This study evaluated the effects of partially replacing soybean meal with Tenebrio molitor larvae meal (TMM) at dietary inclusion levels of 0%, 2%, 5%, and 8% in finisher diets fed to 180 broiler chickens (22–42 days). Growth performance was monitored during the finisher phase, and breast meat from the same birds was analyzed for sensory and physicochemical quality. Sensory evaluation was performed by a consumer panel of 92 participants. No significant differences were observed in body weight gain, feed intake, or feed conversion ratio, confirming the nutritional feasibility of TMM inclusion up to 8%. Sensory evaluation showed that appearance and aroma were unaffected, while juiciness, flavor, tenderness, and texture decreased at inclusion levels ≥5%, indicating a threshold effect. Despite this reduction, all sensory scores remained within acceptable ranges for consumer preference. Physicochemical parameters, including acidity, water activity, thawing loss, and cooking loss, were not significantly influenced by dietary treatment. Minor variations in pH were detected but remained within the physiological range reported for broiler breast meat and did not compromise overall meat quality. Overall, TMM can replace soybean meal at inclusion levels up to 8% in finisher broiler diets without adversely affecting growth performance or physicochemical meat quality. However, because sensory attributes declined at inclusion levels ≥5%, dietary inclusion of TMM below 5% is recommended when maintaining sensory quality is a primary objective. Beyond its nutritional benefits, the partial replacement of soybean meal with TMM may contribute to diversifying protein sources for poultry nutrition and reducing reliance on conventional soybean-derived ingredients, thereby contributing to the development of more sustainable poultry production systems.

Reducing crude protein in amino acid-adequate diets for broiler chickens is effective in reducing nitrogenous emissions and competition for resources between the food and feed sectors. This review provides a comprehensive analysis of the literature on the relevance of nonessential amino acids in low protein diets for broiler chickens. Glycine and serine, owing to their interconvertibility summarised as glycine equivalents (Glyequi), limit growth when dietary crude protein is reduced below 19% in up to 3-week-old birds. Considering essential amino acids and the variable Glyequi requirements enables the reduction of dietary crude protein to ∼16% without compromising growth. Variation in Glyequi requirements likely occurs predominantly from the varying amounts of uric acid formed. Other influences seem to exert lower impacts on dietary Glyequi requirements. Asparagine or glutamine is probably the growth-limiting amino acid when crude protein is reduced below 16%. Alternatively, nonspecific amino-nitrogen may be lacking in such diets. The current potential to reduce dietary crude protein when using free essential and nonessential amino acids enables to increase the efficiency of nitrogen utilisation to a value above 80%. This coincides with reduced uric acid synthesis and energy expenditure for nitrogen excretion. The lower nitrogen excretion via the urine results in a lower energy expenditure. Hence, dietary energy may prospectively be reduced once the energy-sparing effect is quantified, thereby further reducing the competition for resources between food and feed.

The effect of the supplementation of γ-aminobutyric acid (GABA), a component of the neuroendocrine cascade involved in stress alleviation, was studied in broiler chickens in a heat stress model. In a 42-day feeding trial, 300 male and 300 female broiler chickens were equally distributed in an environmentally controlled and an open house (OH) according to a 2 × 2 × 3 factorial design. The diet was either devoid of GABA (0 mg/kg) or was supplemented with 60 or 120 mg/kg GABA. Zootechnical performances (1–42 days), expression of mRNA for genes coding for inflammatory cytokines (IL-1β, IL-8, TNF-α) in the spleen (24 days), oxidative regulators (Nrf-2, superoxide dismutase) in the liver (24 days) and arterial blood gas concentrations (24 days) were assessed. Whole genome sequencing of the caecal microbiome was performed for the male birds (42 days). Supplementation of GABA improved (P < 0.01) body weight and feed conversion ratio irrespective of sex and housing conditions, expression of IL-1β and IL-8 and Nrf-2 gene. GABA decreased (P < 0.05) malondialdehyde and increased (P < 0.05) glutathione peroxidase activities in serum. GABA decreased circulatory corticosterone concertation (P < 0.05). While both housing conditions benefitted from GABA, its effects were more pronounced in OH (house effect P < 0.05). GABA supplementation modulated caecal microbiota composition by increasing the relative abundance of beneficial bacteria such as Alistipes and Bacteroides, particularly in the OH environment. Overall, this study concludes that 60 mg/kg GABA supplementation improves growth performance, stress resilience and microbial composition in broiler chickens, with variable effects depending on housing conditions.

