Objectives of this study were to determine if variation in energy expenditures contributed to differences in feed efficiency between low and high RFI steers. Nine steers with the lowest and highest residual feed intakes (RFI) were selected from 169 Braunvieh-sired crossbred steers that were individually fed a pelleted roughage-based diet for 77 d. Following the RFI measurement period, heat production (HP) measurements were obtained using indirect calorimetry while steers were fed the same roughage diet (RD) and on a high-concentrate diet (CD). Linear regression analyses of log HP or retained energy on ME intake were used to determine energy partitioning. Motion and lying activity were measured concurrently with HP on the RD and CD. During the RFI measurement period, low RFI steers had lower (P < 0.01) RFI (-1.7 vs. 1.6 ± 0.17 kg/d), DMI (7.7 vs. 10.2 ± 0.42 kg/d) and feed:gain ratio (F:G; 7.2 vs. 10.6 ± 0.60), but similar final BW and ADG compared to high RFI steers. However, there were smaller differences in DMI (8.4 vs. 9.7 ± 0.38 kg/d; P < 0.05; 7.56 vs. 8.16 ± 0.31; P = 0.19) and F:G (10.0 vs. 10.9 ± 0.40; P = 0.36; 6.5 vs. 7.5 ± 0.30; P < 0.05) between low and high RFI steers, on the RD and CD, respectively. ME for maintenance (MEm; kg .75 d–1) and the partial efficiencies of ME used for maintenance and gain were similar for low and high RFI steers. Likewise, no differences were found in fasting HP or fed HP. Motion activity was lower (P < 0.05) for low RFI steers compared to high RFI steers during fasting HP. Covariate analysis of HP at the same activity level yielded similar results. At slaughter, weights of lung and trachea (P < 0.05), spleen (P < 0.05) and adrenal gland (P = 0.07) were higher for low RFI cattle. The lack of differences in energy partitioning between divergent RFI steers may have been the result of alterations in feeding behavior or stress imposed by adapting steers to calorimetry chambers.

With feed costs representing on average 65% of the total cost of production improvements in feed efficiency could have a major impact on the beef industry. Postweaning performance and feed efficiency data were collected on 114 heifers born on the University of Arizona's V bar V Ranch. Residual feed intake (RFI) was significantly correlated with dry matter intake (DMI) (r = 0.46) and G:F (r = -0.43), while G:F was moderately correlated with initial age (r = -0.54), initial body weight (r = -0.40), and average daily gain (ADG) (r = 0.68). Residual gain (RG) was moderately correlated with RFI (r = -0.41) and highly correlated with ADG (0.62) and G:F (0.73). In addition, RG was significantly correlated (r = -0.21) with initial weight suggesting that selection for RG could lead to increased cow mature size. Heifers were sorted into three breed categories: Hereford, Hereford cross, and Wagyu cross and breed effect on performance and feed efficiency traits were analyzed. Significant differences in DMI, FCR, and RG were noted, but likely due to significant differences in age at the time of testing. RFI was not significantly different between breed groups, suggesting that RFI is less influenced by animal age than other measures of feed efficiency. In addition, sires of study heifers with 5 or more progeny were selected and progeny performance and feed efficiency traits were compared between sires. No significant differences in ADG, RFI, FCR, or RG were noted between sire progeny. This was likely due to an insufficient number of progeny used in the trial. Further research and an increased number of animals used may uncover significant impacts of sire on RFI.

The 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.

The 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.

Residual feed intake (RFI) is a recognized measure of biological efficiency in beef cattle. However, RFI determination is expensive, time consuming and not well studied in animals fed forage-based diets. The objectives of this experiment were to investigate infrared thermography (IRT) as method for determining RFI ranking in yearling beef bulls, and to evaluate the effect of diet type on RFI repeatability in consecutive feeding periods. No significant correlations (P > 0.05) were observed between eye or cheek surface temperatures measured using handheld or within-pen stationary infrared camera systems with RFI. Reranking was observed for RFI in all diet treatments, however significant repeatability estimates occurred for the forage and grain diet treatments (r=0.58 and 0.64 respectively; P < 0.01) but not the diet switch treatment (r=0.24; P > 0.05). Extreme cold temperatures experienced in Western Canada influence IRT measurements and energy partitioning, indicating the need for standardized performance testing procedures. / February 2016

No description available.

