Lancaster, Phillip Allan (2008-05). Sources of biological variation in residual feed intake in beef cattle. Doctoral Dissertation. Thesis uri icon

abstract

  • Objectives of this study were to characterize residual feed intake (RFI) in growing calves and to examine relationships with growth, carcass composition, physiological indicators, energy metabolism and reproduction. To accomplish these objectives, multiple experiments were conducted. In all experiments, RFI was calculated as the difference between actual DMI and expected DMI from linear regression of DMI on mid-test metabolic BW and ADG. To examine the relationships between RFI and rate and composition of growth, and reproduction an experiment was conducted with postweaning Brangus heifers (N = 348). Measures of carcass composition (longissimus muscle area, LMA; and 12th rib fat thickness, BF) were obtained by ultrasound at the start and end of each experiment. To determine if serum IGF-I concentration is associated with RFI, two experiments were conducted with Angus bulls and heifers (N = 95) divergently selected for serum IGF-I concentration. To evaluate relationships with energy metabolism, calves with low and high RFI were selected for determination of heart rate as an indicator trait for energy expenditure (4 experiments) and liver mitochondrial function (3 experiments). Residual feed intake was not correlated with ADG, but was positively correlated with gain in BF such that the more efficient calves were leaner. Calves from the low IGF-I selection line had lower RFI suggesting that RFI and IGF-I are related and that IGF-I could be used as an indicator trait to aid in selection for improved RFI in Angus cattle. Calves with low RFI had lower energy expenditure and greater mitochondrial acceptor control ratios than calves with high RFI suggesting improved regulation of energy metabolism. A similar percentage of heifers with low RFI attained puberty as those with high RFI by the end of the experiment. Results from this study indicate that producers can utilize RFI to select for improved feed efficiency with minimal impact on growth, carcass composition and reproduction.
  • Objectives of this study were to characterize residual feed intake (RFI) in
    growing calves and to examine relationships with growth, carcass composition,
    physiological indicators, energy metabolism and reproduction. To accomplish these
    objectives, multiple experiments were conducted. In all experiments, RFI was calculated
    as the difference between actual DMI and expected DMI from linear regression of DMI
    on mid-test metabolic BW and ADG. To examine the relationships between RFI and rate
    and composition of growth, and reproduction an experiment was conducted with
    postweaning Brangus heifers (N = 348). Measures of carcass composition (longissimus
    muscle area, LMA; and 12th rib fat thickness, BF) were obtained by ultrasound at the
    start and end of each experiment. To determine if serum IGF-I concentration is
    associated with RFI, two experiments were conducted with Angus bulls and heifers (N =
    95) divergently selected for serum IGF-I concentration. To evaluate relationships with
    energy metabolism, calves with low and high RFI were selected for determination of
    heart rate as an indicator trait for energy expenditure (4 experiments) and liver
    mitochondrial function (3 experiments). Residual feed intake was not correlated with ADG, but was positively correlated
    with gain in BF such that the more efficient calves were leaner. Calves from the low
    IGF-I selection line had lower RFI suggesting that RFI and IGF-I are related and that
    IGF-I could be used as an indicator trait to aid in selection for improved RFI in Angus
    cattle. Calves with low RFI had lower energy expenditure and greater mitochondrial
    acceptor control ratios than calves with high RFI suggesting improved regulation of
    energy metabolism. A similar percentage of heifers with low RFI attained puberty as
    those with high RFI by the end of the experiment. Results from this study indicate that
    producers can utilize RFI to select for improved feed efficiency with minimal impact on
    growth, carcass composition and reproduction.

publication date

  • May 2008