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Use of residual feed intake as a selection criterion on the performance and relative development costs of replacement beef heifers

Damiran, D., Penner, G.B., Larson, K., Lardner, H.A. (Bart)
The Professional animal scientists 2018 v.34 no.2 pp. 156-166
Angus, beef cattle, calving, diet, feed conversion, feed intake, feed prices, heifers, pregnancy rate, reproductive efficiency, reproductive performance, weaning
Two heifers groups differing in residual feed intake (RFI) were compared with a third control (CON; n = 20) group of randomly selected heifers for performance, reproductive efficiency, and system economics to first calving and repeatability of RFI ranking, with all 3 groups selected from the same cohort. Following weaning, 70 Angus heifers (initial BW = 260 ± 3 kg; 6 mo of age) from a single cohort were fed a forage-based diet (10.0% CP; 65.2% TDN) for 93 d (period 1) where BW, DMI, ADG, G:F, and RFI were evaluated. After period 1 RFI testing, 40 heifers were classified into 2 groups [20 efficient heifers (low RFI; RFI = −1.01±0.10 kg/d) and 20 inefficient heifers (high RFI; RFI = 0.77±0.08 kg/d)] and then selected for a second feeding trial (period 2) and compared with the 20 CON heifers. All 60 heifers in period 2 (BW = 322 ± 2.9 kg; 10 mo of age) were fed for 93 d on a similar forage-based diet (11.0% CP; 66.5% TDN). Low-RFI heifers had the lowest (P = 0.01) RFI value of −0.33 kg/d, followed by CON and high-RFI heifers, −0.09 and 0.42 kg/d, respectively. Control heifers tended (P = 0.08) to have lower ADG (0.83 kg/d) compared with low-RFI (0.92 kg/d) or high-RFI heifers (0.91 kg/d), and low-RFI heifers tended (P = 0.08) to have greater G:F (0.10 ± 0.003) than either CON (0.9 ± 0.003) or high-RFI heifers (0.09 ± 0.003). Spearman rank correlation for RFI between period 1 and 2 was 0.58 (P < 0.01); however, 51% of heifers had a different RFI value in period 2 compared with period 1. First-calf pregnancy rates were 80% for low RFI, 93% for CON, and 100% for high RFI (χ2; P = 0.09). Winter feed costs were ~Can$25 per heifer lower for low-RFI heifers compared with high-RFI animals. Heifers with increased feed efficiency may exhibit reduced reproductive performance, suggesting further research is needed.