Identification of biomarkers associated with the feed efficiency by metabolomics profiling:results from the broiler lines divergent for high or low abdominal fat content

Background:Improving feed efficiency(FE)is one of the main objectives in broiler breeding.It is difficult to directly measure FE traits,and breeders hence have been trying to identify biomarkers for the indirect selection and improvement of FE traits.Metabolome is the"bridge"between genome and phenome.The metabolites may potentially account for more of the phenotypic variation and can suitably serve as biomarkers for selecting FE traits.This study aimed to identify plasma metabolite markers for selecting high-FE broilers.A total of 441 birds from Northeast Agricultural University broiler lines divergently selected for abdominal fat content were used to analyze plasma metabolome and estimate the genetic parameters of differentially expressed metabolites.Results:The results identified 124 differentially expressed plasma metabolites(P<0.05)between the lean line(highFE birds)and the fat line(low-FE birds).Among these differentially expressed plasma metabolites,44 were found to have higher positive or negative genetic correlations with FE traits(|r_g|≥0.30).Of these 44 metabolites,14 were found to display moderate to high heritability estimates(h~2≥0.20).However,among the 14 metabolites,4 metabolites whose physiological functions have not been reported were excluded.Ultimately,10 metabolites were suggested to serve as the potential biomarkers for breeding the high-FE broilers.Based on the physiological functions of these metabolites,reducing inflammatory and improving immunity were proposed to improve FE and increase production efficiency.Conclusions:According to the pipeline for the selection of the metabolite markers established in this study,it was suggested that 10 metabolites including 7-ketocholesterol,dimethyl sulfone,epsilon-(gamma-glutamyl)-lysine,gamma-glutamyltyrosine,2-oxoadipic acid,L-homoarginine,testosterone,adenosine 5'-monophosphate,adrenic acid,and calcitriol could be used as the potential biomarkers for breeding the"food-saving broilers".

Agolin Ruminant®, an Essential Oil Blend, Increases Energy-Corrected Milk and Feed Efficiency in a High Component Dairy Herd

Agolin® Ruminant (Agolin) is a blend of essential oils developed to improve feed efficiency while at the same time reducing rumen enteric methane production. Studies have shown that the product improves lactational performance, but the range of results has been varied. This experiment evaluated the effects of the feed additive Agolinon milk production in a high-component (fat and protein) dairy herd when provided for an extended time. The experiment was conducted at a large commercial dairy in the Pacific Northwest, USA. Eight pens of cows (350 to 500 cows/pen) were blocked by production, and pens within blocks were randomly assigned to treatment. All pens received a common total mixed ration. Treatment consisted of providing 1 g/cow/day of Agolin to the test group. A 4-week adaptation period was followed by an 11-week study period. Milk production and milk composition were determined by cow by averaging daily performance for the one-week period before the start of the trial (covariate period) and the last week of each of the two test periods. Feed intakes were determined by pen at the same time. Milk yield was 1.11 kg/cow/day greater (P < 0.001) at the midpoint and 1.48 kg/cow/day greater (P < 0.001) at the end of the test period for cows receiving the feed additive. Similarly, protein yields were 0.03 (P < 0.001) and 0.07 kg/cow/day greater (P < 0.001) at the midpoint and end of the feeding period. Milk fat yield was not different (P = 0.854) between treatment groups at the midpoint of the trial but increased with treatment (P = 0.002) by the end of the trial. Energy-corrected milk/feed ratio, based on pen parameters, was significantly altered by treatment at the final test period (1.48 vs. 1.64 kg/kg for control and test treatments, respectively).

