics, such as Early Pregnancy Probability (EPP) and Age at First Calving (AFC), can be used as a tool to predict the future reproductive performance of cows (Evans et al., 1999; Doyle et al., 2000; Donoghue et al, 2004). The aim of this study was to evaluate correlations between MVP (EPP and AFC) and reproductive performance of Nellore beef heifers. A total of 908 heifers (263.0 ± 27.4 Kg, 17.6 ± 1.0 months), on Brachiaria decumbens pasture with protein supplementation (0.1% BW) were genomically evaluated (CLARIFIDE Nelore, Zoetis). All heifers were submitted to a protocol for cyclicity induction, followed by synchronization of ovulation and TAI. Heifers that did not become pregnant to TAI were resynchronized and then exposed to natural service for 90 days. Ultrasound evaluations were performed to evaluate the cyclicity induction protocol (CL presence at beginning of TAI protocol) and the pregnancy rate at the end of the breeding season. Statistical analyzes were conducted in SAS 9.3 (SAS Institute, Cary, NC, USA) using the PROC LOGISTIC to evaluate the binomial variables and the PROC GLM to evaluate continuous variables. There was an effect of EPP-MVP on the response to cyclicity induction protocol (P = 0.005), in which each percentage point increase in EPP-MVP improved by 5% the probability of cyclicity induction. Heifers with lower value for AFC-MVP tended (P = 0.1) to have better pregnancy rate at the end of the breeding season. The EPP-MVP and AFC-MVP provided by CLARIFIDE Nelore genomic tool allowed the identification of heifers with higher probability to respond to cyclicity induction protocol and that tended to have a higher probability of pregnancy at the end of breed season.