Effects of residual feed intake and dam body weight on replacement heifer intake, efficiency, performance, and metabolic response.

Abstract

Thirty-eight Angus-based, crossbred, nulliparous beef heifers (BW = 280 ± 26.3 kg) sired by 2 Angus sires were used to determine if dam BW affected heifer performance, DMI, residual feed intake (RFI), and endocrine markers. Heifers were housed in individual pens (2.2 by 9.1 m) equipped with 2.2 m of bunk space and fed a diet (90.4% DM, 13.7% CP, 67.2% NDF, and 56.2% TDN) consisting of 87.2% bermudagrass hay and 12.8% liquid protein supplement for a 14-d adaption period and a 70-d feeding period. Individual daily feed intake was used to calculate RFI for each heifer, and heifer was the experimental unit. Two-day beginning and end BW were recorded and hip height was used to calculate frame score (FS). Heifer dams were assigned to a light (LIT; 544 ± 21.3 kg) or heavy (HEV; 621 ± 34.8 kg) BW group on the basis of mean BW at the beginning of their lactation period the previous year to determine differences in heifer offspring DMI and RFI. Based on heifer RFI ranking, heifers were classified as positive (POS; 0.34) or negative (NEG; –0.31) RFI and low (LOW; –0.45), medium (MED; 0.00), or high (HI; 0.49) RFI for analysis of BW, FS, BW gain, and DMI. There were no dam BW group × sire interactions (P > 0.10) for all independent variables. Beginning and end BW was greater (P < 0.05) for heifers out of HEV compared with LIT BW dams. Body weight gain, ADG, FS, DMI, and RFI were not significant (P > 0.10) for heifers out of HEV compared with LIT BW dams; however, a sire effect existed (P < 0.01) for BW gain, ADG, FS, and DMI. Among RFI classifications, beginning and end BW, BW gain, ADG, and FS were not different (P > 0.10) whereas DMI was greater (P = 0.03) among heifers in the POS compared with the NEG RFI group and greater (P = 0.01) among heifers in the MED and HI compared with LOW RFI group, respectively. Plasma insulin levels were greater (P = 0.03) in the NEG compared with the POS RFI heifers, and thyroxine (T4) levels were greater (P = 0.02) in the POS compared with the NEG RFI heifers. A positive relationship existed (P ≤ 0.05) between dam BW and heifer DMI (r = 0.42), beginning and end BW (r = 0.45 and 54), and FS (r = 0.58) and between RFI and d 70 triiodothyronine (r = 0.34), d 70 T4 (r = 0.35), and d 0 and 70 combined T4 (r = 0.32), respectively. Heifers out of dams from the HEV BW group were heavier and a positive correlation existed between dam BW and heifer BW, gain, DMI, and FS, which can impact selection goals for replacement heifers.