A review of feed efficiency in swine:biology and application

Feed efficiency represents the cumulative efficiency with which the pig utilizes dietary nutrients for maintenance, lean gain and lipid accretion. It is closely linked with energy metabolism, as the oxidation of carbon-containing components in the feed drive all metabolic processes. While much is known about nutrient utilization and tissue metabolism, blending these subjects into a discussion on feed efficiency has proven to be difficult. For example, while increasing dietary energy concentration will almost certainly increase feed efficiency, the correlation between dietary energy concentration and feed efficiency is surprisingly low. This is likely due to the plethora of non-dietary factors that impact feed efficiency, such as the environment and health as well as individual variation in maintenance requirements, body composition and body weight. Nonetheless, a deeper understanding of feed efficiency is critical at many levels. To individual farms, it impacts profitability. To the pork industry, it represents its competitive position against other protein sources. To food economists, it means less demand on global feed resources. There are environmental and other societal implications as well. Interestingly, feed efficiency is not always reported simply as a ratio of body weight gain to feed consumed. This review will explain why this arithmetic calculation, as simple as it initially seems, and as universally applied as it is in science and commerce, can often be misleading due to errors inherent in recording of both weight gain and feed intake. This review discusses the importance of feed efficiency, the manner in which it can be measured and reported, its basis in biology and approaches to its improvement. It concludes with a summary of findings and recommendations for future efforts.

New insights into the associations among feed efficiency, metabolizable efficiency traits and related QTL regions in broiler chickens

Background: Improving the feed efficiency would increase profitability for producers while also reducing the environmental footprint of livestock production. This study was conducted to investigate the relationships among feed efficiency traits and metabolizable efficiency traits in 180 male broilers. Significant loci and genes affecting the metabolizable efficiency traits were explored with an imputation-based genome-wide association study. The traits measured or calculated comprised three growth traits, five feed efficiency related traits, and nine metabolizable efficiency traits.Results: The residual feed intake(RFI) showed moderate to high and positive phenotypic correlations with eight other traits measured, including average daily feed intake(ADFI), dry excreta weight(DEW), gross energy excretion(GEE), crude protein excretion(CPE), metabolizable dry matter(MDM), nitrogen corrected apparent metabolizable energy(AMEn), abdominal fat weight(Ab F), and percentage of abdominal fat(Ab P). Greater correlations were observed between growth traits and the feed conversion ratio(FCR) than RFI. In addition, the RFI, FCR, ADFI, DEW,GEE, CPE, MDM, AMEn, Ab F, and Ab P were lower in low-RFI birds than high-RFI birds(P < 0.01 or P < 0.05), whereas the coefficients of MDM and MCP of low-RFI birds were greater than those of high-RFI birds(P < 0.01). Five narrow QTLs for metabolizable efficiency traits were detected, including one 82.46-kb region for DEW and GEE on Gallus gallus chromosome(GGA) 26, one 120.13-kb region for MDM and AMEn on GGA1, one 691.25-kb region for the coefficients of MDM and AMEn on GGA5, one region for the coefficients of MDM and MCP on GGA2(103.45–103.53 Mb), and one 690.50-kb region for the coefficient of MCP on GGA14. Linkage disequilibrium(LD) analysis indicated that the five regions contained high LD blocks, as well as the genes chromosome 26 C6 orf106 homolog(C26 H6 orf106), LOC396098, SH3 and multiple ankyrin repeat domains 2(SHANK2), ETS homologous factor(EHF), and histamine receptor H3-like(HRH3 L), which are known to be involved in the regulation of neurodevelopment, cell proliferation and differentiation, and food intake.Conclusions: Selection for low RFI significantly decreased chicken feed intake, excreta output, and abdominal fat deposition, and increased nutrient digestibility without changing the weight gain. Five novel QTL regions involved in the control of metabolizable efficiency in chickens were identified. These results, combined through nutritional and genetic approaches, should facilitate novel insights into improving feed efficiency in poultry and other species.

