CATastrophic myths part 2: Common misconceptions about the environmental, nutritional, and genetic management of domestic cats and their welfare implications.

Despite the cat's popularity as a companion species, many owners and practitioners lack high quality information about important aspects of their behavior and management. Myths, anecdotes, and narratives of cats as 'low maintenance, self-sufficient' animals are pervasive, and the degree to which these may underlie complacency about fully meeting cats' needs is unknown. Several studies suggest that cat welfare and the human-cat bond may benefit from improved education about how to optimize the domestic cat's management and husbandry needs in homes and elsewhere. This paper is the second of a two-part series addressing common myths about cats. The purpose of this paper is to review and debunk common misconceptions about optimal cat care, feeding behavior, genetics, and training. Replacing these misconceptions with scientifically generated information could have a significant impact on the behavioral management of cats, positively influencing their physical health, mental stimulation, and well-being, and reducing stress for both cats and the people caring for them. Areas where further research is required to address ambiguities, and to better meet cats' needs in homes and other environments, are also identified.

The miRNA expression profile directly reflects the energy metabolic differences between slow and fast muscle with nutritional regulation of the Chinese perch (Siniperca chuatsi).

Fish skeletal muscles are composed of two distinct types, slow and fast muscles, and they play important roles in maintaining the body's movement and energy metabolism. The two types of muscle are easy to separate, so they are often used as the model system for studies on their physiological and functional characteristics. In this study, we revealed that the carbohydrate and lipid metabolic KEGG pathways are different between slow and fast muscles of Chinese perch with transcriptome analysis. In fast muscle, glucose metabolism was catabolic with higher glycolysis capacity, while in slow muscle, glucose metabolism was anabolic with more glycogen synthesis. In addition, oxidative metabolism in slow muscle was stronger than that in fast muscle. By analyzing the expression levels of 40 miRNAs involved in metabolism in the muscles of Chinese perch, 18 miRNAs were significantly upregulated and 7 were significantly downregulated in slow muscle compared with fast muscle. Based on functional enrichment analysis of their target genes, the differential expression levels of 17 miRNAs in slow and fast muscles were reflected in their carbohydrate and lipid metabolism. Among these, 15 miRNAs were associated with carbohydrate metabolism, and 6 miRNAs were associated with lipid metabolism. After 3 days of starvation, the expression levels of 15 miRNAs involved in glucose metabolism in fast and slow muscles increased. However, after 7 days of starvation, the mRNA levels of miR-22a, miR-23a, miR-133a-3p, miR-139, miR-143, miR-144, miR-181a and miR-206 decreased to basal levels. Our data suggest that the possible reason for the difference in glucose and lipid metabolism is that more miRNAs inhibit the expression of target genes in slow muscle.

Providing live black soldier fly larvae (Hermetia illucens) improves welfare while maintaining performance of piglets post-weaning.

During weaning, piglets experience concurrent social, physical, and nutritional stressors. Consequently, piglets often have poor feed intake and display increased oral manipulative behaviours post-weaning, indicative of compromised welfare. Black soldier fly larvae (BSFL) possess many attractive properties for pigs and could therefore function as effective edible enrichment, potentially alleviating weaning stress by facilitating exploration and promoting feed intake. In this study, pairs of piglets received a small amount of either live BSFL or wood shavings (8 pens/treatment) scattered throughout the pen twice a day for 11 days after weaning. Home-pen behaviour was scored by instantaneous scan sampling on day 2, 5 and 8, and behavioural responses to a novel environment and novel object were scored on day 10/11. Performance-related parameters were observed regularly. Larvae provisioning increased floor-directed exploration and decreased object-directed exploration, pig-directed oral manipulation, fighting and eating of pellets, and reduced neophobia towards a novel object. Pellet intake was significantly decreased by BSFL provisioning during day 4-11 post-weaning, although feed and net energy intake including BSFL never differed between treatments. BSFL provisioning did not influence piglet growth, feed efficiency, energy efficiency, and faecal consistency. To conclude, live BSFL provisioning positively affected post-weaning piglet behaviour while maintaining performance.