O interesse quanto ao uso de índices de eficiência alimentar na seleção de bovinos é crescente, pela sua associação com o custo de produção e impacto ambiental. O objetivo deste trabalho foi avaliar dois índices de eficiência, o consumo alimentar residual (CAR) e consumo e ganho residual (CGR) e suas relações com desempenho, características de carcaça, qualidade de carne, batimentos cardíacos e consumo de oxigênio em bovinos Nelore. Foram avaliados 84 animais para desempenho, peso de carcaça, rendimento, área de olho de lombo, espessura de gordura subcutânea, peso de vísceras e gordura interna. Foi avaliada a qualidade da carne de amostras não maturadas e maturadas (pH, força de cisalhamento, cor, perdas por cocção, capacidade de retenção de água, índice de fragmentação miofibrilar e gordura intramuscular). Para estimar a produção de calor (PC) pela metodologia do Pulso de O2 (O2P), 39 animais foram monitorados para frequência cardíaca, que foi calibrada para consumo de O2 em 18 deles. A PC foi estimada multiplicando-se o total de batimentos cardíacos diários pelo volume de O2/batimento e pela constante 4,89 kcal/LO2. Foram estudados os coeficientes de inclinação das retas entre CAR e CGR e as variáveis estudadas. O CAR não foi associado com o peso vivo e ganho de peso (P>0,05), porém animais eficientes consumiram 16,1% menos alimento (P<0,0001). Animais eficientes para CGR apresentaram consumo 11,7% menor e ganharam mais peso (P<0,01). O CGR não foi associado ao peso vivo metabólico médio (P>0,05), contudo foi associado ao peso vivo final (P=0,06). A PC estimada pela diferença entre energia retida e consumo de energia metabolizável foi maior nos animais ineficientes (P<0,0001), porém não foi diferente quando estimada pela metodologia do O2P (P>0,05). A frequência cardíaca (FC) e consumo de O2 não foram associados ao CAR e CGR (P>0,05), contudo a FC foi menor nos animais eficientes durante a calibração do O2 (P<0,05). Ambos os índices foram associados com mudanças na composição corporal; animais eficientes para CAR apresentaram menor teor de gordura subcutânea avaliada por ultrassom (P=0,08), e os eficientes para CGR apresentaram maior AOL (P<0,05). As características de qualidade da carne não foram associadas ao CAR, mas animais eficientes para CGR apresentaram intensidade da cor vermelha na carne menor e na gordura maior (P<0,05). Animais eficientes quanto ao CAR apresentaram menor peso de fígado e de gordura interna (P<0,05) sendo este efeito não observado para CGR. Os animais eficientes em ambos, CAR e CGR, apresentaram menor custo de produção resultando em aumento no lucro (P<0,01). O lucro foi fortemente associado à conversão alimentar, CGR e ganho de peso (r=-0,812; 0,72 e 0,61; P<0,0001) enquanto sua associação com CAR foi menor (r=-0,46; P<0,0001). As correlações fenotípicas sugerem que seleção de animais eficientes para CAR ou CGR pode reduzir custos na produção de bovinos de corte, com alteração na coloração da carne. O lucro tem maior correlação com o CGR que com CAR. Porém o CGR tem a possível desvantagem de ser fenotipicamente associado ao maior peso final o que pode indicar uma correlação genética para peso adulto. / There is growing interest in the use of feed efficiency in beef cattle, due to its relationship to production costs and environmental impact. Identification of variation in energy losses can explain differences in efficiency. The objective of this study was to evaluate measures of feed efficiency (residual feed intake - RFI and residual intake and gain _ RIG) and their relationships with performance, carcass characteristics, meat quality, heart rate and oxygen use in Nellore bulls. A group of 84 animals were evaluated for performance, carcass characteristics (weight, yield, loin eye area, fat thickness, weight of visceral and internal fat) and meat quality in fresh and aged meat samples (pH, shear force, cooking loss, water retention capacity, myofibrilar fragmentation index and intramuscular fat). To estimate heat production (HP) by O2 pulse methodology (O2P), 39 animals were monitored for heart rate (HR). A subgroup of 18 animals which was calibrated for O2 