Systematic analysis of feeding behaviors and their effects on feed efficiency in Pekin ducks

Background： Feeding behavior study is important for animal husbandry and production. However, few studies were conducted on the feeding behavior and their relationship with feeding efficiency in Pekin ducks. In order to investigate the feeding behavior and their relationship with feed efficiency and other economic traits in Pekin ducks, we selected 358 male Pekin ducks and recorded feeding information between 3 to 6 wk of age using automatic electronic feeders, and compared the feeding behavior under different residual feed intake（RFI） levels.Results： We observed that total feed time, daily feed intake and feed intake per meal had strong positive correlations with feed efficiency traits; moreover, strong correlation between feed intake per meal and body weight was found（R=0.32, 0.36）. Daily feeding rate meal and meal duration had weak correlations with feed efficiency（R=0.14~0.15）. The phenotypic correlation of between-meal pauses, with feed efficiency was not observed. When daily changes were analyzed, high RFI ducks had the highest feed consumption over all times, and obvious differences in daily visits were found among different RFI level animals during the middle period; these differences were magnified with age, but there was no difference in daily meal number. Moreover, our data indicate that high RFI birds mainly take their meals at the edge of the population enclosure, where they are more susceptible to environmental interference.Conclusions： Overal, this study suggests that the general feeding behaviors can be accurately measured using automatic electronic feeders and certain feeding behaviors in Pekin ducks are associated with improved feed efficiency.

Identification of gut microbes associated with feed efficiency by daily-phase feeding strategy in growing-finishing pigs

Feed efficiency is one of the most important issues for sustainable pig production.Daily-phase feeding(DPF)is a form of precision feeding that could improve feed efficiency in pigs.Gut microbiota can regulate host nutrient digestion,absorption,and metabolism.However,which key microbes may play a vital role in improving the feed efficiency during DPF remains unclear.In the present study,we used a DPF program compared to a three-phase feeding(TPF)program in growing-finishing pigs to investigate the effects of gut microbiota on feed efficiency.A total of 204 Landrace×Yorkshire pigs(75 d)were randomly assigned into 2 treatments.Each treatment was replicated 8 times with 13 to 15 pigs per replicate pen.Pigs in the TPF group were fed with a commercial feeding program that supplied fixed feed for phasesⅠ,Ⅱ,andⅢ,starting at 81,101,and 132 d of age,respectively,and pigs in the DPF group were fed a blend of adjacent phase feed from 81 to 155 d at a gradual daily ratio and phaseⅢfeed from 155 to 180 d of age.Daily feed intake and body weight were recorded by a computerized device in the feeders.Feces and blood samples were collected from 1 pig per replicate at 155 and 180 d of age.The results showed that the DPF program remarkably improved the feed efficiency at 155 d(P<0.001)and 180 d of age(P<0.001),with a significant reduction of the intake of crude protein(P<0.01),net energy(P<0.001),crude fiber(P<0.001),ether extract(P<0.01),and ash(P<0.001).The daily-phase feeding program increased the abundance of Prevotella copri(P<0.05)and Paraprevotella clara(P<0.05),while it decreased the abundance of Ocilibacter(P<0.05)at 155 d of age.The results of correlation analysis indicated that the differentially abundant microbiota communities were closely associated with 20 metabolites which enriched amino acid and phenylalanine metabolism.Our results suggest that 2 key microbes may contribute to feed efficiency during daily-phase feeding strategies in pigs.

Effect of Two Substrate Types on Feeding Efficiency by Juvenile Chinese Sturgeon Acipenser sinensis on Barcheek Goby Rhinogobius giurinus

We conducted experiments in an artificial stream tank with wild juvenile Chinese sturgeon Acipenser sinensis captured in the Yangtze Estuary to test the null hypothesis that their feeding efficiency on Barcheek goby Rhinogobius giurinus was not affected by sand vs. smooth glass substrate. Gobies are among the most common prey eaten by wild juvenile A. sinensis in the estuary. Test results found neither substrate type significantly affected feeding efficiency by juveniles. Previous research found a strong innate habitat preference of A. sinensis for sand substrate. The present results indicate that the preference for sand is not related to efficiently capturing R. giurinus on sand, but is an adaptation predisposing juvenile A. sinensis to seek sandy substrate where R. giurinus and other benthic forage are the most abundant in the Yangtze Estuary.

