The phenotypic relationship between residual intake and gain and other feed efficiency traits in Nellore cattle

This study aimed to compare feed efficiency measures of Nellore beef cattle on different residual intake and gain (RIG) classes. We used data from 610 animals weighing on average 236.33 kg and average of 283 days of age from feedlot performance tests carried out between 2005 and 2012. Animals were grouped based on RIG into three different classes: high RIG (>?mean?+?0.5 standard deviation (SD), most efficient; n?=?193), medium RIG (mean?±?0.5 SD; n?=?235), and low RIG (<?mean – 0.5 SD, least efficient; n?=?182). Residual feed intake (RFI), residual gain (RG), feed conversion ratio (FCR), feed efficiency (FE), relative growth rate (RGR), and Kleiber ratio (KR) of animals in each RIG class were compared by Tukey test at 1% of probability. Phenotypic correlations between variables were evaluated as well. Animals on high RIG class showed lower dry matter intake (P?<?0.01) and higher average daily gain (P?<?0.01) than low RIG animals. Consequently, high RIG animals had lower FCR (P?<?0.01) and higher FE (P?<?0.01) than those animals in low RIG class. The most efficient animals based on RIG were also the most efficient animals based on RG and RFI. RIG was negatively correlated to dry matter intake (P?<?0.01) and FCR (P?<?0.01), and a positive correlation was found between RIG and FE (P?<?0.01). Therefore, RIG appears to be a good parameter to select animals with reduced dry matter intake and high productive performance.

     

Phenotypic and genetic relationships between residual energy intake and growth, feed intake, and carcass traits of young bulls.

Residual energy intake, defined as actual minus predicted energy intake during a production period, was estimated for each of 650 bull calves of 31 Holstein Friesian or Brown Swiss sires. Residual energy intake, measured under ad libitum feeding, had heritabilities similar to those of growth rate and energy conversion ratio with an estimate of approximately .3. Residual energy intake was related to average daily energy intake both phenotypically and genetically such that selection for decreased residual energy intake would lead to a decrease in daily feed intake. Such selection would also tend to increase carcass fatness (i.e., genetically fat animals are the most efficient). Residual energy intake estimated with and without correction for carcass composition were closely correlated. Thus, residual energy intake may be estimated without the knowledge of carcass composition in growing bulls of dual-purpose breeds.     

Comparison and relation among different estimates of residual feed intake for Japanese Black (Wagyu) bulls

Residual feed intake (RFI) was estimated by ordinary regression (RFI_ord), linear regression (RFI_reg), and genetic regression (RFI_gen) for Japanese Black bulls, and compared among them by the magnitude of correlations, heritabilities, and empirical mean squared errors. The estimations were made for a total test periods of 140 days (77 bulls) and 112 days (663 bulls) sub‐divided each into two equal stages: first half and second half of the test periods. The means of RFI_reg, RFI_ord, and RFI_gen for the total test periods were 1.09, ?0.05, and ?2.21 kg/day, respectively. The genetic variation exists for these estimates at different stages of the test period. High genetic and phenotypic correlations (>0.95) were found between RFI_ord and RFI_gen, confirming that these are regarded practically as the same traits. The phenotypic variance (0.714) and heritability (0.24) of RFI_ord were close to those of RFI_gen (0.726 and 0.25, respectively). According to the empirical mean squared errors from the result of the total test periods, RFI_gen yielded better estimates of RFI. The high to moderate heritabilities for RFI_ord were estimated for the three stages of the test periods, indicating that RFI_ord might be an alternative estimate for genetic improvement of feed utilization.     

Relationship between body measurements,metabolic hormones,metabolites and residual feed intake in performancetested pedigree beef bulls