consumption determined over in 18 of them. HP was estimated multiplying daily heart beats by O2 volume per beat, assuming 4.89 kcal/LO2 as constant. The slope coefficient for each variable against RFI and RIG was studied. There was no association of RFI with weight (P>0.05) and weight gain (P>0.05), but efficient animals consumed 16.1% less feed (P<0.0001). Efficient animals for RIG consumed 11.7% less food (P<0.0001), but gained more weight than inefficient animals (P<0.01). There was no association between RIG and average metabolic weight (P>0.05), however RIG was related to final weight (P=0.06). HP estimated by the difference between retained energy and metabolic energy intake was higher for inefficient animals (P<0.001), for both RFI and RIG. However there was no effect on HP estimated by the O2P methodology (P>0.05). Heart rate (HR) and O2 consumption were not associated with RFI and RIG (P>0.05), but HR was lower in efficient animals during O2 calibration (P<0.05). There was a positive association of efficiency with a leaner gain composition, where efficient animals for RFI had of lower ultrasound subcutaneous fat (P=0.08), while efficient animals for RIG had higher loin eye area (P<0.05). There was no effect on meat quality parameters for RFI but in efficient animals for RIG, there was an effect on meat and fat color (P<0.05) compared to inefficient animals. Internal fat and liver weights were decreased in efficient animals according to RFI (P<0.05), but unchanged according to RIG (P>0.05). Efficient animals for RFI and RIG had lower cost of production resulting in increased profit (P<0.01). Profit was strongly associated with feed intake, RIG and weight gain (r =-0.81, 0.72 and 0.61, P<0.0001), whereas its association with RFI was lower (r =-0.46, P<0.0001). Efficient animals for RFI and RIG are more profitable with small decreases in fat and small increases in muscle content. Profit is better related to RIG than RFI. However, RIG had the disadvantage of increasing final test weight which could be genetically associated with mature weight.

O interesse quanto ao uso de índices de eficiência alimentar na seleção de bovinos é crescente, pela sua associação com o custo de produção e impacto ambiental. O objetivo deste trabalho foi avaliar dois índices de eficiência, o consumo alimentar residual (CAR) e consumo e ganho residual (CGR) e suas relações com desempenho, características de carcaça, qualidade de carne, batimentos cardíacos e consumo de oxigênio em bovinos Nelore. Foram avaliados 84 animais para desempenho, peso de carcaça, rendimento, área de olho de lombo, espessura de gordura subcutânea, peso de vísceras e gordura interna. Foi avaliada a qualidade da carne de amostras não maturadas e maturadas (pH, força de cisalhamento, cor, perdas por cocção, capacidade de retenção de água, índice de fragmentação miofibrilar e gordura intramuscular). Para estimar a produção de calor (PC) pela metodologia do Pulso de O2 (O2P), 39 animais foram monitorados para frequência cardíaca, que foi calibrada para consumo de O2 em 18 deles. A PC foi estimada multiplicando-se o total de batimentos cardíacos diários pelo volume de O2/batimento e pela constante 4,89 kcal/LO2. Foram estudados os coeficientes de inclinação das retas entre CAR e CGR e as variáveis estudadas. O CAR não foi associado com o peso vivo e ganho de peso (P>0,05), porém animais eficientes consumiram 16,1% menos alimento (P<0,0001). Animais eficientes para CGR apresentaram consumo 11,7% menor e ganharam mais peso (P<0,01). O CGR não foi associado ao peso vivo metabólico médio (P>0,05), contudo foi associado ao peso vivo final (P=0,06). A PC estimada pela diferença entre energia retida e consumo de energia metabolizável foi maior nos animais ineficientes (P<0,0001), porém não foi diferente quando estimada pela metodologia do O2P (P>0,05). A frequência cardíaca (FC) e consumo de O2 não foram associados ao CAR e CGR (P>0,05), contudo a FC foi menor nos animais eficientes durante a calibração do O2 (P<0,05). Ambos os índices foram associados com mudanças na composição corporal; animais eficientes para CAR apresentaram menor teor de gordura