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.

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.

Quantitative analysis of ruminal methanogenic microbial populations in beef cattle divergent in phenotypic residual feed intake(RFI)offered contrasting diets

Background：Methane（CH_4） emissions in cattle are an undesirable end product of rumen methanogenic fermentative activity as they are associated not only with negative environmental impacts but also with reduced host feed efficiency.The aim of this study was to quantify total and specific rumen microbial methanogenic populations in beef cattle divergently selected for residual feed intake（RFI） while offered（i） a low energy high forage（HF） diet followed by（ii） a high energy low forage（LF） diet.Ruminal fluid was collected from 14 high（H）and 14 low（L） RFI animals across both dietary periods.Quantitative real time PCR（qRT-PCR） analysis was conducted to quantify the abundance of total and specific rumen methanogenic microbes.Spearman correlation analysis was used to investigate the association between the relative abundance of methanogens and animal performance,rumen fermentation variables and diet digestibility.Results：Abundance of methanogens,did not differ between RFI phenotypes.However,relative abundance of total and specific methanogen species was affected（P〈 0.05） by diet type,with greater abundance observed while animals were offered the LF compared to the HF diet.Conclusions：These findings suggest that differences in abundance of specific rumen methanogen species may not contribute to variation in CH_4 emissions between efficient and inefficient animals,however dietary manipulation can influence the abundance of total and specific methanogen species.

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.

Alterations in nutrient digestion and utilization associated with different residual feed intake in Hu sheep

Improving feed efficiency is crucial to the animal industry.Residual feed intake(RFI)is now regarded as an index of feed efficiency evaluation and is independent of growth characteristics.Our study aims to explore the alterations in growth performance and nutrient digestion in Hu sheep with different RFI phenotypes.Sixty-four male Hu sheep(body weight=24.39±1.12 kg;postnatal days=90±7.9)were selected for the study.After an evaluation period of 56 days and power analysis,samples were collected from 14 low RFI(L-RFI group,power=0.95)and 14 high RFI sheep(H-RFI group,power=0.95).The L-RFI sheep yielded a lower(P<0.05)feed conversion ratio and dry matter intake;however,both groups exhibited similar average daily gain(P>0.05).The acid detergent fiber,neutral detergent fiber,organic matter,and crude protein apparent digestibility were higher(P<0.05)in L-RFI sheep.N intake and fecal N output(%of N intake)were lower(P<0.05)and N retention(%of N intake)was higher(P<0.05)in L-RFI sheep,whereas no difference(P>0.05)was found in urine N output(%of N intake)between the 2 groups.Furthermore,L-RFI sheep gave lower(P<0.05)serum glucose concentrations and higher(P<0.05)non-esterified fatty acid concentrations.Meanwhile,a lower ruminal acetate molar proportion(P<0.05)and higher propionate molar proportion(P<0.05)were observed in L-RFI sheep.In summary,these results revealed that despite having lower dry matter intake,L-RFI sheep possess higher nutrient digestibility,N retention,ruminal propionate production and serum glucose utilization,in order to meet energy demands.Selection for low RFI sheep could reduce feed costs,which in turn provides economic benefits to the sheep industry.

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.

Circulating leptin and its muscle gene expression in Nellore cattle with divergent feed efficiency

Background： Leptin has a strong relation to important traits in animal production, such as carcass composition,feed intake, and reproduction. It is mainly produced by adipose cells and acts predominantly in the hypothalamus.In this study, circulating leptin and its gene expression in muscle were evaluated in two groups of young Nellore bulls with divergent feed efficiency. Individual dry matter intake（DMI） and average daily gain（ADG） of 98 Nellore bulls were evaluated in feedlot for 70 d to determinate the residual feed intake（RFI） and select 20 animals for the high feed efficient（LRFI） and 20 for the low feed efficient（HRFI） groups. Blood samples were collected on d 56 and at slaughter（80 d） to determine circulating plasma leptin. Samples of Longissimus dorsi were taken at slaughter for leptin gene expression levels.Results： DMI and RFI were different between groups and LRFI animals showed less back fat and rump fat thickness,as well as less pelvic and kidney fat weight. Circulating leptin increased over time in all animals. Plasma leptin was greater in LRFI on 56 d and at slaughter（P = 0.0049）. Gene expression of leptin were greater in LRFI animals（P = 0.0022） in accordance with the plasma levels. The animals of the LRFI group were leaner, ate less, and had more circulating leptin and its gene expression.Conclusion： These findings demonstrated that leptin plays its physiological role in young Nellore bulls, probably controlling food intake because feed efficient animals have more leptin and lower residual feed intake.