The objective of this study was to examine the relationship between easily measured, potential physiological and physical indicators of feed efficiency including metabolic hormones, metabolites, ultrasonic muscle and fat measures with performance and efficiency traits in performance tested pedigree beef bulls (n = 302; initial bodyweight 493 (SD = 64) kg). Animals were offered a high energy concentrate ad libitum plus 1.5 kg fresh weight grass hay daily and individual feed intake was measured for 70 days. Blood samples were collected by coccygeal venipuncture at the start and end of the performance test period and analysed for plasma concentrations of IGF-I, insulin, leptin and various metabolites. Similarly, ultrasonic muscle and fat depths were measured at the start and end of the test period. Residual feed intake (RFI) was computed for each animal as the residuals from a multiple regression model regressing dry matter intake (DMI) on average daily gain (ADG) and mid-test BW^0.75 (MWT). Overall ADG, DMI, feed:gain (F:G) and RFI were 1.91 (SD = 0.29), 10.10 (SD = 1.31), 5.37 (SD = 0.84) and 0.00 (SD = 0.78), respectively. Residual feed intake was strongly correlated with DMI (r = 0.67) and moderately correlated with F:G (r = 0.40). Moderate positive correlations ranging from 0.3 to 0.6 were estimated between ultrasonic measures of final fat and muscle depth and their respective gains over the test period with DMI, ADG and RFI. There was no evidence of a strong association between any of the plasma analytes measured and RFI at either sampling times. However, end of test insulin was negatively correlated (r = − 0.14) with RFI. Final IGF-I concentration was negatively associated with DMI (r = − 0.14) and F:G (r = − 0.15). End of test circulating leptin concentration was positively correlated with DMI (r = 0.14) and F:G (r = 0.15). Plasma glucose concentration at the end of test was negatively related to DMI (r = − 0.21) and F:G (r = − 0.21). A positive relationship was observed between end of test plasma urea concentration and DMI (r = 0.30). Overall, the correlation coefficient estimates between the potential blood markers and measures of intake, performance and efficiency were weak and generally not different from zero. This suggests that it is unlikely that measurement of these metabolic indicators, per se, will be useful in the early identification of feed efficient animals.     

The relationship between residual feed intake and feed intake behavior in group-housed Duroc barrows

Because feed is the major input in pork production, conversion of feed into lean tissue at minimum costs has been a focus for improvement. Several researchers have proposed using residual feed intake (RFI) rather than feed conversion ratio (FCR) for genetic improvement of feed efficiency. Little is known about the variation in RFI in pigs. As several studies suggest a greater RFI is related to greater animal activity levels, the current study investigated the phenotypic relationship between RFI and feed intake (FI) behavior of 104 group-housed growing Duroc barrows allowed ad libitum access to feed. Feed intake, BW gain, feeding time (TIME), feeding frequency (VISITS), RFI, and FCR were calculated for 5 periods of 14, 23, 28, 21, or 23 d in length (periods 1 through 5, respectively) on animals that were between 73 to 95 d of age at the start of the testing period. Barrows that grew faster consumed more feed (P < 0.001), and barrows that consumed more feed were fatter (P < 0.01). There were no correlations between VISITS and TIME, between VISITS and FI, or between VISITS and RFI. Barrows that spent more time at the feeder, however, consumed more feed (P < 0.05) and had greater RFI in periods 1, 3, and 5 (P < 0.05). As expected, FI and FCR were highly correlated with RFI (P < 0.001). These results suggest that a greater FI rather than greater feed intake activity resulted in greater RFI values.     

Impact of selection for residual feed intake on breeding soundness and reproductive performance of bulls on pasture-based multisire mating

There is concern in the beef industry that selecting bulls for feed efficiency based on residual feed intake (RFI) may have a negative impact on bull reproductive performance and fertility. Here we investigated the impact of selection of bulls for low RFI on breeding soundness evaluation (BSE), reproductive performance, and fertility of bulls under natural service in multisire mating groups on pasture. Of the 412 RFI-tested bulls available, 98 (23.8%) were culled for performance, type, temperament, or other reasons, and 88 (21.4%) were culled for failing BSE, for an overall cull rate of 45.1%. From among the 314 bulls subjected to BSE, 32 (10.2%), 20 (6.4%), and 36 (11.4%) were culled for poor feet and legs, scrotal circumference, and semen quality, respectively. The BSE traits were not different (P > 0.10) between bulls categorized as either inefficient (+RFI) or efficient (-RFI), but the proportion of bulls that failed to meet the 60% minimum sperm motility requirement tended (P = 0.07) to be greater in the -RFI group than in the +RFI group (10.2% vs. 4.4%, respectively). In a subpopulation of 115 bulls, individual progressive sperm motility was greater (P < 0.05) in +RFI (85%) than -RFI (80%) bulls. A multisire natural mating experiment was conducted during 2 consecutive breeding seasons (2006 to 2007 and 2007 to 2008) using 18 +RFI and 18 -RFI bulls. The overall calving rate (calves born/cows exposed) was 72.9%. Mean number of progeny per sire was significantly greater (P < 0.01) in -RFI bulls (18.3) than in +RFI bulls (11.8). Selection for feed efficiency based on RFI appears to have no detrimental impact on reproductive performance and fertility in beef bulls bred in multisire groups on pasture. However, the decreased sperm motility and the greater number of progeny per sire associated with -RFI status need further investigation.     