Reducing dietary crude protein (CP) concentration while maintaining adequate amino acid (AA) supply by free AA inclusion can contribute to attenuate the negative environmental effects of animal farming. This study investigated upper limits of dietary free AA inclusions without undesirable effects including the dependence on asparagine (Asn) and glutamine (Gln) supply. Ten broilers were allocated to sixty-three metabolism units each and offered nine experimental diets from day (d) 7–21 (n 7). One diet (167 g CP/kg) contained 80 g soya protein isolate (SPI)/kg. In the other diets, 25, 50, 75 and 100 % of the digestible AA from SPI were substituted with free AA. Digestible Asn+aspartic acid (Asp) and Gln+glutamic acid (Glu) were substituted with Asp/Glu or 50/50 mixes of Asp/Asn and Glu/Gln, respectively. Total excreta were collected from d 11–14 and from d 18–21. Growth and nitrogen accretion were unaffected by 25 and 50 % substitution without and with free Asn/Gln, respectively, but decreased at higher substitution (P ≤ 0·024). Circulating concentrations of Asp, Glu and Gln were unaffected by treatment, while Asn decreased at substitution higher than 50 % when Asn/Gln were not provided (P ≤ 0·005). Blood gas analysis on d 21 indicated a compensated metabolic acidosis at substitution higher than 50 and 75 % without and with free Asn/Gln, respectively (P ≤ 0·017). Results suggest that adding Asn/Gln increased an upper limit for proportion of dietary free AA from 10 to 19 % of dietary CP and enabled higher free AA inclusion without affecting the acid–base balance.

Characterisation of the effect of transport on the welfare of fowl requires common currency methods that can compare the effects of diverse stressors using the same unit of measure. Aversion of broiler chickens (42 ± 1 days old) to vibrational and thermal stressors was investigated in a continuous free-choice procedure. Each choice-chamber had four compartments, connected via a central zone, offering a thermal stressor (T: 40°C, relative humidity 21%), a vibrational stressor (V: 2 Hz, 1 ms−2), concurrent vibrational and thermal stressors (VT), or no applied stressors (N). In experiment 1, there were no significant effects of stressor on the latency to leave the compartments after initial introduction (n = 24). In experiment 2, 12 subjects were introduced individually to a chamber for 4 h during each of a control and two treatment sessions. The results indicated that chickens did not avoid vibration, but significantly avoided the thermal stressor overall (T and VT; P < 0.001). As no interactive effect of the stressors was observed, all avoidance of the combined stressors can be attributed to the effects of the thermal stressor alone. Further work is required to establish ways in which delayed stressors can be studied using behavioural methods before common currency methods can be practicable.

This paper reports results from two workshops held in York, England that investigated public attitudes towards the welfare of broiler chickens. At the outset the majority of participants admitted that they knew little about how broiler chickens are reared and were shocked at some of the facts presented to them. Cognitive mapping and aspects of Q methodology were used to reveal the range of variables that participants believed affected chicken welfare, the causal relationships between those variables, and what variables were considered most and least important. While some participants focused on the importance of meeting basic needs such as access to food, water, light and ventilation, others highlighted the role of welfare regulations and public opinion. Factor analysis of the results from a ranking exercise identified two factor groups, ‘Factor one; the bigger picture’ and ‘Factor two; basic animal needs’. The findings demonstrate that some members of the public are both interested in learning about how their food is produced and concerned about the conditions faced by broiler chickens. Some are able to see clear links between public opinion and the welfare of farm animals; an important connection if consumer behaviour is to contribute towards improving animal welfare.

The behaviour of broilers reared at pasture from 4 to 12 weeks of age on a low density diet supplied either indoors or outdoors, was compared with that of birds reared inside on deep litter. This single study found few differences in behaviour. Activity levels of birds outside were initially greater, but from six weeks of age lying increased to comparable levels in all groups.

Surprisingly little use was made of the extra space and facilities such as perches at pasture. It is proposed that the main reason for this was leg weakness as 80 per cent of the birds had a detectable gait abnormality at seven weeks of age. There was no evidence of reduced motivation to extend the behavioural repertoire, as, for example, ground pecking remained at significantly higher levels in the outdoor groups because it could also be performed from a lying posture.