subcutânea avaliada por ultrassom (P=0,08), e os eficientes para CGR apresentaram maior AOL (P<0,05). As características de qualidade da carne não foram associadas ao CAR, mas animais eficientes para CGR apresentaram intensidade da cor vermelha na carne menor e na gordura maior (P<0,05). Animais eficientes quanto ao CAR apresentaram menor peso de fígado e de gordura interna (P<0,05) sendo este efeito não observado para CGR. Os animais eficientes em ambos, CAR e CGR, apresentaram menor custo de produção resultando em aumento no lucro (P<0,01). O lucro foi fortemente associado à conversão alimentar, CGR e ganho de peso (r=-0,812; 0,72 e 0,61; P<0,0001) enquanto sua associação com CAR foi menor (r=-0,46; P<0,0001). As correlações fenotípicas sugerem que seleção de animais eficientes para CAR ou CGR pode reduzir custos na produção de bovinos de corte, com alteração na coloração da carne. O lucro tem maior correlação com o CGR que com CAR. Porém o CGR tem a possível desvantagem de ser fenotipicamente associado ao maior peso final o que pode indicar uma correlação genética para peso adulto. / There is growing interest in the use of feed efficiency in beef cattle, due to its relationship to production costs and environmental impact. Identification of variation in energy losses can explain differences in efficiency. The objective of this study was to evaluate measures of feed efficiency (residual feed intake - RFI and residual intake and gain _ RIG) and their relationships with performance, carcass characteristics, meat quality, heart rate and oxygen use in Nellore bulls. A group of 84 animals were evaluated for performance, carcass characteristics (weight, yield, loin eye area, fat thickness, weight of visceral and internal fat) and meat quality in fresh and aged meat samples (pH, shear force, cooking loss, water retention capacity, myofibrilar fragmentation index and intramuscular fat). To estimate heat production (HP) by O2 pulse methodology (O2P), 39 animals were monitored for heart rate (HR). A subgroup of 18 animals which was calibrated for O2 consumption determined over in 18 of them. HP was estimated multiplying daily heart beats by O2 volume per beat, assuming 4.89 kcal/LO2 as constant. The slope coefficient for each variable against RFI and RIG was studied. There was no association of RFI with weight (P>0.05) and weight gain (P>0.05), but efficient animals consumed 16.1% less feed (P<0.0001). Efficient animals for RIG consumed 11.7% less food (P<0.0001), but gained more weight than inefficient animals (P<0.01). There was no association between RIG and average metabolic weight (P>0.05), however RIG was related to final weight (P=0.06). HP estimated by the difference between retained energy and metabolic energy intake was higher for inefficient animals (P<0.001), for both RFI and RIG. However there was no effect on HP estimated by the O2P methodology (P>0.05). Heart rate (HR) and O2 consumption were not associated with RFI and RIG (P>0.05), but HR was lower in efficient animals during O2 calibration (P<0.05). There was a positive association of efficiency with a leaner gain composition, where efficient animals for RFI had of lower ultrasound subcutaneous fat (P=0.08), while efficient animals for RIG had higher loin eye area (P<0.05). There was no effect on meat quality parameters for RFI but in efficient animals for RIG, there was an effect on meat and fat color (P<0.05) compared to inefficient animals. Internal fat and liver weights were decreased in efficient animals according to RFI (P<0.05), but unchanged according to RIG (P>0.05). Efficient animals for RFI and RIG had lower cost of production resulting in increased profit (P<0.01). Profit was strongly associated with feed intake, RIG and weight gain (r =-0.81, 0.72 and 0.61, P<0.0001), whereas its association with RFI was lower (r =-0.46, P<0.0001). Efficient animals for RFI and RIG are more profitable with small decreases in fat and small increases in muscle content. Profit is better related to RIG than RFI. However, RIG had the disadvantage of increasing final test weight which could be genetically associated with mature weight.