Performance, growth, and maturity of Nellore bulls

The objectives of this study were to evaluate the dry matter intake (DMI), digestibility, average daily gain (ADG), microbial efficiency, empty body weight (EBW) gain, and body composition of Nellore bulls. Additionally, Nellore bull maturity was estimated, and the prediction equation for DMI, suggested by the Brazilian nutrient requirements system (BR CORTE; Azevêdo et al. 2010), was evaluated. Thirty-three Nellore bulls, with a mean initial weight of 259?±?25 kg and age of 14?±?1 months, were used in this study. Five animals were slaughtered at the beginning of the experiment (control group), and the remaining 28 were divided into 4 groups, each slaughtered at 42-day intervals. Their diet was composed of corn silage and concentrate (55:45). The power model was used to estimate muscle tissue, bone tissue, crude protein (CP), mineral matter (MM), and water present in the empty body, while the exponential model was used to estimate adipose tissue and ether extract (EE) present in the empty body. When expressed in kilograms per day, differences were observed (P?<?0.05) only for the intake of EE and neutral detergent fiber as a function of feedlot time periods. Although there was a difference in relation to nutrient intake, it did not affect (P?>?0.05) digestibility, with the exception of EE digestibility. The equation suggested by BR CORTE correctly estimates the DMI of Nellore bulls. ADG was not affected (P?>?0.05) by time spent in the feedlot. No differences were observed (P?>?0.05) for microbial efficiency; a mean value of 142 g microbial crude protein/kg total digestible nutrients was achieved. The muscle and bone tissues, CP, MM, and water present in the empty body increased as the animal grew, although at a lower rate. The adipose tissue and EE present in the empty body increased their deposition rate when the animal reached its mature weight. Maturity is defined as when an animal reaches 22 % EE in the empty body, which corresponds to 456 kg of EBW in Nellore bulls. Therefore, this study can conclude that the feedlot time period does not affect DMI, nutrient intake, ADG, or microbial efficiency. The equation proposed by BR CORTE (Azevêdo et al. 2010) correctly estimates the DMI of Nellore bulls, which reach maturity when an EBW of 456 kg is attained.     

Effect of selection for residual feed intake on feeding behavior and daily feed intake patterns in Yorkshire swine

Residual feed intake (RFI) is a measure of feed efficiency defined as the difference between observed and predicted feed intake based on average requirements for growth and maintenance. The objective of this study was to evaluate the effect of selection for decreased RFI on feeding behavior traits and to estimate their relationships with RFI. Three data sets from the 4th and 5th generations of a selection experiment with a line selected for reduced RFI (LRFI) and a randomly selected control line (CTRL) were analyzed. Lines were mixed in pens of 16 and evaluated for feeding behavior traits obtained from a single-space electronic feeder over a growing period of ~3 mo before ~115 kg. The following traits were evaluated as averages over the entire test period and over the first and second half of the test period: number of visits per day and hour; occupation time per day, visit, and hour; feed intake (FI) per day, visit, and hour; and FI rate per visit. Models used included fixed effects of line and feeder, covariates of on-test age and FI per day, and random effects of pen, on-test group, sire, and litter. Repeated measures models were used to analyze feeding patterns during the day. The LRFI pigs had significantly less FI per day than CTRL pigs for all 3 data sets. With adjustment for FI per day, line differences of all traits were in the same direction for all 3 data sets but differed in significance and size. Feed intake per visit and hour and visits per day and hour did not differ between lines, but the trend was for LRFI pigs to have fewer visits, in particular during peak eating times. The LRFI pigs had a greater feeding rate and less occupation time per day, visit, and hour than CTRL pigs, but this was not significant for all data sets. Correlations of RFI with FI per day and visit and visits per day were positive. Average daily gain was positively correlated with FI per day and visit and occupation time per visit but negatively correlated with visits per day. Feed intake per day was positively correlated with backfat. In conclusion, feed efficiency may be affected by FI behavior because selection for decreased RFI has resulted in pigs that spend less time eating and eat faster.     