Fast-growing broiler chickens use pen-space heterogeneously and have low activity levels, related in part to leg problems. The aim of this study was to test the effects of the addition of string and sand trays to rearing pens on the use of space, levels of activity and leg problems. Broiler chickens were reared in 12 pens (40 birds per pen). Drinkers and feeders only were present in the six control pens (C group), whereas the six other pens were enriched (E group) with two sand trays and string. Behaviour was recorded by scan and focal sampling on days 2-3, 13-14, 23-24 and 34-35. Bodyweight, the occurrence of tarsal deformities and the composition of tibiotarsi were measured on day 37. Chickens from the E group spent more time and stood more often in the area enriched with sand than did the g group birds. ghickens in the E group foraged in the sand throughout the rearing period, and their foraging activities were greater than those of the C group birds. They had little interest in the strings. Locomotor activity during standing bouts was enhanced in the E group on days 2-3 only. Bodyweight at day 37, the occurrence of tarsal deformities and the composition of tibiotarsi were not significantly different between groups. These results indicate that sand could attract chickens into areas that are usually rarely used, which may reduce problems resulting from their heterogeneous distribution. However, the results also indicate the difficulty of stimulating locomotion.

Commercially reared broiler chickens are commonly supplied with drinking water through lines of nipple drinkers that are positioned above the birds' heads to avoid water leaking and spoiling the litter underfoot. This means that the birds have to peck upwards to obtain water, an action that is very different from the ‘scoop’ action of natural drinking seen when birds drink from troughs or puddles. In this study we investigate the welfare implications of this unnatural drinking behaviour imposed by nipple drinkers. We show 1) that chickens have no apparent aversion to the taste of tap water, 2) that they prefer bell drinkers and troughs over nipple drinkers, 3) that the stereotyped ‘scoop’ action is seen even when birds are drinking from bowls of different heights, 4) that chickens have a strong preference for drinking from nipples that are lower rather than higher and, 5) that when offered a choice between bowls and nipples of the same height, the chickens are indifferent to the method of water presentation. We conclude that the height at which water is presented to chickens is more important to them than whether they can drink with the natural ‘scoop’ action. While this might suggest that chicken welfare could be improved by lowering the drinker lines, wet litter causes welfare issues of its own through its effect on hock burn and pododermatitis. We suggest that drinker systems should be designed so that both aspects of welfare (birds able to drink in their preferred way and clean litter) are possible.

Leg disorders are a major cause of poor welfare in broilers. Previous studies have shown that at slaughter age at least 90% of chickens experienced some degree of gait problems and approximately 30% were seriously lame. In this study, a new and non-invasive technique was developed to automatically assess the lameness of the birds. For this purpose, video surveillance images of broilers with five different pre-defined gait scores were recorded as they walked along a test corridor. Afterwards, the image-processing algorithm was applied to detect the number of lying events (NOL) and latency to lie down (LTL) of broiler chickens. Then, the results of the algorithm were compared with visually assessed manual labelling data (reference method) and the relation between these measures and lameness was investigated. Eighty-three percent of NOL were correctly classified by the automatic monitoring system when compared to manual labelling using a data set collected from 250 broiler chickens. The results also showed a positive significant correlation between NOL and gait score and a significant negative correlation between LTL and gait-score level of broilers. Since strong correlations were found, on the one hand, between two measures and gait-score level of broiler chickens and, on the other, between the results of algorithm and manual labelling, the results suggest this automatic monitoring system may have the potential to be used as a tool for assessing lameness of broiler chickens.

Genetics is key to the improvement of welfare in broiler chickens at both juvenile and adult (breeder) stages but progress is hampered currently by the seemingly conflicting demands of welfare, commercial production, food security and calls for increasing intensification to curb climate change. Animal welfare is therefore most likely to be improved on a commercial scale by future breeding programmes that incorporate multiple goals of different stakeholders as far as possible and give higher priority to animal welfare. These include: i) broilers with high welfare traits; ii) broiler breeders that do not need feed restriction; iii) birds that can be grown in an economically profitable way; iv) birds with low disease levels without the need for routine medication; v) chicken meat that is healthy and good for humans to eat; and (vi) broilers and breeders that thrive in systems that are environmentally sustainable. Progress towards achieving these goals is hampered currently by the assumptions that high juvenile growth rate is incompatible with good welfare and that feed restriction in adults is inevitable with fast-growing juveniles. We challenge these assumptions at both genetic and whole-animal level and argue that the conflict between good welfare and productivity can be reduced by making use of all available genetic variation from existing breeds and other sources and selecting birds in the range of environments they will encounter in commercial production.