Understanding the role of rumen epithelial host-microbe interactions in cattle feed efficiency

Feed efficiency is one of the economically important traits for the cattle industry that affects profit(feed costs)and the environment(production of manure and methane).Due to that feed efficiency is driven by multi-factors,mechanisms contributing to the animal to animal variation in this trait have not been well defined,limiting the development of precision feeding strategies to improve the herd production efficiency.Rumen microbial fermentation and volatile fatty acids(VFA)production have been recently reported to be associated with cattle feed efficiency,however the roles of rumen epithelial function in feed efficiency are less studied although the rumen epithelium has an important function in VFA absorption and metabolism which can affect host feed efficiency.Rumen epithelium is colonized with a diverse microbial population,termed epimural microbiota,which has proposed functions in tissue development,barrier and inflammation,urea transport,and oxygen scavenging,suggesting that they can affect rumen epithelial functions and subsequently cattle feed efficiency.Especially,prospective functions of epimural microbiota,enhanced rumen immunity and increased rumen epithelial thickness,might contribute to less nutritional requirement for tissue recuperation.Thus,the understanding of the functions of rumen epithelium,epimural microbiota,and rumen epithelial host-microbe interactions is essential to identify their roles in contributing to feed efficiency.In this review,we will focus on to date research findings on the structure of rumen epithelium,epimural microbiota,and epithelial host-microbe interactions together with their functions and how these are associated with feed efficiency,aiming to provide insights on future directions to study rumen epithelial host-microbe interactions and improve the rumen functions in cattle.

Dietary lecithin improves feed efficiency without impacting meat quality in immunocastrated male pigs and gilts fed a summer ration containing added fat

The aim of this study was to investigate the effects of sex and dietary lecithin on growth performance,meat quality, muscle collagen content and gene expression of key genes involved in collagen synthesis in finisher pigs.A total of 256 pigs(Large White × Landrace) were allotted to a 2 × 2 factorial arrangement involving sex(gilt or immunocastrated [IC] male) and dietary treatment(0 or 5 g/kg of dietary lecithin).All diets were formulated to contain 4.6% tallow with relatively high total fat of 6.3%.After 5 weeks of dietary treatment, pigs were slaughtered and Longissimus dorsi muscle was obtained for evaluation of meat quality and collagen content.Rectus abdominis muscle was analysed for gene expression of key genes involved in collagen synthesis namely, type Ⅰ(a1) procollagen(COL1A1), type Ⅲ(a1) procollagen(COL3A1), a-subunit of prolyl 4-hydroxylase(P4H), lysyl oxidase and metalloproteinase-1(MMP-1).The results showed that lecithin improved feed efficiency of all pigs(P < 0.05) but it had no effect on feed intake, average daily gain and dressing percentage(P > 0.05).Lecithin also had no effect on meat compression, shear force, collagen content and gene expression(P > 0.05).Immunocastrated male had higher growth rate and increased COL1 A1 expression than gilts.However, sex had no effect on fat depth at the P2 site(65 mm from the midline over the last rib), collagen content and expression of other genes(P > 0.05).In conclusion, lecithin improved feed efficiency in finishing pigs without impacting pork quality.Thus, inclusion of lecithin in diets containing high amount of tallow during the summer period could be beneficial.

A Method of Drawing Upseleciton Index for Improving Feed Efficiency

Based on the beneficial trait which is from the two component traits of feed efficiency by price, a method for drawing up selection index to improve feed efficiency is discussed. The method avoids some troubles from directly selecting feed efficiency and settles the questions to draw up selection index for the kind of ratio traits simultaneously.

