Browsing by Subject "Residual Feed Intake"
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Item Determining biological sources of variation in residual feed intake in Brahman heifers during confinement feeding and on pasture(2009-05-15) Dittmar (III), Robert OttoObjectives were to characterize residual feed intake (RFI) and determine the phenotypic correlation between performance, feed efficiency, and other biological measurements in Brahman heifers, as well as the relationship between RFI determined in confinement and measurements of grazing activity on pasture. Three separate 70 d feeding trials were performed, and RFI was determined as the residual between actual and predicted dry matter intake (DMI) for a given level of production. Brahman heifers (n = 103; 5-to-9 mo of age) were individually limit-fed a pelleted 12% CP complete ration daily in Calan gates. Weekly body weight (BW) and DMI data were collected, and predicted DMI was determined by linear regression of actual DMI on mid-test metabolic BW. Ytterbium chloride was used to evaluate digestive kinetics, and fecal samples were collected to determine fecal volatile fatty acids (VFA) concentration and determine apparent dry matter digestibility (DMD) utilizing acid insoluble ash as an internal marker. Measurements of temperament were evaluated on all heifers at weaning. High (n = 6) and low (n = 6) RFI heifers (Exp. I) grazed fescue and ryegrass to determine variation in grazing behavior, DMI, and apparent DMD. Data from all three experiments were pooled, and RFI was not correlated with average daily gain (ADG), DMI, BW, partial efficiency of gain, feed conversion ration, fecal VFA concentration, or any measures of temperament. There were no significant differences in digestive kinetics between the RFI efficiency groups. Fecal samples taken for acid detergent insoluble ash (ADIA) determination were not collected at frequent enough intervals to account for weekly variation in fecal ADIA concentration. Pasture measurements were not different between the efficiency groups for heifers evaluated for grazing behavior, as well as estimated intake as a proportion of BW, or apparent DMD. Results of this study suggest that Bos indicus cattle appear to have similar efficiency traits as Bos taurus and Bos indicus influenced cattle, making this measure of efficiency equally as valid for use in both types of cattle. This indicates that selection based on RFI can be made to increase feed efficiency without affecting ADG or BW in Brahman cattle.Item Effects of Residual Feed Intake Classification on Feed Efficiency, Feeding Behavior, Carcass Traits, and Net Revenue in Angus-Based Composite Steers(2012-02-14) Walter, JoelThe objectives of this study were to evaluate the effects of residual feed intake (RFI) classification on performance, feed efficiency, feeding behavior and carcass traits, and to determine the relative importance of individual performance and carcass measurements on between-animal variation in net revenue of feedlot steers. Performance, feed intake and feeding behavior traits were measured in 508 Angus-based composite steers, using the GrowSafe feed-intake measurement system, while fed a high-grain diet for 70 days. Residual feed intake (RFI) was computed as actual minus expected dry matter intake (DMI) derived from regression of DMI on average daily gain (ADG) and mid-test BW0.75, and steers classified into low (n = 150), medium (n = 200) and high (n = 158) RFI groups. Following the feed-intake measurement periods, steers were fed the same diet in group pens and harvested at an average backfat thickness of 1.14 cm. Net revenue (NR) was calculated as carcass value minus feeder calf, yardage, and feed costs using 3-year average prices. Feed cost was based on actual feed consumed during the feed-intake measurement periods, and model-predicted intake adjusted for RFI during the group-feeding periods. Steers with low RFI had $48/hd lower (P < 0.0001) feed cost, $16/hd numerically higher (P = 0.29) carcass value, and $62/hd more favorable (P < 0.0001) net revenue compared to their high-RFI counterparts. Net revenue was correlated with carcass weight, marbling score, yield grade, DMI, ADG, RFI and G:F ratio where animals that consumed more feed, had higher rates of gain and were more efficient had more favorable net returns. Models predicting net revenue from performance, carcass quality, and feed efficiency traits accounted for 77% of the between-animal variation in NR. In the base model, that included all traits performance, carcass quality and feed efficiency traits explained 28, 14 and 35%, respectively, of the variation in NR. Results from this study indicate that between-animal variation in net revenue was impacted to a great extent by performance and feed efficiency, rather than carcass quality traits, in Angus-based composite steers based on average 3-year pricing scenarios.Item Energy Expenditure in Growing Heifers with Divergent Residual Feed Intake Phenotypes. Effects and Interaction of Metaphylactic Treatment and Temperament on Receiving Steers(2011-10-21) Paddock, Zachary DeanCattle classified as having low residual feed intake (RFI) phenotypes are those that consume less feed than expected based on body weight and growth performance. Mechanisms contributing to the variation in RFI are not fully understood. Previous studies have shown that cattle of divergent