There is dearth information on the role of fisetin as an antistress agent in ameliorating heat stress in broiler chickens. Here, we experimentally compared probiotic, an antioxidant and antistress agent, with fisetin, an antioxidant agent with little or no report on its antistress effect. Sixty-day-old broiler chickens (Arbo Acre breed) were allotted into 4 groups of 15 birds each as follows; control, fisetin, probiotic, and fisetin + probiotic groups, respectively. All administrations were performed orally through gavage for the treatment groups. The environmental and cloacal temperature (CT) parameters were measured bi-hourly at Days 21, 28, and 35 from 7:00 to 7:00 hr, during the period of study. The environmental parameters exceeded the thermoneutral zone for broiler chickens. The probiotic-supplemented group had the least overall mean CT values all through the experimental period. Based on our findings, fisetin was not a potent antistress agent in mitigating heat stress in birds.

Nutrition in early life has a long-term influence on later health. In order to the explore effects of in ovo feeding (IOF) of vitamin C on splenic development, splenic metabolism and apoptosis were detected in embryo, adult chickens and in vitro. A total of 360 fertile eggs were selected and randomly assigned to control (CON) and vitamin C (VC) groups which were injected with saline and vitamin C on embryonic day 11, respectively. Functional enrichment of differentially expressed genes by transcriptome on embryonic day 19 suggested that purine nucleotide metabolism might be a potential pathway for the IOF of vitamin C to regulate spleen development. Additionally, the IOF of vitamin C significantly increased splenic vitamin C content on post-hatch day 21. Meanwhile, the splenic expression of adenosine deaminase, serine/threonine kinase 1 and proliferating cell nuclear antigen was down-regulated, whereas the expression of cysteinyl aspartate specific proteinase 9 was up-regulated in the VC group. On post-hatch day 42, the IOF of vitamin C significantly down-regulated the splenic expression of B-cell lymphoma 2 and increased the mRNA level of cysteinyl aspartate specific proteinase 9. The IOF of vitamin C could regulate the expression of genes related to adenylate metabolism and increased the apoptosis rate in vitro, which is consistent with the result in vivo. In conclusion, the IOF of vitamin C regulated splenic development and maturation by affecting purine nucleotide metabolism pathway and promoting apoptosis.

Chickens adapt to P and Ca restriction during the very first days of life by improving P utilisation efficiency. The present study was built to identify the mechanisms underlying this adaptive capacity, and to identify the optimal window of application of the restriction (depletion). A total of 1600 Cobb 500TM male broilers were used. During each phase (from age 0 to 4 d, 5 to 8 d, 9 to 18 d and 19 to 33 d), the animals received either a control diet (H) or a restricted diet (L) with reduced levels of non-phytate P (nPP) and Ca (between −14 and −25 % for both) with four dietary sequences: HHHH, HLHL, LHHL and LLHL. None of the feeding strategies affected growth. Tibia ash content at day 4 and 8 was impaired when the L diet was fed from 0 to 4 and 5 to 8 d, respectively (P = 0⋅038 and P = 0⋅005). Whatever the early restriction period or length between 0 and 8 d of age, the mineralisation delay was compensated by day 18. This was accompanied by an increased mRNA expression of the Ca transporter, CALB1, and an increased apparent ileal digestibility of Ca at day 8 (P < 0⋅001). This adaptation was limited to the starter phase in restricted birds. No effect was seen on P transporters mRNA or protein expression. In conclusion, birds adapted to mineral restriction by increasing Ca and nPP utilisation efficiencies. Depletion−repletion strategies are promising in improving the sustainability of broiler production but need to be validated in phytase-supplemented diets.

The objective of this systematic review was to evaluate the efficacy of antibiotics to prevent or control colibacillosis in broilers. Studies found eligible were conducted controlled trials in broilers that evaluated an antibiotic intervention, with at least one of the following outcomes: mortality, feed conversion ratio (FCR), condemnations at slaughter, or total antibiotic use. Four electronic databases plus the gray literature were searched. Abstracts were screened for eligibility and data were extracted from eligible trials. Risk of bias was evaluated.

