摘要
Abstract (Summary)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 12 th 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.
摘要译文
这项研究的摘要（摘要）目的是在不断增长的牛犊来表征剩余采食量（RFI），并检查与生长，胴体组成，生理指标，能量代谢和繁殖的关系。为了实现这些目标，多个实验。在所有实验中，RFI计算为实际的DMI之间的差异，并预期DMI从DMI对中期试验代谢BW和日增重线性回归。审查RFI和速率和生长的组合物，和重放之间的实验用断奶后Brangus母牛（N = 348）进行的关系。胎体组合物（最长肌区，LMA;和12个肋脂肪厚度，BF）的措施，通过超声在各实验的开始和结束时，获得。以确定是否血清IGF-I浓度与RFI相关联，两个实验进行了与安格斯牛和小母牛（N = 95）发散地选择用于血清IGF-I浓度。为了评估与能量代谢的关系，牛犊，低和高的RFI被选择用于确定心脏速率的作为指示剂的特质对能量消耗（4个实验）和肝线粒体功能（3个重复）.Residual采食量未与ADG相关，但增益高炉，这样更有效的犊牛精简呈正相关。从低IGF-I的选择线牛犊有较低的RFI表明RFI和IGF-I是相关的，即IGF-I的可作为一个指标性状的选择，以帮助在安格斯牛改进的RFI。犊牛低RFI有较低的能量消耗，比小牛高RFI提示能量代谢的调节改善线粒体更大的控制受体比例。小母牛具有低的RFI的类似百分比达到青春期那些具有高的RFI由实验结束。这项研究的结果表明，生产商可以利用RFI选择与生长，胴体组成和繁殖的影响最小提高饲料效率。
Lancaster, Phillip Allan. Biological sources of variation in residual feed intake in beef cattle[D]. US: Texas A&M University, 2008