Functional Genes in Relation to Residual Feed Intake in Murrah Buffalo Heifers

High Feed efficiency (FE) in growing heifers has economic importance in dairy, but remains less understood in buffaloes. Feed conversion efficiency is defined as dry matter intake (DMI) per unit body weight gain and is determined as residual feed intake (RFI), i.e., the difference between actual and predicted feed intake to gain unit body weight during a feed trial run for 78 days under control feeding. A large variation was identified ranging between -0.42 to 0.35 in growing buffalo heifers (n = 40) of age between 11 to 15 months. An average daily weight gain (ADG) varied between 382.0 and 807.6 g/day when compared with the control-fed heifers at an organized buffalo farm. The whole blood transcriptome data obtained from the selected growing heifers from extremes of estimated high and low RFI efficiency were compared with the reference assembly generated from the transcriptome of multiparous buffaloes (n = 16) of diverse age of maturity, period of regaining post partum cyclicity and level of milk production. Differentially expressed genes (DEGs) were identified using the reference genome of Mediterranean water buffalo. GO: terms (Padj 0.05, FDR 0.05) enriched by annotated DEGs and biological pathways in gene network for RFI efficiency trait were identified. GO: terms specific to pre-transcriptional regulation of nucleus and Chromatin organization under Nucleoplasm, Energy balancing, Immunity, Cell signaling, ROS optimization, ATP generation through the Electron Transport chain and cell proliferation were determined. The study reveals the indicators targeting the actual metabolic changes and molecular functions underlying the feed utilization capacity of buffaloes. Estimated RFI efficiency revealed a large variation over heifers which may lower the DMI even up to 13.6% thus, enabling an increase in ADG up to 16% by involving efficient heifers in breeding plan. The study revealed a scope of high gain by selective breeding for FE in heifers. FE variants catalogued in the study are useful breed-specific RFI markers for future reference. The study contributes to the understanding of feed efficiency in buffaloes and its association with key interactive traits such as reproduction and growth. This knowledge can be utilized to develop more effective breeding programs.

Residual feed intake divergence during the preweaning period is associated with unique hindgut microbiome and metabolome profiles in neonatal Holstein heifer calves

Background:Recent studies underscored that divergence in residual feed intake(RFI)in mature beef and dairy cattle is associated with changes in ruminal microbiome and metabolome profiles which may contribute,at least in part,to better feed efficiency.Because the rumen in neonatal calves during the preweaning period is underdeveloped until close to weaning,they rely on hindgut microbial fermentation to breakdown undigested diet components.This leads to production of key metabolites such as volatile fatty acids(VFA),amino acids,and vitamins that could potentially be absorbed in the hind-gut and help drive growth and development.Whether RFI divergence in neonatal calves is associated with changes in hindgut microbial communities and metabolites is largely unknown.Therefore,the objective of the current study was to determine differences in hindgut microbiome and metabolome in neonatal Holstein heifer calves retrospectively-grouped based on feed efficiency as mostefficient(M-eff)or least-efficient(L-eff)calves using RFI divergence during the preweaning period.Methods:Twenty-six Holstein heifer calves received 3.8 L of first-milking colostrum from their respective dams within 6 h after birth.Calves were housed in individual outdoor hutches bedded with straw,fed twice daily with a milk replacer,and had ad libitum access to a starter grain mix from birth to weaning at 42 d of age.Calves were classified into M-eff[n=13;RFI coefficient=−5.72±0.94 kg DMI(milk replacer+starter grain)/d]and L-eff[n=13;RFI coefficient=5.61±0.94 kg DMI(milk replacer+starter grain)/d]based on a linear regression model including the combined starter grain mix and milk replacer DMI,average daily gain(ADG),and metabolic body weight(MBW).A deep sterile rectal swab exposed only to the rectum was collected immediately at birth before colostrum feeding(i.e.,d 0),and fecal samples at d 14,28,and 42(prior to weaning)for microbiome and untargeted metabolome analyses using 16S rRNA gene sequencing and LC-MS.Microbiome data were analyzed with the QIIME 2 platform and metabolome data with the MetaboAnalyst 4.0 pipeline.Results:No differences(P>0.05)in body measurements including body weight(BW),body length(BL),hip height(HH),hip width(HW),and wither height(WH)were detected between M-eff and L-eff calves at birth and during preweaning.Although milk replacer intake did not differ between groups,compared with L-eff,M-eff heifers had lower starter intake(P<0.01)between d 18 to 42 of age,whereas no differences(P>0.05)for ADG,cumulative BWG,or body measurements were observed between RFI groups during the preweaning period.Microbiome and metabolome profiles through the first 42 d of age indicated greater hindgut capacity for the production of energy-generating substrates(butyrate and propionate)and essential nutrients(vitamins and amino acids)in heifers with greater estimated feed efficiency.Conclusion:Despite consuming approximately 54.6%less solid feed(cumulative intake,10.90 vs.19.98±1.66 kg)from birth to weaning,the microbiome-metabolome changes in the hindgut of most-efficient heifers might have helped them maintain the same level of growth as the least-efficient heifers.