Inclusive inheritance for residual feed intake in pigs and rabbits

Non-genetic information (epigenetic, microbiota, behaviour) that results in different phenotypes in animals can be transmitted from one generation to the next and thus is potentially involved in the inheritance of traits. However, in livestock species, animals are selected based on genetic inheritance only. The objective of the present study was to determine whether non-genetic inherited effects play a role in the inheritance of residual feed intake (RFI) in two species: pigs and rabbits. If so, the path coefficients of the information transmitted from sire and dam to offspring would differ from the expected transmission factor of 0.5 that occurs if inherited information is of genetic origin only. Two pigs (pig1, pig2) and two rabbits (rabbit1, rabbit2) datasets were used in this study (1,603, 3,901, 5,213 and 4,584 records, respectively). The test of the path coefficients to 0.5 was performed for each dataset using likelihood ratio tests (null model: transmissibility model with both path coefficients equal to 0.5, full model: unconstrained transmissibility model). The path coefficients differed significantly from 0.5 for one of the pig datasets (pig2). Although not significant, we observed, as a general trend, that sire path coefficients of transmission were lower than dam path coefficients in three of the datasets (0.46 vs 0.53 for pig1, 0.39 vs 0.44 for pig2 and 0.38 vs 0.50 for rabbit1). These results suggest that phenomena other than genetic sources of inheritance explain the phenotypic resemblance between relatives for RFI, with a higher transmission from the dam's side than from the sire's side.     

Bayesian analysis of the effect of selection for residual feed intake on growth and feed intake curves in Yorkshire swine

Gompertz growth functions were fitted to longitudinal measurements of daily feed intake (DFI) and BW of 586 boars and 495 gilts from a selection experiment in Yorkshire pigs for residual feed intake (RFI). The selection experiment consists of a line selected for low residual feed intake (LRFI) for 5 generations and a randomly selected control line (CTRL). The objectives of this study were to use Bayesian methods to estimate genetic parameters of the Gompertz curve parameters for DFI and BW, to evaluate the effect of selection for reduced RFI on the Gompertz parameters and shape of curves for DFI and BW, and to develop methodology for quantifying genetic variation at the level of the original phenotypes for DFI and BW based on the Bayesian analysis of the nonlinear model. Separate analyses were done for boars and gilts and for BW and DFI. A hierarchical model was specified in 2 levels: in the first level, the Gompertz function was modeled for each pig, and at the second level, a 3-trait linear mixed model was fitted to the 3 Gompertz parameters (asymptotic value, inflection point, and decay parameter), with fixed effects of line by generation and random effects of additive genetic and environmental effects. Bayesian methods were used to combine the 2 levels of modeling. A total of 30,000 random samples of the posterior distributions after convergence of Markov chains were used for inference. Posterior means of heritability within the first level of the model for the asymptotic value, inflection point, and decay parameter for DFI were 0.74, 0.66, and 0.82 for boars and 0.79, 0.70, and 0.57 for gilts; corresponding estimates for BW were 0.64, 0.58, and 0.60 for boars and 0.46, 0.35, and 0.33 for gilts. For DFI, LRFI boars had a reduced mature DFI (2.91 vs. 3.20 kg/d) and an earlier inflection point (85 vs. 95 d) compared with CTRL boars. For BW, LRFI boars had a lighter mature BW (279 vs. 317 kg), an earlier inflection point (184 vs. 198 d), and a decreased decay parameter (127 vs. 134 d) compared with CTRL boars. In contrast, LRFI gilts had a later inflection point (225 vs. 200 d) and a greater decay parameter (172 vs. 143 d) than CTRL gilts for BW. The other Gompertz curve parameters for DFI and BW for boars and gilts were considered not different between lines, with posterior probabilities of the line differences being greater than zero ranging from 0.1 to 0.9.     

