Heterosis Effects on Reproductive Traits in a Multibreed Beef Cattle Herd in Panama

Abstract The aim of this study was to estimate the influence of heterosis and breed percentage on calving interval (CI) and gestation length (GL), and the correlation between age at first calving (AFC) and CI, in beef cows. Data included 1,291 repeated observations of CI and GL from 502 cows with 2,840 individuals in the pedigree, including 3 generations from the multi-breed herd of the livestock experimental station of the Panama Agricultural Innovation Institute (IDIAP) in Gualaca, Panama. The herd was composed of the following genetic groups based on their breed percentage: tropically adapted Brahman (BR), Nellore (Ne), Undefined Bos indicus (BI), Guaymi Creole (CR), Senepol (SP) and Romosinuano (RS); Bos taurus (BT), Simmental (SM), Angus (A), Red Angus (AR), Limousin (LM), Charolais (CH), Wagyu (Wa), and Others (Oth); crossbreeds (cx), Beefmaster (BF), Three CX (F1 x different BT), R1(Backcross BR), R2 (Backcross BT), Composite (combination of at least 4 different breeds with less than 25% of Zebu), Upgrade (87.5% BR 12.5% BT), B1 (62.5% Zebu + 37.5% BT), and B2 (62.5% BT + 37.5% Zebu). The Zebu influenced breed group represents 50.03% of this population, followed by the F1, the three CX, composites, and R1, representing 22%, 13.89%, 6.11%, and 5.34%, respectively. The other breed groups represented less than 2.5% of the population. A repeated records animal model was used to estimate variance components for both CI and GL. A bivariate animal model was used to estimate the genetic correlation between CI and age at first calving (AFC). Fixed effects for all models consisted of contemporary group, age of dam, calf sex, degree of outcross, and breed percentage. Contemporary group was defined by calving year and season of birth. The average CI was 572.6 ± 140 d, with a range of 315 d to 910 d; and the average GL was 284.2 ± 6.3 d. The estimated regression coefficient for CI on heterosis was -0.114 ± 0.10 d/heterosis % (P = 0.266), and for GL was -0.01 ± 0.052 d/heterosis %. A shorter CI was observed for the F1, and three CX, with 558.7 days and 567.2 days, representing a 2.3% and 1.3% reduction in CI, respectively, when compared with the Zebu group. A larger CI was observed for the Nellore and Romosinuano breeds % with 0.17 ± 1.23 d, (P = 0.373) and 0.64± 0.13 d (P = 0.406), respectively. A low heritability (0.037 ± 0.026) for CI was estimated, with a positive genetic trend over the duration of the study. The analysis between CI and AFC revealed a moderate genetic correlation (0.49 ± 0.36) that allows the establishment of a selection program to improve AFC and CI, which would improve the fertility of this multi-breed herd in Panama.