Seven trials reported eligible outcomes in a format that allowed data extraction; all reported results for FCR and one also reported mortality. Due to the heterogeneity in the interventions and outcomes evaluated, it was not feasible to conduct meta-analysis.

Qualitatively, for FCR, comparisons between an antibiotic and an alternative product did not show a significant benefit for either. Some of the comparisons between an antibiotic and a no-treatment placebo showed a numerical benefit to antibiotics, but with wide confidence intervals. The risk-of-bias assessment revealed concerns with reporting of key trial features.

The results of this review do not provide compelling evidence for or against the efficacy of antibiotics for the control of colibacillosis.

A 42-d study was conducted to investigate the effects of an emulsifier supplementation (de-oiled soyabean lecithin (DSL)) of diets with different levels of metabolisable energy (ME) and various sources of fat on growth performance, nutrient digestibility, blood profile and jejunal morphology of broiler chickens. Diets were arranged factorially (2 × 2 × 2) and consisted of two concentrations of ME (normal and low), two fat sources (soyabean oil (SO) and poultry fat (PF)) and two levels of DSL supplementation (0 and 1 g/kg). A total of 800 1-d-old male broiler chickens were assigned to eight treatments with five replicates/treatment. The results showed the supplemental DSL caused improvements in the overall feed conversion ratio, fat digestibility and jejunal villus height:crypt depth ratio, but the magnitude of the responses was greater in the PF-containing diets, resulting in significant fat × DSL interactions (P<0·05). Abdominal fat percentage was also reduced by the PF-containing diet, but the response was greater in the normal ME diet, resulting in a significant ME × fat interaction (P = 0·048). Dietary DSL supplementation also increased nitrogen-corrected apparent ME values but decreased blood TAG (P = 0·041) and LDL (P = 0·049) concentrations, regardless of the source of fat used or the ME values in the diet. In conclusion, the present study suggests that the improvements in growth performance, fat digestibility and intestinal morphology that can be achieved with DSL supplementation are highly dependent on the degree of saturation of lipid incorporated into broiler chicken diets.

Coccidial infections reduce fat-soluble vitamin status and bone mineralisation in broiler chickens. We hypothesised that broilers infected with Eimeria maxima would benefit from increased dietary supplementation with vitamin D (vitD) or with 25-hydroxycholecalciferol (25(OH)D3 or 25D3). Broilers were assigned to diets with low (L) or commercial (M) vitD levels (25 v. 100 μg/kg) supplemented as cholecalciferol (D3) or 25D3. At day 11 of age, birds were inoculated with water or 7000 E. maxima oocysts. Pen performance was calculated over the early (days 1–6), acute (days 7–10) and recovery periods (days 11–14) post-infection (pi). At the end of each period, six birds per treatment were dissected to assess long bone mineralisation, plasma levels of 25D3, Ca and P, and intestinal histomorphometry. Parasite replication and transcription of cytokines IL-10 and interferon-γ (IFN-γ) were assessed at day 6 pi using quantitative PCR. Performance, bone mineralisation and plasma 25D3 levels were significantly reduced during infection (P < 0·05). M diets or diets with 25D3 raised plasma 25D3, improved performance and mineralisation (P < 0·05). Offering L diets compromised feed efficiency pi, reduced femur breaking strength and plasma P levels at day 10 pi in infected birds (P < 0·05). Contrastingly, offering M diets or diets with 25D3 resulted in higher parasite loads (P < 0·001) and reduced jejunal villi length at day 10 pi (P < 0·01), with no effect on IL-10 or IFN-γ transcription. Diets with M levels or 25D3 improved performance and mineralisation, irrespective of infection, while M levels further improved feed efficiency and mineralisation in the presence of coccidiosis.

