Relationships between postweaning residual feed intake in heifers and forage use, body composition, feeding behavior, physical activity, and heart rate of pregnant beef females.

摘要

The objectives of this study were to determine if residual feed intake (RFI) classification of beef heifers affected efficiency of forage utilization, body composition, feeding behavior, heart rate, and physical activity of pregnant females. Residual feed intake was measured in growing Bonsmara heifers for 2 yr (n=62 and 53/yr), and heifers with the lowest (n=12/yr) and highest (n=12/yr) RFI were retained for breeding. Of the 48 heifers identified as having divergent RFI, 19 second-parity and 23 first-parity females were used in the subsequent pregnant-female trial. Pregnant females were fed a chopped hay diet (ME=2.11 Mcal kg-1 DM) in separate pens equipped with Grow Safe bunks to measure individual intake and feeding behavior. Body weights were measured at 7-d intervals and BCS and ultrasound measurements of 12th-rib fat depth, rump fat depth, and LM area obtained on d 0 and 77. Heart rate and physical activity were measured for 7 consecutive d. First-parity females had lower (P<0.05) initial BW, BW gain, and initial hip height and tended (P=0.07) to have lower DMI compared to second-parity females. Females with low RFI as heifers consumed 17 less (P<0.01) forage compared to females with high RFI as heifers but maintained the same BW, BW gain, and body composition. Likewise, RFI classification did not affect calving date. An interaction (P=0.04) between heifer RFI classification and parity was found for calf birth weight. Calves from first-parity low-RFIfemales were lighter at birth (P<0.01) than calves from high-RFI females, but RFIclassification did not affect BW of calves born to second-parity females. Residual feed intake classification did not affect bunk visit frequency, but low-RFIfemales spent 26 less time (P<0.01) at the bunk compared to high-RFIfemales. First-parity females had more (P<0.05) daily step counts and greater lying-bout frequencies compared to second-parity females, but physical activity was not affected by RFIclassification. Heart rates of females classified as low RFIwere 7 lower (P=0.03) compared to high-RFI females. Heifer postweaning RFIbut not G:F or residual gain were positively correlated with forage intake (r=0.38) and RFI (r=0.42) of pregnant females. Results indicate that heifers identified as having low postweaning RFI have greater efficiency of forage utilization as pregnant females, with minimal impacts on growth, body composition, calving date, and calf birth BW, compared to their high-RFI counterparts.Digital Object Identifier http://dx.doi.org/10.2527/jas.2013-6423