A cross-sectional study of pet owners' attitudes and intentions towards nutritional guidance received from veterinarians.

BACKGROUND: Beliefs of pet owners strongly influence their decision-making surrounding their pets' diet. Thus, nutritional guidance is an essential component of veterinary practice and integral to managing rising rates of pet obesity. This study examined pet owners' trust of, perceived effectiveness of, and intentions to follow nutritional guidance received from their veterinarian in managing their pets' diet. METHODS: A cross-sectional study of 1402 dog and cat owners in the USA and Canada was conducted using an online questionnaire tool. Data were analysed using descriptive statistics and logistic regression modelling. RESULTS: Clients are concerned about the effectiveness of veterinary nutrition recommendations. Cat owners were more likely than dog owners to consider the nutritional guidance they receive from veterinarians effective for their pets' diet (1.75, P=0.04). Length of pet ownership, feeding dry diets and frequency of veterinary visits were all positively associated with owners considering veterinary nutritional guidance to be effective in managing pets' diet. CONCLUSION: Identifying these perspectives can aid in developing strategies to provide nutrition support to pet owners to improve their perceptions of, self-efficacy with, and compliance with veterinary nutrition recommendations.

The role of polyphenols in poultry nutrition.

In the last two decades, poultry and animal industries became increasingly interested in using plant-based feed supplements, herbs and their derivatives to retain or enhance their health and productivity. These health benefits for the host mainly attributed to the secondary plant metabolites, namely polyphenols. Polyphenols are renowned for their antioxidant, immunomodulatory, anti-mutagenic and anti-inflammatory properties. However, despite these advantages of polyphenols, they have been characterized by poor absorption in the gut and low concentration in target cells that compromise their role as effective antioxidants. The low bioavailability of polyphenols necessitates the need for further investigations to harness their full potential in poultry farms. This review is existing evidence about the bioavailability of polyphenols and their antioxidant, immunomodulatory, antimicrobial, detoxification properties and their impacts on poultry performance.

Devising a new dialogue for nutrition science: how life course perspective, U-shaped thinking, whole organism thinking, and language precision contribute to our understanding of biological heterogeneity and forge a fresh advance toward precision medicine.

The process of designing and implementing individualized health-promoting interventions, nutritional or otherwise, is fraught with great difficulty owing to the heterogeneity inherent in factors that influence healthy longevity. This article proposes that careful attention to three principles-life course perspective, U-shaped thinking, and whole organism thinking-creates an attitudinal framework that can be used to reframe biological heterogeneity into the clinically relevant question: Who will benefit? The search for tools to cope with the complexity of this heterogeneity has been dominated by technological advances, including state-of-the-art "-omics" approaches and machine-based handling of "big data." Here, it is proposed that language precision and nuanced category usage could provide critical tools for coping with heterogeneity, thereby enabling interventionalists to design and implement strategies to promote healthy longevity with greater precision. The lack of a clear understanding of "Who will benefit?" stands as a major obstacle to the design and implementation of nutritional strategies to optimize healthy longevity. This article opens a new dialogue situating the principles of life course perspective, U-shaped thinking, and whole organism thinking, along with cultivating an attitude of language precision at the very core of accelerating creative discovery and refining practical advance in the field of nutrition science.

Self-selection of food ingredients and agricultural by-products by the house cricket, Acheta domesticus (Orthoptera: Gryllidae): A holistic approach to develop optimized diets.