ABSTRACT: Study One - Our objective was to characterize mature range cows based on intake and grazing activity. Starting in the early spring of 2013, 4 experiments were conducted. First, mature range cows (n = 137) were fitted with radio frequency identification tags (RFID) and placed in a dry-lot pen equipped with GrowSafe® technology to monitor DMI of alfalfa hay. These data were then used to assign cows a residual feed intake (RFI) value utilizing the National Research Council (NRC) (1996) model to predict intake of beef cattle. Cattle with negative and positive RFI were characterized as low-intake and high-intake, respectively. In addition, the following data were also recorded: weight (kg), age (mo), days pregnant (d), and body condition score (BCS). Second, 30 mature range cattle were selected from the first trial and fitted with pedometers for 7 d to monitor activity with step counts and estimate distance traveled. Third, mature range cows (n = 25) selected from the first trial were fitted with global position system (GPS) collars, and placed on pinyon-juniper rangeland from 20 June 2014 to 17 September 2014. Forth, mature range cows (n = 28) were fitted with GPS collars, and placed on ponderosa pine rangeland from 17 September 2014 to 15 October 2014. Distance traveled, slope, distance from water, elevation data were collected from both GPS trials. Low-intake and high-intake cows consumed 9.3 and 12.2 kg/d, respectively (P < 0.0001). Low-intake cattle became pregnant sooner (P = 0.002) than high-intake cattle (average of 16 d sooner). Cattle age (mo) equaled 90 and 98 for low- and high-intake cows, respectively (P = 0.04). Weight, predicted DMI, and BCS did not differ between groups (P > 0.06). Step counts for low- and high-intake animals were 5839 and 5383 ± 2089, respectively (P = 0.61), and estimated distance traveled was 4.31 and 5.35 ± 1.66 km d⁻¹ for low- and high-intake animals, respectively (P = 0.77). Low-intake cows (6.23 km d⁻¹) traveled farther (P = 0.005) each day than high-intake cows (5.84 km d⁻¹) on pinyon-juniper rangelands, and high-intake cows utilized (P = 0.013) steeper slopes. No differences were detected (P ≥ 0.06) for distance traveled, distance from water, and elevation for cows grazing ponderosa pine rangeland). However, low-intake cattle preferred (P = 0.046) steeper slopes on ponderosa pine rangeland than high-intake cattle. These results indicate that low-intake animals may travel farther on some rangelands and rebreed earlier. Study Two - Commercial grade heifers (n = 173) born and raised on the University of Arizona's V bar V Ranch from 2012 to 2014 were fitted with radio frequency identification tags (RFID) and placed in a drylot equipped with Growsafe® technology (8 bunks) for 60 d in 3 groups based on birth year in order to calculate DMI, residual feed intake (RFI), ADG, G:F, and residual gain (RG). Birth date, birth weight, weaning weight, age at start of trial, initial trial weight, and final trial weights were also recorded. Residual feed intake scores were utilized to place heifers in one of three treatment groups, low-, medium-, and high-intake. Reproductive and calf data were collected on heifers born in 2012. Means for birth date, birth weight, weaning weight, initial weight, final weight, and ADG did not differ among the three treatments. Residual gain for low-, medium-, and high-intake heifers were different (P < 0.05) at 0.07, 0.00, and -0.07 kg d⁻¹, respectively. Low-intake cattle had an improved (P < 0.05) GF ratio of 0.19 when compared to the medium- and high-intake heifers with ratios of 0.15 and 0.13 (P > 0.05), respectively. Differences (P <0. 