Resumen
- The objective of this research was to compare the combining ability of sires from 2 tropically adapted Bos Taurus breeds (Blanco Orejinegro: BON; Romosinuano: RS), 3 tropically adapted Bos indicus breeds (Gray Brahman: GB; Guzerat: GZ; Red Brahman: RB), and 4 temperate Bos taurus breeds (Braunvieh: BV; Limousin: LIM; Normand: NM; Simmental: SIM) when mated to Gray Brahman cows for birth weight (BW), and adjusted weights (W), ultrasound rib eye area (REA) and backfat (BF) measured at 4 (W4, REA4, BF4), 7 (W7, REA7, BF7), 12 (W12, REA12, BF12), and 15 (W15, REA15, BF15) mo of age. Data were from 352 calves (22 to 100 per breed group) sired by 37 bulls (3 to 12 sires per breed). The GB cows were from 2 herds located in an area of Colombia classified as dry tropical forest. Cows and calves were kept under pasture conditions with a complete mineral supplement. The model included breed group of calf, contemporary group (herd-year-season-sex) and age of calf (ultrasound traits only) as fixed effects and sire and residual as random effects. Least squares means (LSM) for BW, W4 and W7 were similar across breed groups, whereas calves from SIM sires were heavier than calves from GB sires at 12 (P < 0.0009)and 15 mo of age(P < 0.0008). The LSM for REA were similar for calves from all breed groups, except for crossbred calves from LIM sires whose REA were larger than those from calves from GZ (P < 0.0078), NM (P < 0.0103), SIM (P < 0.0143), and RB sires (P < 0.0002)at 4 mo age, and from GB-sired calves at all ages (P < 0.0224 to P < 0.0002). The LSM for BF were similar across breed groups and calf ages. Thus, SIM sires had the best combining ability for growth and LIM sires had the best combining ability for REA under the pasture conditions of this dry tropical forest region of Colombia.