RFI phenotypes have different levels of energy expenditures, which are associated with heat increment, basal metabolism, thermoregulation responses, and physical activity. The objectives of this experiment were to characterize residual feed intake (RFI) in growing heifers and to determine if variation in whole-animal energy expenditure contributes to differences in RFI. Brangus heifers (n =120) were individually fed a roughage-based diet (1.93 Mcal ME/kg DM) diet twice daily and feed refusals measured weekly. Heifers were weighed once weekly for 70 d and RFI calculated as the difference between actual and expected DMI from linear regression of DMI on ADG and mid-test BW0.75. Immediately following the 70 d study, oxygen pulse rate (mL O2/heart beat) and 48-h heart rates were measured on 8 high and 8 low RFI heifers to estimate energy expenditure. Daily heart rates and oxygen pulse rates were higher (P < 0.05) in heifers with high RFI compared to those with low RFI. As a result, energy expenditure (kcal/BW0.75) was estimated to be 17.4 percent greater (P < 0.05) in high-RFI heifers then low-RFI heifers. Mortality and morbidity losses caused by bovine respiratory disease (BRD) continue to negatively impact the net revenues of the beef cattle industry. Stress can predispose calves arriving at feedlots to BRD by impairing their immune system with calves having more excitable temperaments possibly having a greater risk. The objectives of the second study was to examine the effects of metaphylactic treatment and temperament on performance, feed intake, feed efficiency, and feeding behavior traits in steers. Santa Gertrudis steers (n =119) were weighed and randomly to control (CON; no antimicrobial treatment) or metaphylactic (MET; 1.5 mL/45 kg BW of ceftiofur crystalline free acid) treatments. Steers were weighed at 14-d intervals and individual intakes and feeding behavior traits measured using a GrowSafe sytems while fed a roughage-based diet (2.21 Mcal ME/kg DM). Objective (relative exit velocity; REV) and subjective (chute score; CS) measurements of temperament were measured on arrival and on day 28 of the study. Steers with higher REV weighed less, grew slower, consumed less feed, spent less time consuming feeding, had more feeding bouts per meal, had less backfat, smaller longissimus muscle area, and higher cortisol levels. Steers treated with MET had higher ADG than those receiving CON. Cattle with higher REV that received MET had less of a decrease in ADG, DMI, time spend consuming feed, and less of an increase in feeding bouts compared to high REV steers receiving CON. Results from this study suggest that process-control strategies, which quantify and manage inter-animal variation in calf temperament may facilitate more judicious use of antimicrobial products and provide more consistent and predictable responses to metaphylactic strategies.Item Examining Mechanisms Contributing to the Biological Variation of Residual Feed Intake in Growing Heifers and Bulls and in Mid-Gestation Females(2012-10-19) Hafla, AimeeThe objectives of this study were to characterize residual feed intake (RFI) in growing bulls and heifers and in mid-gestation females to examine relationships with performance, body composition, feeding behavior, digestibility (DMD) and heart rate (HR) and evaluate the impact of RFI on bull fertility and cow forage utilization. Additionally, use of the n-alkane method to predict individual animal variations in intake was investigated. To accomplish these objectives, multiple RFI studies were conducted. In all studies RFI was computed as the difference between actual and expected DMI from linear regression of DMI on mid-test metabolic BW and ADG. To evaluate phenotypic relationships between feed efficiency, scrotal circumference (SC) and semen-quality an experiment was conducted with yearling bulls (N=204). Residual feed intake was not correlated with BW and ADG, but was positively associated with 12th-rib back fat (BF) such that the more efficient bulls were leaner. Bulls with low RFI had similar SC and progressive motility of sperm compared to high-RFI bulls. However percent normal sperm were weakly associated with RFI in a negative manner. To examine phenotypic relationships between heifer postweaning RFI, and performance, efficiency, HR, and DMD of mid-gestation cows, RFI was measured in growing Bonsmara heifers (N=175). Forty-eight heifers with divergent RFI were retained for breeding. Subsequently, intake, performance and feeding behavior was measured on mid-gestation females. Pregnant females classified as having low postweaning RFI continued to consume 22% less feed, spent 25% less time eating, and had 7% lower HR while maintaining similar BW, ADG and body composition compared to high RFI females. A moderate association between RFI in growing heifers and subsequent efficiency of forage utilization in pregnant cows was found. Growing heifers identified as efficient had greater DMD, however DMD in mature cows was similar between RFI groups. The n-alkane method of predicting intake detected differences in intake between divergent RFI groups in mid-gestation females. Results from this study indicate that inclusion of RFI as a component of a multi-trait selection program will improve feed efficiency of growing animals and mid-gestation females with minimal impacts on growth, body composition, and fertility traits.