The house cricket, Acheta domesticus L. (Orthoptera: Gryllidae) is one of the most important species of industrialized insects in the United States. Within the past five years the market of cricket powder as a food ingredient has been growing with increasing consumer interest on more sustainable sources of food. However, high labor costs of cricket production and high prices of cricket feed formulations result in cricket powder market prices much higher than other protein-rich food ingredients, making cricket powder only competitive within the novelty food market. In this study new diets formulated using by-products were developed using dietary self-selection followed by regression analysis. Crickets selected among seven different combinations of ingredients. Consumption ratios of food ingredients and by-products were used to determine macro and micro-nutrient intake. Regression analysis was used to determine the individual nutrient intake effect on cricket biomass production. Intake of vitamin C, sterol, manganese, and vitamins B1 and B5 had the most significant impact on live biomass production. Four diets were formulated based on this information and compared with a reference (Patton's 13) and a commercial diet. Although, crickets reared on Patton's diet 13 produced the most dry-weight biomass and developed the fastest, diet 4 (consisting of 92% by-products) generated the most profit (with a cost of $0.39 USD per kg) after an economic analysis that did not include the commercial formulation. Dry-weight biomass production was not significantly different among the four new diets and the commercial diet. This study demonstrated the value of dietary self-selection studies in developing oligidic insect diets and in studies of insect nutrition. This is the first such study involving farmed edible crickets and agricultural by-products. Four new cricket diet formulations contain between 62 and 92% agricultural by-products are included.

A comparison of two methods to assess apparent total tract digestibility of nutrients in dogs.

The apparent total tract digestibility (ATTD) of nutrients can be assessed by total collection of faeces (TC), which is the reference method, or by the indicator method (IM). Little information is available on proper faecal sampling methodologies for IM in canines to obtain results comparable to TC. The objective of this study was to determine the minimum number of sub-samples required for the IM to make it comparable with TC. A total of 11 adult male dogs were individually housed in metabolism cages. Dogs had access to a grass yard to facilitate defaecation. Faecal sub-samples (1/day) were taken from the daily faecal output to prepare the pooled samples for IM, obtaining cumulative sample combinations of 3 (IM3), 4 (IM4), 5 (IM5), 6 (IM6) and 7 d (IM7). Digestibility of dry matter, gross energy, crude protein and crude fibre was similar between TC and IM5, IM6 and IM7 (p > 0.05). The IM7 presented the greatest statistical similarity with TC. Nevertheless, IM was not a good predictor of crude fibre digestibility. In conclusion, IM can replace the TC method in dogs to evaluate ATTD of several nutritional fractions as long as the composite sample is collected during seven consecutive days. For estimation of fibre digestibility by IM, longer collection periods are probably required.

Progress towards pig nutrition in the last 27 years.

Over the last 27 years (1990-2017), based on the revolutionary progresses of basic nutrition research, novel methods and techniques have been developed which bring a profound technological revolution to pig production from free-range system to intensive farming all over the world. Basic theoretical innovations and feed production studies have provided vital advancements in pig nutrition by developing formula feed, utilizing balanced diets, determining feed energy value, dividing pig physiological stages, enhancing gut health, and improving feed processing technique. Formula feed is the primary contributor of the rise of the mechanized farming industry, and meets comprehensive nutritional needs of the pig. The focuses of the development of a balanced diet by optimizing nutrient levels are the amino acids balance, the balance between amino acids and energy, the balance between calcium and phosphorus. Multiple-site-production and targeted feeding program have been applied extensively. Early weaning of piglets improves production efficiency, but piglets that have not yet fully developed their intestine are prone to diarrhea. Therefore, intestinal health has received special attention in recent years. Feed processing technologies, such as granulation, puffing, fermentation and enzymatic hydrolysis, can improve the utilization of feed nutrients and reduce production cost. However, increasing a sow's potential for production, seeking alternatives to antibiotics, reducing drug treatment in piglets, developing functional additives and improving meat quality remain future challenges. Herein, we outline the important progresses of pig nutrition in the past 27 years, which will shed light on the basic nutrition rules of pig production, and help to push forward its future development. © 2018 Society of Chemical Industry.

Nutrient and AA digestibility of black soldier fly larvae differing in age using the precision-fed cecectomized rooster assay1.

