Is it possible to select body weight without compromising carcass traits and reproductive efficiency in Caracu...

The Caracu is a taurine breed adapted to Brazil's climatic conditions and has been selected for 40 + years for Body Weight (BW), maintaining performance records across multiple generations in its database. However, selecting young animals for BW can result in excessive growth, potentially impacting carcass and reproductive traits. This study aimed to estimate genetic correlations and, based on these estimates, evaluate how selection for BW (adjusted to 378 and 550 days of age for males and females, respectively) has influenced carcass traits and reproductive efficiency in this breed. The dataset contained records for BW (kg), Ribeye area (REA, cm²), Height-to-width ratio of the Longissimus dorsi muscle (HWR), Backfat thickness (BFT, mm), Rump fat thickness (RFT, mm), Yearly scrotal circumference (SC, cm), and Days to calving (DC, days) from animals born between 1966 and 2022. (Co)variance components were estimated by Bayesian inference using two-trait animal models. Analyses were conducted to estimate genetic parameters for pairs of traits, including BW with carcass traits (BW × REA, BW × HWR, BW × BFT, and BW × RFT) and BW with reproductive traits (BW × DC and BW × SC). Additionally, analyses were performed for pairwise combinations among carcass traits (REA × HWR, REA × BFT, REA × RFT, HWR × BFT, HWR × RFT, and RFT × BFT) and between reproductive traits (DC × SC). The relationship matrix included 4,783 animals, of which 829 were genotyped with the GGP Bovine 100 K SNP panel. Favorable genetic correlations (r_g) were observed between BW and REA (0.51 ± 0.11), HWR (0.45 ± 0.17), SC (0.24 ± 0.13), and RFT (0.15 ± 0.21), with the latter being favorable but low. On the other hand, unfavorable genetic correlations were observed between BW and BFT (-0.07 ± 0.21), which was unfavorable but close to zero relationship, and between BW and DC (0.48 ± 0.15). The significance of carcass and reproductive traits is underscored by the favorable, r_g between BW and the carcass traits REA (BW × REA) and HWR (BW × HWR), while a high, unfavorable r_g was observed between BW and DC cows. These findings emphasize the importance of carefully balancing genetic selection to optimize growth, carcass quality, and adequate reproduction in Caracu cattle.