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 16S 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.

Body composition and compensatory growth in Nile tilapia Oreochromis niloticus under different feeding intervals

We investigated the growth and body composition of Nile tilapia under five different feeding regimes. A control group was fed to satiation twice daily for 185 days; four treatment groups were fed at intervals of 2, 3, 4 or 7 days(dietary ‘restricted' period, days 0–80) and then fed to satiation(‘refeeding' period, days 80–185). Compensatory growth in weight and length of the feed-restricted groups was observed during the refeeding period. However, the growth of none of the restricted groups caught up with that of the control group over the experimental period. Feed intake upon refeeding increased with the duration of deprivation. There were no significant differences in feed efficiency between the restricted and control groups during the refeeding stage, suggesting that hyperphagia was the mechanism responsible for the increased growth rates during this period. Tilapia preferentially used n-3 polyunsaturated fatty acids and nonessential amino acids during the restricted-feeding period. Higher production was achieved by higher feed consumption. We suggest that if attainment of market size in minimum time is required, fish should be consistently fed to satiation, while taking care to avoid the possible negative consequences of overfeeding.

Evaluation of Agolin^®, an Essential Oil Blend, as a Feed Additive for High Producing Cows

There is a growing demand for feed additives that can not only reduce dairy enteric methane emissions but also increase milk production and feed efficiency. Just one product is currently commercially available which accomplishes both of these goals. The purpose of this study was to confirm the performance benefits of the product (Agolin?, Agolin SA, Biere, Switzerland) in high producing mid-lactation dairy cows under United States feeding conditions. Four matched pens of approximately 150 mid-lactation cows/pen and averaging over 50 kg of milk/cow/day were enrolled in a side-by-side study. All pens received a common total mixed diet ad libitum, and the essential oil blend was administered via a concentrated farm pack to provide 1 g/cow/day to cows in the 2 test pens. Milk weights were determined, and samples were collected for compositional analysis over the last 2 days of the pretrial (May 11 and 12, 2020) and end of the trial (July 18 and 19, 2020) periods. Dry matter intake was measured by pen daily for the last 10 days of each feeding period. Milk fat and milk protein yields were greater (P < 0.05) for cows receiving added Agolin. There was a tendency (P = 0.06) for energy corrected milk/dry matter intake to be greater for cows receiving the Agolin (1.88) relative to the control diet (1.76). The trial showed that Agolin assisted in improving production parameters of economic importance to dairy producers.

Stress and immunological response of heifers divergently ranked for residual feed intake following an adrenocorticotropic hormone challenge