Edible insects such as black soldier fly larvae (BSFL) are alternative protein sources for animal feeds due to their high-protein content and potential low environmental footprint. However, protein quality and AA content may vary across insect species and age. Our objective was to determine the effects of age on nutrient and AA digestibility of BSFL intended for use in pet foods using the precision-fed cecectomized rooster assay. All animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee prior to experimentation. Twenty-four cecectomized roosters (four roosters per substrate) were randomly assigned to test substrates [BSFL0 = day 0 (day of hatch); BSFL11 = day 11; BSFL14 = day 14; BSFL18 = day 18; BSFL23 = day 23; BSFL29 = day 29]. After 24 h of feed withdrawal, roosters were tube-fed 20 g of test substrates. Following crop intubation, excreta were collected for 48 h. Endogenous corrections for AA were made using five additional cecectomized roosters. All data were analyzed using a completely randomized design and the GLM procedure of SAS 9.4. DM and OM digestibilities were not different among substrates, but acid-hydrolyzed fat digestibility tended to be greater (P < 0.10) for BSFL23 and BSFL29 than BSFL14 and BSFL18. Although all substrates had a high digestibility, BSFL0 and BSFL11 had the lowest (P < 0.05) digestibilities for most indispensable and dispensable AA. Digestible indispensable AA score (DIAAS)-like values were calculated to determine protein quality according to AAFCO nutrient profiles and NRC recommended allowances for dogs and cats. In general, BSFL18 had the highest, and BSFL11 had the lowest DIAAS-like values for most indispensable AA. Threonine, methionine, and tryptophan were often the first-limiting AA. Our results suggest that BSFL are a high-quality protein and AA source, but that age can affect the AA digestibility and protein quality of this alternative protein source.

Phosphorus, calcium, and magnesium contents of pasture and their effect on body condition scores and body mass of communal cattle depending on natural pasture of Mogosane Village, of the North-West Province, South Africa.

This research was conducted to determine the effects of phosphorus (P), calcium (Ca), and magnesium (Mg) content in pasture with body weight and body condition scores in cattle depending entirely on natural grazing. The work was done in 2006 in Mogosane Village of North-West Province, South Africa, and it was conducted from March 2006 to March 2007, with the annual rainfall of 384.38 mm maximum. A total of 25 growing mixed breed cattle aged between 6 months and 2 years old were selected randomly from a herd feeding exclusively on communal grazing. Animals were depending on natural pasture, with no supplements given. Records of body mass (BM) and body condition score (BCS) were recorded from a diverse range of animals in order to include as many different body masses and body condition scores as possible. Mean BM and BCS values are reported but there were no significant (P > 0.05) differences between months. Possible reasons are given in the "Results and Discussion" section. The focus of the research reported here was on the changes in the P, Ca, and Mg concentrations of pasture. Pasture samples were collected once a month for analysis to determine the contents of P, Ca, and Mg. Mineral concentrations in the pasture increased significantly (P < 0.05) with rainfall in January 2007, February 2007, and March 2007, and in January 2007 and February 2007, the mean values of BCS (3.90) and BM (444.05 kg) increased. After the good rains in March 2006 and April 2006, there were significant (P < 0.05) decreases in grass P and Mg in the following dry months along with decreases in BCS and BM. There were subsequent significant (P < 0.05) increases in grass P and Mg following rains in August 2006 through January 2007. Grass Ca followed a much different pattern compared with that of P and Mg with significant (P < 0.05) increases after periods of little or no rainfall. Mineral concentrations (P, Ca, and Mg) of grass in this research were significantly (P < 0.05) influenced by the rainfall making it imperative that mineral supplementation be given to animals in the dry periods.

Recent advances in the neural regulation of feeding behavior in adult Drosophila.