Finding insect meals as alternative sources of poultry feedstuffs is a recent research topic; therefore, the present study aimed to evaluate the effects of defatted black soldier fly (Hermetia illucens L., HI) larvae meal in broiler chicken diets on the carcass characteristics and meat quality parameters, proximate composition, fatty acid profile and the heavy metal content of the breast meat. Four dietary treatments were designed: a control diet (HI0) and three experimental diets (HI5, HI10 and HI15), corresponding to 50, 100 and 150 g/kg HI inclusion levels, respectively. The inclusion of 50, 100 and 150 g HI meal per kg feed supply 16.56%, 33.01% and 49.63% of required crude protein. The broilers were slaughtered at day 35, the carcasses were weighed and the breast muscles were excised from 16 birds per each feeding group (two birds per replicate pens) and used for meat quality evaluation. Linear and quadratic responses were observed, for increasing HI meal levels, in the live and carcass weights (maximum for HI10). As far as the colour of the breast meat is concerned, redness (a*) showed a linear response, while yellowness (b*) linearly decreased with increasing HI meal levels (minimum for HI15). As the HI larvae meal increased in the diets, the moisture content linearly decreased and the protein content increased. The total saturated fatty acid and total monounsaturated fatty acid proportions rose to the detriment of the polyunsaturated fatty acid fraction. The HI larvae meal, used in the current study, represents a valuable protein source for broiler chickens when included by up to 100 g/kg in their diets, as an improved slaughtering performance was observed without any detrimental effects on meat quality parameters or heavy metal residues in the meat.

This experiment was conducted to investigate the effects of guanidinoacetic acid (GAA) on productive performance, intestinal morphometric features, blood parameters and energy utilisation in broiler chickens. A total of 390 male broiler chicks (Ross 308) were assigned to six dietary treatments based on a factorial arrangement (2×3) across 1–15 and 15–35-d periods. Experimental treatments consisted of two basal diets with standard (STD; starter: 12·56 MJ/kg and grower: 12·97 MJ/kg) and reduction (LME; starter: 11·93 MJ/kg and grower: 12·33 MJ/kg) of apparent metabolisable energy (AME) requirement of broiler chickens each supplemented with 0, 0·6 and 1·2 g/kg GAA. Supplemental 1·2 g/kg GAA decreased the negative effects of feed energy reduction on weight gain across starter, growing and the entire production phases (P<0·05). Energy retention as fat and total energy retention were increased when birds received LME diets supplemented with 1·2 g/kg GAA (P<0·05). Net energy for production (NEp) and total heat production increased in birds fed LME diets containing 1·2 g/kg GAA (P<0·05). A significant correlation was observed between dietary NEp and weight gain of broilers (r 0·493; P=0·0055), whereas this relationship was not seen with AME. Jejunal villus height and crypt depth were lower in birds fed LME diets (P<0·05). Serum concentration of creatinine increased in broilers fed LME diets either supplemented with 1·2 g/kg GAA or without GAA supplementation (P<0·05). Supplemental GAA improved performance of chickens fed LME diet possibly through enhanced dietary NEp. The NEp could be preferred over the AME to assess response of broiler chickens to dietary GAA supplementation.

The objective of the present study was to evaluate the effects of partial or total replacement of finisher diet soybean oil with black soldier fly (Hermethia illucens L.; HI) larva fat on the growth performance, carcass traits, blood parameters, intestinal morphology and histological features of broiler chickens. At 21 days of age, a total of 120 male broiler chickens (Ross 308) were randomly allocated to three experimental groups (five replicates and eight birds/pen). To a basal control diet (C; 68.7 g/kg as fed of soybean oil), either 50% or 100% of the soybean oil was replaced with HI larva fat (HI50 and HI100 group, respectively). Growth performance was evaluated throughout the trial. At day 48, 15 birds (three birds/pen) per group were slaughtered at a commercial abattoir. Carcass yield and proportions of carcass elements were recorded. Blood samples were taken from each slaughtered chicken for haematochemical index determination. Morphometric analyses were performed on the duodenum, jejunum and ileum. Samples of liver, spleen, thymus, bursa of fabricius, kidney and heart were submitted to histological investigations. Growth performance, carcass traits, haematochemical parameters and gut morphometric indexes were not influenced by the dietary inclusion of HI larva fat. Histopathological alterations developed in the spleen, thymus, bursa of fabricius and liver and were identified in all of the experimental groups, but HI larva fat inclusion did not significantly affect (P>0.05) the severity of the histopathological findings. The present study suggests that 50% or 100% replacement of soybean oil with HI larva fat in broiler chickens diets has no adverse effects on growth performance or blood parameters and had no beneficial effect on gut health.