| dc.description.abstract | The objectives of this study were to evaluate feed efficiency indexes (residual feed intake (RFI) and the residual body weight gain(RG)in dairy heifers and its effects on feed intake, performance, body measurements and surface body temperature. Holstein × Gyr heifers (½ Holstein × ½ Gyr; n = 36) with initial age of 146.7 ± 28.2 days (mean ± SD), initial body weight of 152.3 ± 21.7 kg, wereclassified into two groups: high efficiency (HE; RFI, n = 12; and RG, n = 12), and low efficiency (LE; RFI, n = 12; and RG, n = 12).Animals were distributed in 4 pens equipped with electronic feed and water bins and received a total mixed ratio (TMR; 75:25, corn silage: concentrate, 177.8 CP/kg and 430.6 g/kg NDFap on a dry matter basis) ad libitum.Dry matter intake, water intake and feeding behavior were measured daily, whereas the body weight was determined weekly, body measurements were taken every 15 d and maximum body surfacetemperatures were measured at 12 animalpositionssites on day 68 of the trial. The feed efficiency trial last for 113 days. RFI averagefrom LE group was 0.30 kg/d, whereas HE RFI average was -0.27 kg/d. The HE-RFI group consumed 10.39% less (0.53 kg DM/d) than LE-RFI, with no differences in ADGand body measures between both groups. For feeding behavior traits, HE-RFI group had lower feeding rate per bout and per meal compared to LE-RFI, and there were no differences in water intake between both groups. HE-RFI group had higher maximum surface temperature of the upper part of muzzle and in the right rib region compared to LE-RFI, and the difference in maximum temperature between the left and right flanks was higher and negative. The RG average of LE group was -0.09 kg/d whereas HE group had an RG average of 0.09 kg/d. The HE-RG group had an ADG of 0.95 kg/day, while the LE-RG had an ADG of 0.76 kg/day. HE-RG groupwere 2.15, 4.16, 2.72 and 2.75 cm greater compared to LE-RG group for withers height, heart girth, body depth and hip height, respectively. For feeding behavior traits, HE-RG group had higher meal frequency and average meal duration compared to LE-RG. There was no difference between RG groups for maximum body surface temperature at the evaluated animal sites. The divergence in RFI did not affected the growth rate and skeletal structure of Gyrolando F1 heifers. For RG, HE group had higher growth rate and weight gain. | |