The ability to maintain metabolic homeostasis is a key capability critical for the survival and well-being of animals living in constantly changing environments. Metabolic homeostasis depends on neuromodulators, such as biogenic amines, neuropeptides, and hormones, to signal changes in animals' internal metabolic status and to orchestrate their behaviors accordingly. An important example is the regulation of feeding behavior by conserved molecular and cellular mechanisms across the animal kingdom. Its relatively simple brain coupled with well-characterized genetics and behavioral paradigms makes the fruit fly Drosophila melanogaster an excellent model for investigating the neuromodulatory regulation of feeding behavior. In this review we discuss the neuromodulators and neural circuits that integrate the internal physiological status with external sensory cues and modulate feeding behavior in adult fruit flies. Studies show that various specific aspects of feeding behavior are subjected to unique neuromodulatory regulation, which permits fruit flies to maintain metabolic homeostasis effectively.

Feed supplementation with biochar may reduce poultry pathogens, including Campylobacter hepaticus, the causative agent of Spotty Liver Disease.

Increased global regulation and restrictions on the non-therapeutic use of antibiotics in the poultry industry means that there is a need to identify alternatives that prevent infection while still conveying the growth and performance benefits afforded by their use. Biochars are produced by the incomplete pyrolysis of organic materials, with reports of use as a feed supplement and activity against pathogenic bacteria. In the current study the dose-dependent effects of biochar dietary inclusion in layer diets at 1%, 2% and 4% w/w were investigated to determine a) the efficacy of biochar as an anti-pathogenic additive on the intestinal microbiota and b) the optimal inclusion level. Biochar inclusion for anti-pathogenic effects was found to be most beneficial at 2% w/w. Poultry pathogens such as Gallibacterium anatis and campylobacters, including Campylobacter hepaticus, were found to be significantly lower in biochar fed birds. A shift in microbiota was also associated with the incorporation of 2% w/w biochar in the feed in two large scale trials on two commercial layer farms. Biochar inclusion for anti-pathogenic effects was found to be most beneficial at 2% w/w. Differential effects of the timing of biochar administration (supplementation beginning at hatch or at point of lay) were also evident, with greater impact on community microbial structure at 48 weeks of age when birds were fed from hatch rather than supplemented at point of lay.

An assessment of climate change vulnerability for Important Bird Areas in the Bering Sea and Aleutian Arc.

Recently available downscaled ocean climate models for the Bering Sea and Aleutian Arc offer the opportunity to assess climate vulnerability for upper trophic level consumers such as marine birds. We analyzed seasonal and annual spatial projections from three climate models for two physical climate variables (seawater temperature and sea ice) and three forage variables (large copepods, euphausiids, and benthic infauna), comparing projected conditions from a recent time period (2003-2012) to a future time period (2030-2039). We focused the analyses on core areas within globally significant Important Bird Areas, and developed indices of the magnitude of projected change and vulnerability agreement among models. All three climate models indicated a high degree of change for seawater temperature warming (highest in the central and eastern Aleutian Islands) and ice loss (most significant in the eastern Bering Sea) across scales, and we found those changes to be significant for every species and virtually every core area assessed. There was low model agreement for the forage variables; while the majority of core areas were identified as climate vulnerable by one or more models (72% for large copepods, 73% for euphausiids, and 94% for benthic infauna), very few were agreed upon by all three models (only 6% of euphausiid-forager core areas). Based on the magnitude-agreement score, euphausiid biomass decline affected core areas for fulmars, gulls, and auklets, especially along the outer shelf and Aleutian Islands. Benthic biomass decline affected eiders along the inner shelf, and large copepod decline was significant for storm-petrels and auklets in the western Aleutians. Overall, 12% of core areas indicated climate vulnerability for all variables assessed. Modeling and interpreting biological parameters to project future dynamics remains complex; the strong signal for projected physical changes raised concerns about lagged responses such as distribution shifts, breeding failures, mortality events, and population declines.

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques.