Evidence of residual feed intake reranking in crossbred replacement heifers

The objective of the study was to examine whether residual feed intake (RFI) reranking exists between 2 consecutive periods in replacement heifers fed the same diet. The study collected feed intake and BW data from 190 crossbred heifers over a 3-yr period (61 in 2007, 68 in 2008, and 61 in 2009) during the winter-spring season. The heifers were fed a roughage-based diet (90% barley silage and 10% rolled barley grain) throughout the feeding trial, which was broken down into 2 feeding periods with ADG of 0.94 and 0.90 kg?d(-1) in the first and second periods, respectively. The RFI was calculated for the entire period using different models, which included ADG, mid-metabolic BW, body composition, and feeding activity. Gain:feed ratio and Kleiber ratio were also calculated. Rank correlations among the RFI calculated from different models were obtained, as well as rank correlations between the 2 feeding periods for the feed efficiency measures. Including body composition and feeding activity only improved the R(2) by 1 to 5%. The rank correlations among the different models were high (90 to 95%) for RFI calculated for the entire feeding period. However, the RFI calculated within the second feeding period had greater rank correlation than the RFI calculated from the entire feeding period. Compared with G:F and Kleiber ratio, RFI gave lesser reranking between periods 1 and 2. About 49% of the heifers maintained their RFI class, whereas 51% of the heifers had a different RFI class in period 2. Furthermore, 41% of the heifers changed their RFI in period 2 by <0.5 SD, whereas the rest of the heifers changed by ≥0.5 SD. These results indicate that reranking exists in heifers despite receiving the same diet in the 2 feeding periods and that the reranking may be more serious in heifers (28%) with extreme RFI performances in each period.     

Heritabilities and genetic correlations for postweaning growth and feed intake of beef bulls and steers

Data from studies conducted at Miles City, MT and Lethbridge, AB were pooled to evaluate genetic and environmental variation in feed intake (MEI), growth rate (ADG), MEI-to-gain ratio (M/G), final weight (FWT), and fat thickness (FAT). A total of 124 sires with an average of 4.25 progeny each were represented in the data. Restricted maximum likelihood methods were used to estimate within and between paternal half-sib estimates of variance and covariance. Heritabilities and genetic, phenotypic, and environmental correlations with inference to populations at 365 d of age were calculated from the estimates. Heritabilities were as follows: ADG, .38 +/- .16; MEI, .45 +/- .17; M/G, .26 +/- .15; FWT .25 +/- .15; and FAT .52 +/- .17. The genetic correlation of MEI with ADG was large (.73 +/- .13) and antagonistic to genetic improvement of M/G through selection for ADG. Efficient genetic improvement in M/G was found to depend on using either MEI or an indicator of composition of gain as selection criteria in addition to ADG. Selection to improve M/G using an index that included FWT and FAT, in addition to MEI and ADG, resulted in greater predicted response in ADG and lesser predicted response in MEI than the index of ADG and MEI alone.     

The effect of residual feed intake classification on forage intake by grazing beef cows

Although feed intake and efficiency differences in growing cattle of low and high residual feed intake (RFI) classification have been established, little is known about the difference in grazed forage intake between beef cows of known RFI classification. Two experiments were conducted using Hereford cows for which RFI had been determined as heifers using the GrowSafe 4000E feed intake system, after which heifers had been divided into thirds as low RFI, mid RFI, and high RFI. During Exp. 1, 2 replicates of low and high RFI cows (n = 7/replicate) in mid- to late-gestation were blocked to 1 of 4 non-endophyte-infected tall fescue paddocks (1.8 to 2.4 ha), which they grazed continuously for 84 d during summer. Using grazing exclosures, weekly rising plate meter readings, and forage harvests every 21 d, average forage DMI was calculated. Low and high RFI groups did not differ (P > 0.05) in BW change or BCS change over the trial (19.5 vs. 22.1 kg of BW gain and 0.11 vs. 0.10 BCS gain), but low RFI cows had a 21% numerically lower DMI than high RFI cows (12.4 vs. 15.6 kg/d; P = 0.23). The average area needed per paddock over the trial was similar for low and high RFI cows (1.71 vs. 1.82 ha; P = 0.35), and the average DM on offer over the trial was less for low RFI than for high RFI cows (4,215 vs. 4,376 kg; P = 0.06). During Exp. 2, 3 replicates of low and high RFI cows with their calves (n = 4 pair/replicate) strip-grazed stockpiled and early spring growth tall fescue paddocks (0.7 to 0.9 ha) for 60 d in late winter and early spring. Because of limiting forage availability and quality at trial initiation, cow-calf pairs were also fed 3.31 kg/pair of pelleted soyhulls daily. Pre- and post-grazed forage samples were harvested for 4 grazing periods, and forage growth was estimated using a growing degree days calculation and on-site weather station data. Performance did not differ (P > 0.05) between low and high RFI cows throughout the experiment (18.4 vs. 26.6 kg of BW gain and -0.04 vs. 0.15 BCS gain). Despite the utilization of forage offered being similar for low and high RFI cow-calf pairs (P > 0.05), low RFI cows and their calves had an 11% numerically lower DMI than high RFI pairs (12.5 vs. 14.1 kg/d; P = 0.12). We concluded that either no intake differences existed between low and high RFI cows or that current methodology and small animal numbers limited our ability to detect differences.     