Background： When an animal is exposed to a stressor, metabolic rate, energy consumption and utilisation increase primarily through activation of the hypothalamic-pituitary-adrenal（HPA） axis. Changes to partitioning of energy by an animal are likely to influence the efficiency with which it is utilised. Therefore, this study aimed to determine the physiological stress response to an exogenous adrenocorticotropic hormone（ACTH） challenge in beef heifers divergently ranked on phenotypic residual feed intake（RFI）.Results： Data were collected on 34 Simmental weaning beef heifers the progeny of a well characterized and divergently bred RFI suckler beef herd. Residual feed intake was determined on each animal during the postweaning stage over a 91-day feed intake measurement period during which they were individually offered adlibitum grass silage and 2 kg of concentrate per head once daily. The 12 highest [0.34 kg DM/d] and 12 lowest[-0.48 kg DM/d] ranking animals on RFI were selected for use in this study. For the physiological stress challenge heifers（mean age 605 ± 13 d; mean BW 518 ± 31.4 kg） were fitted aseptically with indwelling jugular catheters to facilitate intensive blood collection. The response of the adrenal cortex to a standardised dose of ACTH（1.98 IU/kg metabolic BW^（0.75）） was examined. Serial blood samples were analysed for plasma cortisol, ACTH and haematology variables. Heifers differing in RFI did not differ（P = 0.59） in ACTH concentrations. Concentration of ACTH peaked（P 〈 0.001） in both RFI groups at 20 min post-ACTH administration, following which concentration declined to baseline levels by 150 min. Similarly, cortisol systemic profile peaked at 60 min and concentrations remained continuously elevated for 150 min. A RFI × time interaction was detected for cortisol concentrations（P = 0.06） with high RFI heifers had a greater cortisol response than Low RFI from 40 min to 150 min relative to ACTH administration. Cortisol response was positively associated with RFI status（r = 0.32; P 〈 0.01）. No effect of RFI was evident for neutrophil, lymphocytes, monocyte, eosinophils and basophil count. Plasma red blood cell number（6.07 vs. 6.23; P = 0.02） and hematocrit percentage（23.2 vs. 24.5; P = 0.02） were greater for low than high RFI animals.Conclusions： Evidence is provided that feed efficiency is associated with HPA axis function and susceptibility to stress, and responsiveness of the HPA axis is likely to contribute to appreciable variation in the efficiency feed utilisation of cattle.

Residual Feed Intake as a Measure to Select Genetically Productive Beef Cattle: A Review

Measures such as residual feed intake(RFI)have been increasingly considered to select cattle with superior feed efficiency,as it is a characteristic of feed efficiency calculated as the difference between observed intake and estimated intake considering metabolic weight and the weight gain.Estimated feed intake is obtained through the multiple regression equation of observed consumption on metabolic mean live weight and weight gain.The standard was shared among animals into one herd selected for low RFI(high efficiency)and compared to the one selected for high RFI(low efficiency).There was no correlated response in weight per year and in weight gain,and the effectiveness of low RFI selection in reducing feed costs was proven without affecting production.However,selection of animals with negative RFI is not done by selecting animals directly according to the size of the viscera,rather it is done indirectly,that is,when selecting the most efficient animals and normally these animals already have the smallest viscera size.The RFI is a trait that presents genetic variability,selectable to improve and has moderate heritability,between 0.30 and 0.35.The RFI is important because it reduces the direct economic impacts of reduced feed intake,as well as the effects of environmental impact on reducing methane emissions from enteric fermentation of ruminants.

Evaluation of Agolin® Ruminant, an Essential Oil Blend, as a Feed Additive for Cows at Two Levels of Production

Agolin® Ruminant (Agolin) is a commercially available blend of essential oils which has been demonstrated to reduce greenhouse gas emissions in dairy cows and improve energy corrected milk and feed efficiency. Further trials are needed with large numbers of cows to confirm the magnitude of effect of this feed additive on milk production under differing feeding conditions and stages of lactation. Information that can be quantified from newer on-farm systems of measurement is likewise needed. This study was conducted to determine the effects of this additive on high producing (48 kg of milk/day average) just past peak lactation and medium producing dairy cows (43 kg of milk/day average) further along in lactation under commercial conditions that would typically occur in the Pacific Northwest USA. Four pens of approximately 400 Holstein cows/pen (two high producing pens and two medium producing pens) were available for this side-by side study. Performance results were determined using data derived from a subscription standardized monitoring system (High Desert Dairy Laboratory, Inc, Nampa, ID, USA) that provided results for milk yield, fat percentage and protein percentage. As well daily in-stall electronic monitoring of milk only was available. All pens received a common total mixed ration typical of rations fed in the Pacific Northwest, USA. The Agolin feed additive was dispensed through the bulk mineral supply with control cows receiving the normal minerals and the treatment cows receiving the normal minerals plus Agolin. The trial began on August 24, 2021, with treatment cows provided with 1 g/head/day for the duration of the 8-week long study. Dry matter intakes were determined daily for the week before the trial was conducted and the last week of the trial. Treatment results were compared using a general linear model that considered pretrial milk, fat yield and protein yield, days in milk and lactation number. There were 678 high producing cows available for the duration of the study. Based on the standardized testing results, milk yield was greater (1.12 kg/cow/day;P < 0.05) for the cows in the treatment group. There was a tendency for fat corrected milk (FCM) and energy corrected milk (ECM) to be greater for the cows receiving the Agolin feed additive (0.96 and 0.86 kg/cow/day for FCM and ECM respectively, P < 0.10). There were 646 medium producing cows that participated in the trial. There was no treatment effect upon milk production (P = 0.27). There was a significant (P < 0.05) increase in milk fat yield and no change (P = 0.33) in protein yield for the treatment cows in this test group, resulting in greater FCM and ECM (1.12 and 0.95 kg/cow/day;P < 0.05). Daily milk monitoring resulted in a reduced decline in milk yield from the week before to the final week of the trial revealing greater persistency of milk for Agolin-fed cows in both high and medium production pens (1.58 and 2.13 kg/cow/day;P < 0.01). Likewise, overall feed efficiency was improved by 5.3% (P < 0.05) with the test product.