Nitrogen is a component of essential nutrients critical for the productivity of ruminants. If excreted in excess, N is also an important environmental pollutant contributing to acid deposition, eutrophication, human respiratory problems, and climate change. The complex microbial metabolic activity in the rumen and the effect on subsequent processes in the intestines and body tissues make the study of N metabolism in ruminants challenging compared with nonruminants. Therefore, using accurate and precise measurement techniques is imperative for obtaining reliable experimental results on N utilization by ruminants and evaluating the environmental impacts of N emission mitigation techniques. Changeover design experiments are as suitable as continuous ones for studying protein metabolism in ruminant animals, except when changes in body weight or carryover effects due to treatment are expected. Adaptation following a dietary change should be allowed for at least 2 (preferably 3) wk, and extended adaptation periods may be required if body pools can temporarily supply the nutrients studied. Dietary protein degradability in the rumen and intestines are feed characteristics determining the primary AA available to the host animal. They can be estimated using in situ, in vitro, or in vivo techniques with each having inherent advantages and disadvantages. Accurate, precise, and inexpensive laboratory assays for feed protein availability are still needed. Techniques used for direct determination of rumen microbial protein synthesis are laborious and expensive, and data variability can be unacceptably large; indirect approaches have not shown the level of accuracy required for widespread adoption. Techniques for studying postruminal digestion and absorption of nitrogenous compounds, urea recycling, and mammary AA metabolism are also laborious, expensive (especially the methods that use isotopes), and results can be variable, especially the methods based on measurements of digesta or blood flow. Volatile loss of N from feces and particularly urine can be substantial during collection, processing, and analysis of excreta, compromising the accuracy of measurements of total-tract N digestion and body N balance. In studying ruminant N metabolism, nutritionists should consider the longer term fate of manure N as well. Various techniques used to determine the effects of animal nutrition on total N, ammonia- or nitrous oxide-emitting potentials, as well as plant fertilizer value, of manure are available. Overall, methods to study ruminant N metabolism have been developed over 150 yr of animal nutrition research, but many of them are laborious and impractical for application on a large number of animals. The increasing environmental concerns associated with livestock production systems necessitate more accurate and reliable methods to determine manure N emissions in the context of feed composition and ruminant N metabolism.

Effect of graded calcium supplementation in low-nutrient density feed on tibia composition and bone turnover in meat ducks.

Both genetic selection and increasing nutrient density for improving growth performance had inadvertently increased leg problems of meat ducks, which adversely affects animal welfare. We hypothesised that slowing weight gain with improving tibia quality probably enhanced tibial mechanical properties and alleviated leg deformities. Therefore, the present study aimed to evaluate the effect of graded Ca supplementation in a low-nutrient density (LND) diet on tibia composition and bone turnover in meat ducks. A total of 720 15-d-old male meat ducks were randomly assigned and fed a standard nutrient density positive control (PC) diet containing 0·9 % Ca, and four LND diets with 0·5, 0·7, 0·9 and 1·1 % Ca, respectively. Ducks fed the 0·5 % Ca LND diet and the PC diet had higher incidence of tibial dyschondroplasia (TD). When compared with the 0·5 % Ca LND diet, LND diets with ≥0·7 % Ca significantly improved tibia composition, microarchitecture and mechanical properties, and consequently decreased the incidence of TD. Furthermore, LND diets with ≥0·7 % Ca increased osteocyte-specific gene mRNA expression, blocked the expression of osteoblast differentiation marker genes including osteocalcin, collagenase-1 and alkaline phosphatase (ALP), and also decreased the expression of osteoclast differentiation genes, such as vacuolar-type H+-ATPase, cathepsin K and receptor activator of NF-κB. Meanwhile bone markers such as serum ALP, osteocalcin (both osteoblast markers) and tartrate-resistant acid phosphatase (an osteoclast marker) were significantly decreased in at least 0·7 % Ca treated groups. These findings indicated that LND diets with ≥0·7 % Ca decreased bone turnover, which subsequently increased tibia quality for 35-d-old meat ducks.

Looking for alternative animal feeds.

Josh Loeb explains how one startup company in Poland is exploring the use of invertebrates for animal feed.

Effects of environmental temperature and dietary zinc on egg production performance, egg quality and antioxidant status and expression of heat-shock proteins in tissues of broiler breeders.