Simultaneous Bayesian estimation of genetic parameters for curves of weight,feed intake,and residual feed intake in beef cattle

Rates of gain and feed efficiency are important traits in most breeding programs for growing farm animals. The rate of gain (GAIN) is usually expressed over a certain age period and feed efficiency is often expressed as residual feed intake (RFI), defined as observed feed intake (FI) minus expected feed intake based on live weight (WGT) and GAIN. However, the basic traits recorded are always WGT and FI and other traits are derived from these basic records. The aim of this study was to develop a procedure for simultaneous analysis of the basic records and then derive linear traits related to feed efficiency without retorting to any approximation. A bivariate longitudinal random regression model was employed on 13,791 individual longitudinal records of WGT and FI from 2,827 bulls of six different beef breeds tested for their own performance in the period from 7 to 13 mo of age. Genetic and permanent environmental covariance functions for curves of WGT and FI were estimated using Gibbs sampling. Genetic and permanent covariance functions for curves of GAIN were estimated from the first derivative of the function for WGT and finally the covariance functions were extended to curves for RFI, based on the conditional distribution of FI given WGT and GAIN. Furthermore, the covariance functions were extended to include GAIN and RFI defined over different periods of the performance test. These periods included the whole test period as normally used when predicting breeding values for GAIN and RFI for beef bulls. Based on the presented method, breeding values and genetic parameters for derived traits such as GAIN and RFI defined longitudinally or integrated over (parts of) of the test period can be obtained from a joint analysis of the basic records. The resulting covariance functions for WGT, FI, GAIN, and RFI are usually singular but the method presented here does not suffer from the estimation problems associated with defining these traits individually before the genetic analysis. All the results are thus estimated simultaneously, and the set of parameters is consistent.     

Correlated responses in sow appetite, residual feed intake, body composition, and reproduction after divergent selection for residual feed intake in the growing pig

Residual feed intake (RFI) has been explored as an alternative selection criterion to feed conversion ratio to capture the fraction of feed intake not explained by expected production and maintenance requirements. Selection experiments have found that low RFI in the growing pig is genetically correlated with reduced fatness and feed intake. Selection for feed conversion ratio also reduces sow appetite and fatness, which, together with increased prolificacy, has been seen as a hindrance for sow lifetime performance. The aims of our study were to derive equations for sow RFI during lactation (SRFI) and to evaluate the effect of selection for RFI during growth on sow traits during lactation. Data were obtained on 2 divergent lines selected for 7 generations for low and high RFI during growth in purebred Large Whites. The RFI was measured on candidates for selection (1,065 pigs), and sow performance data were available for 480 sows having from 1 to 3 parities (1,071 parities). Traits measured were sow daily feed intake (SDFI); sow BW and body composition before farrowing and at weaning (28.4 ± 1.7d); number of piglets born total, born alive, and surviving at weaning; and litter weight, average piglet BW, and within-litter SD of piglet BW at birth, 21 d of age (when creep feeding was available), and weaning. Sow RFI was defined as the difference between observed SDFI and SDFI predicted for sow maintenance and production. Daily production requirements were quantified by litter size and daily litter BW gain as well as daily changes in sow body reserves. The SRFI represented 24% of the phenotypic variability of SDFI. Heritability estimates for RFI and SRFI were both 0.14. The genetic correlation between RFI and SRFI was 0.29 ± 0.23. Genetic correlations of RFI with sow traits were low to moderate, consistent with responses to selection; selection for low RFI during growth reduced SDFI and increased number of piglets and litter growth, but also increased mobilization of body reserves. No effect on rebreeding performance was found. Metabolic changes previously observed during growth in response to selection might explain part of the better efficiency of the low-RFI sows, decreasing basal metabolism and favoring rapid allocation of resources to lactation. We propose to consider SRFI as an alternative to SDFI to select for efficient sows with reduced input demands during lactation.     

