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

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.

Impact of cow size on dry matter intake, residual feed intake, metabolic response, and cow performance.

Thirty-eight Angus-cross beef cows were used to evaluate differences in DMI, residual feed intake (RFI), and endocrine markers on the basis of cow size and RFI ranking during 2 stages of production. Cows housed in individual pens (2.2 × 9.1 m) were fed, over a 70-d feeding period, 30% Bermuda grass hay and 70% ryegrass baleage diet during lactation (LACT) and a 100% ryegrass hay diet during postweaning (NOLACT). Individual daily feed intake, BW, and BCS were recorded, and hip height was used to determine frame score (FS). Feed intake was used to calculate RFI for each cow, and cow was the experimental unit. Blood samples were obtained on d 0 and 70 and were analyzed for glucose, insulin, leptin, triiodothyronine (T3), and thyroxine (T4). Cows were assigned to a light (LIT) or heavy (HEV) BW groups on the basis of mean BW at the beginning of the LACT period. On the basis of RFI values for each feeding period, cows were placed into a negative (NEG; RFI < 0.00) or positive (POS; RFI > 0.00) RFI group and into a low (LOW; ≤0.2 SD mean RFI), medium (MED; within ±0.19 SD), or high (HI; ≥0.2 SD mean RFI) RFI group. During LACT, DMI was 4.8% greater (P = 0.03) and FS was greater (P < 0.01; 6.4 and 5.5 ± 0.16) for the HEV compared with LIT BW cows. No RFI by day interaction or RFI group main effect occurred for endocrine markers during LACT; however, a negative relationship (P = 0.04) existed between BW group and combined T3 data, and a positive relationship (P = 0.04) existed between RFI and combined insulin data. For both LACT and NOLACT, RFI was similar (P > 0.05) among BW groups; however, DMI was 6.5% and 8.9% greater (P < 0.01) for POS compared with NEG RFI in the LACT and NOLACT periods. In LACT, DMI was greater (P < 0.01) for HI and MED RFI compared with LOW RFI, and in NOLACT, DMI was greater (P < 0.01) for the HI compared with MED and LOW RFI cows and MED compared with LOW RFI cows. During NOLACT, DMI was 8.9% greater (P < 0.01) for the HEV (12.4 ± 0.22 kg) compared with LIT (11.3 ± 0.19 kg) BW cows. Change in BCS was greater (P ≤ 0.03) in higher RFI cows in both RFI groups only in the NOLACT period. Differences in T3 and T4 on d 0 and 70 were 25% and 15% greater (P ≤ 0.04) for the LIT BW group compared with the HEV BW group. A negative correlation existed (P ≤ 0.04) between BW group and T3 and T4, as well as leptin and RFI (P = 0.03). Although cow BW was independent of RFI and T3 and T4 levels tended to be greater in lighter BW cows, DMI was consistently greater for cows with heavier BW and higher RFIvalues.