Browsing by Subject "Residual feed intake"
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Item An Exploration of Biological Mechanisms that Impact Intake and Feed Efficiency in the Grazing Animal(2013-05-21) Wiley, LeanneBiological mechanisms that potentially contribute to residual feed intake (RFI) have not been fully understood in the grazing animal. The objective of this study was to determine the differences of RFI measured in confinement (RFIc) or grazing (RFIg) on animal performance. Animals were previously classified in confinement as high RFI (HRFIc), or low RFI (LRFIc) and subsequently under grazing as high (HRFIg) or low (LRFIg). Effects of forage quantity on dry matter intake (DMI), and biological mechanisms that contribute to variations in RFI were investigated using ultrasound, carcass traits and bacterial populations. Bulls were allotted to replicate bermudagrass pastures at low (LSTK) or high (HSTK) stocking intensities and heifers grazed one Ryegrass pasture. Ruminal microbial content was collected and profiled using bacterial tag-encoded FLX amplicon pyrosequencing technique. In 2009, bulls were harvested directly off the pasture and ultrasound and carcass measurements were determined. Data were analyzed using PROC GLIMMIX of SAS. Linear regressions were obtained using PROC REG to estimate RFI. In 2009, there was a difference for LRFIc bulls in F:G (P=0.032), and HRFIg bulls on LSTK had an interaction for ADG (P=0.043). HRFIg bulls had greater intakes regardless of STK (P=0.003). In 2010, HRFIc bulls remained heavier throughout with the greatest DMI (P=0.0095). There were no differences for any traits for 2010 RFIg bulls. At a LSTK, HRFIg bulls tended (P>0.05) to have a lighter gastrointestinal tract (GIT) weight (P=0.093) while liver weight (P=0.072) tended to be heavier for all bulls. The small intestine was heavier for LRFIg bulls (P=0.09) on a HSTK. There was an interaction for microbial bacteria identified in the rumen in 2009 on hemicellulolytic (P=0.048), starch (P=0.025), and pectinolytic (P=0.057) degrading bacteria. HRFIg bulls at a LSTK had a greater percentage for amylolytic and pectinolytic degrading bacteria (P=0.008 and P=0.051, respectively) in the large intestine. There were no interactions for any substrates in 2010. DMI (P<0.0001) was greater each year for HRFIc heifers and was greater (P=0.0168, P=<0.0001, P=<0.0001) each year respectively for LRFIg heifers. No differences were found for initial BW, final BW, MetBW, and ADG in the RFIc or RFIg classes. HRFIg bulls with the greatest forage availability consumed more and had heavier GIT, but it is still unclear how the microbial fauna affected the efficiency among RFI phenotyped bulls.Item Phenotypic Characterization of Feed Efficiency and Feeding Behavior Traits in Performance Tested Bulls Fed a Corn Silage-Based Diet(2013-01-14) Moreno Rajo, Jose GilbertoObjectives of this study were to characterize feed efficiency traits and examine phenotypic relationships with feeding behavior traits in bulls. Performance, feed intake and feeding behavior traits were measured in bulls (n = 5,165) representing 2 breeds (4100 Angus and 952 Red Angus). Intake and feeding behavior traits were measured for 70-d using a GrowSafe system while fed a corn silage based diet (ME = 2.50 Mcal/kg DM). BW was measured at 14-d intervals. Residual feed intake (RFI) was calculated as the difference between actual DMI and that expected from regression of DMI on mid-test BW0.75 (MBW) and ADG, and residual gain (RG) as the difference between actual ADG and that expected from regression of ADG on MBW and DMI. Residual gain and intake (RIG) was computed as the sum of -1 x RFI and RG, both standardized to a variance of 1. Results from the study indicate that RFI was correlated with DMI (r = 0.71, P < 0.0001) but not MBW or ADG, whereas, RG was correlated with ADG (r = 0.87, P < 0.0001) but not MBW or DMI. RFI was negatively correlated with G:F (r = -0.53, P < 0.0001) and RG (r = -0.40, P < 0.0001). Feeding bout (FB) frequency and duration were correlated with RFI (r = 0.30, 0.36; P < 0.001), but were not significant or weakly correlated (r < 0.10) with RG and G:F. Meal criterion and duration were both correlated (r = -0.13, 0.22; P < 0.0001) with RFI, but not with RG or G:F. Bulls with low RFI spent less time at the feed bunk (129 vs 151 ? 31.2 min/d) and had fewer FB events (79 vs 91 ? 23.4 events/d) than high-RFI bulls. Low-RFI bulls had longer (P < 0.001) meal criterion (9.9 vs 8.5 ? 6.6 min) indicating they took longer to initiate new meals, and had longer meal durations (223 vs 244 ? 43.5 min/d) than high-RFI bulls. Bulls have distinctive feeding behavior patterns that contribute to between-animal variation in RFI, but not associated with RG or G:F.Item Sources of biological variation in residual feed intake in beef cattle(2009-05-15) Lancaster, Phillip AllanObjectives 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.