Linkage between the intestinal microbiota and residual feed intake in broiler chickens

Background: Intestinal microbiota plays a key role in nutrient digestion and utilization with a profound impact on feed efficiency of livestock animals. However, the intestinal microbes that are critically involved in feed efficiency remain elusive.Methods: To identify intestinal bacteria associated with residual feed intake(RFI) in chickens, male Cobb broiler chicks were individually housed from day 14 to day 35. Individual RFI values were calculated for 56 chickens.Luminal contents were collected from the ileum, cecum, and cloaca of each animal on day 35. Bacterial DNA was isolated and subjected to 16 S rRNA gene sequencing. Intestinal microbiota was classified to the feature level using Deblur and QIIME 2. High and low RFI groups were formed by selecting 15 and 17 chickens with the most extreme RFI values for subsequent LEfSe comparison of the difference in the microbiota. Spearman correlation analysis was further performed to identify correlations between the intestinal microbiota composition and RFI.Results: No significant difference in evenness, richness, and overall diversity of the microbiota in the ileum, cecum,or cloaca was observed between high and low RFI chickens. However, LEfSe analysis revealed a number of bacterial features being differentially enriched in either high or low RFI chickens. Spearman correlation analysis further identified many differentially enriched bacterial features to be significantly correlated with RFI(P 0.05). Importantly,not all short-chain fatty acid(SCFA) producers showed a positive association with RFI. While two novel members of Oscillibacter and Butyricicoccus were more abundant in low-RFI, high-efficiency chickens, several other SCFA producers such as Subdoligranulum variabile and two related Peptostreptococcaceae members were negatively associated with feed efficiency. Moreover, a few closely-related Lachnospiraceae family members showed a positive correlation with feed efficiency, while others of the same family displayed an opposite relationship.Conclusions: Our results highlight the complexity of the intestinal microbiota and a need to differentiate the bacteria to the species, subspecies, and even strain levels in order to reveal their true association with feed efficiency. Identification of RFI-associated bacteria provides important leads to manipulate the intestinal microbiota for improving production efficiency, profitability, and sustainability of poultry production.     

The relationship between mitochondrial function and residual feed intake in Angus steers

The objective of this study was to examine the relationship between mitochondrial function and residual feed intake in Angus steers. Individual feed intakes were recorded for a contemporary group of 40 steers via the GrowSafe feed intake system. Intakes were then used to calculate residual feed intake (RFI), a measure of efficiency. Based on these calculations, 9 low (RFI = -0.83) and 8 high (RFI = 0.78) RFI animals were selected for further study. Blood samples were collected via jugular venipuncture 1 wk before slaughter for the determination of plasma glucose and insulin concentrations. Tissue samples were taken from the LM from both the high and low RFI animals and mitochondria were isolated for measurement of oxygen consumption and hydrogen peroxide production. Average daily gain and carcass composition were not different between the high and low RFI steers; however, ADFI by the high RFI animals was 1.54 kg/d greater (P < 0.001) than for the low RFI animals. Low RFI steers exhibited a greater (P < 0.05) rate of state 2 and 3 respiration, respiratory control ratio, and hydrogen peroxide production than high RFI steers when provided with glutamate or succinate as a respiratory substrate. The acceptor control and adenosine diphosphate:oxygen ratios were not different between the 2 groups for either substrate. When hydrogen peroxide production was expressed as a ratio to respiration rate there was no difference between groups, signifying that electron leak was similar for both groups. Plasma glucose concentration was greater (P < 0.05) in the high RFI steers than in the low RFI steers; however, plasma insulin concentration was not different (P = 0.22) between the 2 groups. The ratio between plasma glucose and insulin concentration was similar (P = 0.88) between the 2 groups indicating no difference in glucose metabolism. The increased plasma glucose concentration observed in the high RFI steers was presumed to be the result of a greater feed intake by these animals. It seems that mitochondrial function is not different between the high and low RFI groups but rather the rate of mitochondrial respiration is increased in low RFI steers compared with high RFI steers.     