To investigate the effects of environmental temperature and dietary Zn on egg production performance, egg quality and antioxidant status, as well as expression of heat-shock proteins (HSP) in tissues, of laying broiler breeders, we used a completely randomised design with a 2×3 factorial arrangement of treatments. The two environmental temperatures were normal (21±1°C, NT) and high (32±1°C, HT). The three dietary Zn sources were a Zn-unsupplemented basal diet (CON), and the basal diet supplemented with 110 mg Zn/kg as either the inorganic Zn sulphate (iZn) or the organic Zn proteinate with a moderate chelation strength (oZn). HT decreased (P<0·002) egg weight, laying rate, eggshell strength, thickness and weight, but increased (P≤0·05) rectal temperature, broken egg rate, misshapen egg rate, feed:egg ratio, Cu Zn superoxide dismutase activities in liver and pancreas, as well as metallothionein (MT) level in pancreas, and HSP70 mRNA levels in liver and pancreas of laying broiler breeders. Broiler breeders fed the oZn diet had higher (P<0·04) Zn content in the liver, as well as MT levels in the liver and pancreas, compared with those fed the CON diet. Under HT, broiler breeders fed the oZn diet had higher (P<0·05) Zn content in the pancreas compared with those fed the iZn and CON diets. The results from this study indicated that HT impaired egg production performance and eggshell quality possibly because of the disturbed redox balance and HSP homoeostasis, whereas the oZn is more available than the iZn for pancreatic Zn of heat-stressed laying broiler breeders.

Dietary arginine affects growth, gut morphology, oxidation resistance and immunity of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) juveniles.

An 8-week growth trial was conducted to evaluate the effects of dietary arginine (Arg) levels on growth, gut morphology, oxidation resistance and immunity of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) juveniles. Seven isoenergetic (1465 kJ (350 kcal)/100-g DM), isoproteic (53·5 % of DM) and isolipidic (7 % of DM) experimental diets were formulated to contain graded Arg levels ranging from 1·9 to 4·7 % (dry weight) at approximately 0·5 % increments. Each diet was randomly assigned to triplicate groups of 16 juvenile fish (average initial body weight: 11·7 (sd 0·1) g) and was administered twice daily (08.00 and 16.00 hours). After the growth trial, all remaining fish were fed their prescribed diets for 2 d and then exposed to 4·5 mg Cu2+/l water for 36 h. Results showed that growth performance and feed utilisation of experimental fish were significantly affected by different dietary Arg levels. Weight gain % (WG%) of fish was increased as dietary Arg increased, reaching a peak value at 3·8 % dietary Arg level, and when dietary Arg level increased to 4·7 % WG% was reduced. Fish fed 1·9 and 2·2 % dietary Arg levels had higher daily feed intake compared with fish fed other dietary Arg levels. Feed conversion ratios in fish fed 1·9, 2·2, 2·7 and 4·7 % dietary Arg levels were higher than those in fish fed 3·1, 3·8 and 4·1 % dietary Arg levels. Protein efficiency ratio and protein productive value (PPV) increased with an increase in dietary Arg, up to a peak value at 3·8 % dietary Arg level, above which these parameters declined. On the basis of quadratic regression analysis of weight gain % (WG%) or PPV against dietary Arg levels, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %. Fish fed 3·8 % dietary Arg had higher whole-body and muscle protein contents compared with fish fed other dietary Arg levels. Fish fed 3·8 and 4·1 % dietary Arg levels had higher levels of mRNA for insulin-like growth factor-I and target of rapamycin in the liver compared with fish fed other dietary Arg levels. Hepatic S6 kinase 1 mRNA expression in fish fed 3·8 % dietary Arg level was higher than that in fish fed any of the other dietary Arg levels. Gut morphology, hepatic antioxidant indices and immune indices in serum and head kidney were significantly influenced by dietary Arg levels. In conclusion, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %, and suitable dietary Arg supplementations improved gut morphology and oxidation resistance of hybrid grouper.