05) in DMI were detected with low-, medium, and high-intake heifers consuming 5.2, 6.2, and 7.5 kg d⁻¹, respectively. No differences were detected for pregnancy rate, calving rate, percent bred artificial insemination (AI), percent bull calves, calf birth weight, and calf birth date among treatments (P > 0.05).Study Three - Commercially available GPS tracking collars for cattle are cost prohibitive to most researchers. This paper will present a low-cost alternative to those collars (Knight GPS tracking collars), and provide detailed instructions on where to source materials and how to fabricate inexpensive GPS tracking collars. In addition, the two types of collars will be compared in a study where Brangus cattle (n = 8) were each fitted with LOTEK® 3300 and Knight GPS tracking collars for 31 d beginning 14 March 2015 at the Chihuahuan Desert Rangeland Research Center (CDRRC) 37 km north of Las Cruces, New Mexico. Location, slope, distance from water, distance traveled and elevation were recorded every 10 min. A record of GPS fix rate was logged. No differences were detected (P≥0.369) between collar types for location, slope, or distance from water. However, there was a tendency (P = 0.08) for Knight collars to report a lower estimate for distance traveled at 6171 m d⁻¹ compared to Lotek collars at 7104 m d⁻¹. Fix rate was greater (P≤0.001) for Lotek collars compared to Knight collars at 99.9 and 66.2%, respectively. Study Four - Previously characterized commercial cows (n = 26) were placed into either high (positive RFI) or low intake (negative RFI) groups. On 14 May 2015, 13 high- and 13 low-intake cows were fitted with modified igotU GT-120® GPS logging collars. Cattle were then placed on rangeland for 120 d. The first 30 d period animals transitioned from desert shrubland to pinyon-juniper. From 31 to 60 d, animals grazed pinyon-juniper rangeland. Next, during days 61 to 90, animals transitioned from pinyon-juniper to ponderosa pine, and the last 30 d were spent in ponderosa pine. Time periods will be referred to as month 1, 2, 3, and 4 for days 0 to 30, 31 to 60, 61 to 90, and 91 to 120, respectively. Location, slope, distance from water, elevation, and time spent close to water were recorded every 10 min. No differences were observed in the utilization of elevation or distance traveled, or distance from water (P>0.05). Low intake animals used a higher maximum slope (P < 0.05) during month 3, but slope utilization differences were not detected for other portions of the trial (P > 0.05). Study Five - Hereford sires (n = 35) with 7 or more cow offspring on the University of Arizona V bar V ranch in Rimrock, Arizona were tested at Neogen laboratories in Lincoln, NE for an Igenity Gold genetic profile. Their residual feed intake (RFI), ADG, tenderness, marbling score, milk production percent choice, yield grade, fat thickness, ribeye area, heifer pregnancy rate, stayability, maternal calving ease, birthweight and docility were estimated. Sires were given a genetic RFI score based on their RFI profile and placed into one of three intake groups, low (< 0.5 SD), medium (± 0.5 SD) and high (> 0.5 SD). Performance traits of cow offspring (n = 839) from those sires were also compared based on their sire's intake group. No differences (P > 0.05) were detected among sire intake groups for ADG, tenderness, marbling score, percent choice, yield grade, fat thickness, ribeye area, heifer pregnancy rate, stayability, maternal calving ease, birthweight and docility. Residual feed intake differed among groups (P < 0.05), and high intake cattle had more estimated milk production compared to low intake animals (P < 0.05). Cows from low intake sires were born later in the year (P < 0.05). High intake cattle had a higher (P < 0.05) birthweight and survived longer (P < 0.05) in the herd when compared to low and medium intake cows. Genetic RFI and expected milk production were moderately to highly correlated.

Residual Feed Intake (RFI) and enteric methane (CH4) emissions were measured over two years on 120 Angus bulls receiving either a silage-hay diet or a silage-grain diet (277±28 and 286±25 d of age in year 1; 249±23 and 250±23 d of age in year 2). Emissions were similar between diets (240 vs. 248  7.9 L d-1, P>0.05; silage-hay vs. silage-grain) and RFI grouping (P>0.05). DMI increased for high RFI bulls versus low RFI bulls (7.68±0.2 and 8.24±0.2 kg DM d-1, low vs. high). Correlations between RFIfat and CH4 emissions were not significant. These findings agree with previous studies and suggest that RFI ranking may be associated with metabolic mechanisms other than fermentation efficiency. / October 2016