Evaluation of equations to predict body composition in Nellore bulls

The equations developed by Hankins and Howe (1946, HH), Marcondes et al. (2010, M10), Marcondes et al. (in press, M11) and Valadares Filho et al. (2006, V6) were evaluated to predict the body composition from the 9–10–11th rib cut in Nellore bulls. The evaluated equations estimated the physical and the carcass chemical composition, the empty body chemical composition and the noncarcass chemical composition. Thirty-seven Nellore bulls (14±1 months old initially) with shrunk body weight of 259±24.9 kg were used in this experiment. The bulls were randomly divided into three groups: five bulls to the reference group, four bulls were fed at maintenance level and twenty-eight bulls were fed ad libitum. The bulls fed ad libitum were separated into four groups, one of which was slaughtered every 42 days. The diet was composed of corn silage and concentrate (55:45). After slaughter, the 9–10–11th rib cut was dissected into muscle, fat and bone fractions. The remaining carcass was similarly dissected. The others parameters that were evaluated as partial predictors included the empty body weight, the dressing percentage, the visceral fat percentage, the organ and viscera percentage and the composition of the noncarcass components. The values estimated with prediction equations were compared to the observed values. The equations obtained by M11 predicted correctly the carcass physical composition. However, the muscle and fat tissues were under- and overestimated, respectively, by HH. Some constituents of the noncarcass components can be predicted from equations developed by M10. The equations obtained by M10 predicted correctly the carcass and empty body chemical composition. The carcass water was underestimated by HH. The equations by V6 did not predict the carcass or empty body chemical composition. The carcass physical and chemical composition and empty body chemical composition can be predicted from the composition of 9–10–11th rib cut by equations obtained by Marcondes et al., 2010 and MarcondesPlease complete and update the reference given here (preferably with a DOI if the publication data are not known): Marcondes et al. (in press). For references to articles that are to be included in the same (special) issue, please add the words ‘this issue’ wherever this occurs in the list and, if appropriate, in the text. et al., while the composition of these components cannot be predicted by Hankins and Howe (1946) and Valadares Filho et al. (2006) in Nellore bulls.     

Selection response and genetic parameters for residual feed intake in Yorkshire swine

Residual feed intake (RFI) is a measure of feed efficiency defined as the difference between the observed feed intake and that predicted from the average requirements for growth and maintenance. The objective of this study was to evaluate the response in a selection experiment consisting of a line selected for low RFI and a random control line and to estimate the genetic parameters for RFI and related production and carcass traits. Beginning with random allocation of purebred Yorkshire littermates, in each generation, electronically measured ADFI, ADG, and ultrasound backfat (BF) were evaluated during a approximately 40- to approximately 115-kg of BW test period on approximately 90 boars from first parity and approximately 90 gilts from second parity sows of the low RFI line. After evaluation of first parity boars, approximately 12 boars and approximately 70 gilts from the low RFI line were selected to produce approximately 50 litters for the next generation. Approximately 30 control line litters were produced by random selection and mating. Selection was on EBV for RFI from an animal model analysis of ADFI, with on-test group and sex (fixed), pen within group and litter (random), and covariates for interactions of on- and off-test BW, on-test age, ADG, and BF with generations. The RFI explained 34% of phenotypic variation in ADFI. After 4 generations of selection, estimates of heritability for RFI, ADFI, ADG, feed efficiency (FE, which is the reciprocal of the feed conversion ratio and equals ADG/ ADFI), and ultrasound-predicted BF, LM area (LMA), and intramuscular fat (IMF) were 0.29, 0.51, 0.42, 0.17, 0.68, 0.57, and 0.28, respectively; predicted responses based on average EBV in the low RFI line were -114, -202, and -39 g/d for RFI (= 0.9 phenotypic SD), ADFI (0.9 SD), and ADG (0.4 SD), respectively, and 1.56% for FE (0.5 SD), -0.37 mm for BF (0.1 SD), 0.35 cm(2) for LMA (0.1 SD), and -0.10% for IMF (0.3 SD). Direct phenotypic comparison of the low RFI and control lines based on 92 low RFI and 76 control gilts from the second parity of generation 4 showed that selection had significantly decreased RFI by 96 g/d (P = 0.002) and ADFI by 165 g/d (P < 0.0001). The low RFI line also had 33 g/d lower ADG (P = 0.022), 1.36% greater FE (P = 0.09), and 1.99 mm less BF (P = 0.013). There was not a significant difference in LMA and other carcass traits, including subjective marbling score, despite a large observed difference in ultrasound-predicted IMF (-1.05% with P < 0.0001). In conclusion, RFI is a heritable trait, and selection for low RFI has significantly decreased the feed required for a given rate of growth and backfat.