Influence of the Feed Gas Composition on the Fischer-Tropsch Synthesis in Commercial Operations

Key technical challenges relating to the Fischer-Tropsch （F-T） synthesis applied in the commercialization of coal/gas-to-liquids （CTL/GTL） technologies have been reviewed. Based on the experiences accumulated from pilot plant, semi-work test and lab researches, the influences of the H2/CO ratio and the CO2 in the feed gas on the F-T process as well as on CTL/GTL complex in terms of product yields, energy efficiency and carbon utilization efficiency have been studied. Being contrary to the current design schemes for F-T process using the coal derived syngas and the iron-based cata lyst, it is suggested to feed the F-T synthesis unit with a syngas having a H2/CO ratio of 0.5 and then adjusting to 1.4 via the recycling process. As a result, the carbon efficiency of the whole plant could be reached to as high as 50%. For the issue of CO2 addition to the feed gas, it is proved that only a diluting role is played under the current commercial slurry phase F-T process.

Integrated multi-omics reveals the relationship between growth performance,rumen microbes and metabolic status of Hu sheep with different residual feed intakes

Residual feed intake(RFI)is a metric that provides a more accurate measure of feed efficiency.The lower the RFI,the higher the feed efficiency.The changes in the host microbiome and metabolome contribute to the greater feed efficiency of low RFI(LRFI)animals.The aim of this study was to explore the differences in rumen microorganisms,rumen metabolites and plasma metabolites of Hu sheep with differing RFI through the microbiome and metabolome.A total of 80 Hu sheep were used.The experiment consisted of a 15-d pretrial period and a 128-d experimental period.The RFI in the experimental period was calculated for all sheep,and the sheep were screened into high RFI(HRFI,n=8)and LRFI(n=8)groups.The HRFI and LRFI sheep did not differ in their initial and final body weights,average daily gain and body measurements,but the dry matter intake of LRFI sheep was significantly decreased(28.4%,P<0.001).The sheep with LRFI had higher digestibility of crude protein(P=0.010)and ether extract(P=0.010)compared to HRFI group.The concentrations of acetate(P=0.036),propionate(P=0.010),valerate(P=0.027)and total volatile fatty acids(P=0.048)in rumen of LRFI group were higher compared to HRFI group.The results of 16S rDNA sequencing indicated that the sheep with LRFI had higher proportions of Prevotella genus in rumen liquid(P=0.031).The rumen metabolome and plasma metabolome results showed that the citrate cycle,pyruvate metabolism and alanine,aspartate and glutamate metabolism processes were more active for sheep in LRFI group,which provided more energy substrate such as malic acid,oxoglutaric acid and citric acid.In conclusion,sheep with LRFI can utilize feed more efficiently,and the more active energy metabolism pathway and the production of energy substances may account for the higher feed efficiency.