The research team, based at Ferdowsi University of Mashhad in Iran, worked with 390 male Ross 308 broiler chickens divided into six treatment groups, each with five replicates of 13 birds. The birds were fed either a basal control diet or diets supplemented with a six-strain probiotic containing Lactobacillus acidophilus, Lactobacillus rhamnosus, Pediococcus acidilactici, Bacillus subtilis, Bacillus megaterium and Bacillus amyloliquefaciens at a minimum concentration of one billion colony-forming units per gram, chelated zinc at 120 milligrams per kilogram of feed, chelated copper at 150 milligrams per kilogram, or all three additives combined. To reproduce the conditions under which necrotic enteritis strikes in commercial flocks, the researchers primed the birds with a twenty-fold dose of a coccidiosis vaccine on day 11 — coccidial damage being a classic predisposing factor for the disease — and then administered an aggressive culture of C. perfringens (strain ATCC 13124) at two times ten to the eighth CFU per millilitre on days 13, 14 and 15. The experiment ran to day 21, with growth, carcass traits, gut architecture, microbial populations, blood chemistry, cecal fatty acids, meat oxidation, lesion scores and mortality all measured along the way.

The challenge worked exactly as intended. Birds exposed to C. perfringens grew significantly less than their unchallenged counterparts, finishing the 21-day period at 541 grams of cumulative body weight gain against 584 grams for the clean control group, with feed conversion deteriorating from 1.58 to 1.78 grams of feed per gram of gain. The physiological explanation is well understood: the bacterium produces toxins that erode the intestinal epithelium, triggering inflammation that diverts energy and amino acids away from muscle growth toward immune defence, while the damaged gut lining absorbs nutrients less efficiently. The challenge also left its fingerprints everywhere else in the data — breast muscle yield dropped sharply, ileal lesion scores climbed to 2.80 on a four-point scale, mortality reached 6.15 percent, and meat lipid oxidation, measured as malondialdehyde, rose to 3.10 micrograms per gram.

Against this grim backdrop, the probiotic group emerged as the single most effective intervention. Birds receiving the strain mix on top of the challenge regained nearly all the lost ground, achieving 581 grams of weight gain and posting the best early feed conversion of any challenged group. Under the microscope, the difference was striking: duodenal villus height in the probiotic group reached almost 1600 micrometres, the highest of any treatment and far above the 1121 micrometres seen in challenged, unsupplemented birds, while crypt depth fell and the villus height-to-crypt depth ratio climbed to 8.22 — a classic signature of a healthy, absorptive intestine. The probiotic also reshaped the microbial landscape, cutting ileal C. perfringens counts from 14 million to 5.5 million CFU per gram and boosting resident Bacillus populations, the very organisms best known for producing antibacterial compounds such as lichenicidin that punch holes in pathogenic cell membranes.

Chelated zinc told a complementary story. Zinc-supplemented challenged birds matched the probiotic group in body weight, and their feed intake over the full rearing period was the highest of any treatment at 985 grams. The mineral’s benefits likely stem from its well-documented role in tightening the intestinal barrier and modulating inflammation: earlier work cited by the team shows chelated zinc upregulates the anti-inflammatory cytokine IL-10 while suppressing IL-8 and other pro-inflammatory signals, restoring intestinal cell membrane integrity during infection. Zinc’s superior performance relative to inorganic sources is usually attributed to the higher bioavailability of chelated forms, which are absorbed through different pathways and place less demand on plasma albumin for transport. Ileal lesion scores in the zinc group fell to 1.60, and lipid oxidation in thigh meat dropped to 2.65 micrograms per gram, reflecting zinc’s participation in the bird’s antioxidant machinery.

Copper, by contrast, was the weakest solo performer. Birds given chelated copper grew no better than the unsupplemented challenge group over the full period and actually showed the lowest early body weight of all treatments. Yet copper was not without value: challenged birds receiving it recovered breast muscle yield to 18.53 percent of live weight, essentially matching the unchallenged control, and mortality fell to 1.53 percent. The authors note that copper’s antibacterial reputation rests largely on pharmacological doses around 250 milligrams per kilogram, considerably above the 150 milligrams per kilogram used here, which may explain the muted growth response.

The triple combination produced a genuinely mixed verdict. On several fronts it excelled: birds receiving probiotics, zinc and copper together suffered zero mortality, scored the lowest ileal lesion severity of any challenged group at 1.40, restored breast yield to 18.92 percent, and preserved jejunum architecture so well that their villus height-to-crypt depth ratio of 7.68 rivalled the healthy control. Blood biochemistry also shifted, with the combination group showing the lowest serum glucose and HDL cholesterol, consistent with altered lipid and metal metabolism when both minerals arrive in organic complexes. However, the trio failed to replicate the probiotic’s standout gains in body weight and duodenal villus height, and it delivered only intermediate results for feed intake.

The cecal short-chain fatty acid data reveal why more is not always better. Probiotic supplementation raised acetate, propionate and butyrate concentrations toward or above control levels — butyrate being the preferred fuel of enterocytes and a critical reinforcement agent for tight junctions. Zinc and copper given alone, however, sharply suppressed the fatty acid profile, with acetate falling to 25.56 and 22.50 micrograms per gram respectively. This suppression is thought to reflect the sensitivity of Lactobacillus species, key fatty-acid producers, to elevated concentrations of both metals, with copper reported in prior studies to eliminate beneficial strains such as Lactobacillus johnsonii outright. The combination group, containing the probiotic, largely avoided this pitfall, posting acetate and butyrate values statistically comparable to the control — evidence that the live microbes could partially buffer the antibacterial pressure of the minerals on the fermentative community.

The study’s overall picture is nuanced rather than triumphalist. C. perfringens unquestionably devastates growth, gut morphology, meat quality and survival, and probiotic supplementation stands out as the most consistently protective single intervention, working through competitive exclusion, organic acid production, bacteriocin release and direct architectural repair of the villi. Zinc earns its place as a robust second pillar, particularly for feed intake and barrier integrity, while copper contributes to meat yield and survival but underperforms at the dose tested. The three-way combination shines where it matters most to producers — mortality, lesion severity and breast yield — but dilutes some of the probiotic’s growth-promoting power, possibly through mineral-driven suppression of the very bacteria that make probiotics work. For an industry searching for antibiotic alternatives, the message is that nutritional strategies must be designed with their interactions in mind: the goal is not simply to stack protective additives, but to balance their antimicrobial potency against their capacity to nurture the beneficial fermenters that keep the gut — and the flock — thriving.

Subject of Research: The effects of multi-strain probiotics, chelated zinc and chelated copper on broiler chickens challenged with Clostridium perfringens.

Article Title: The Effect of Multi‐Strain Probiotics, Zinc and Copper on the Performance of Broiler Chickens Challenged With Clostridium perfringens

Article References: Kazemi, A., Kermanshahi, H., Heravi, R. M., Jouzani, G. S., & Javadmanesh, A. (2026). The Effect of Multi‐Strain Probiotics, Zinc and Copper on the Performance of Broiler Chickens Challenged With Clostridium perfringens. Veterinary Medicine and Science, 12(5), Article e71176. https://doi.org/10.1002/vms3.71176

Image Credits: AI Generated

DOI: 10.1002/vms3.71176

Keywords: necrotic enteritis, Clostridium perfringens, broiler chickens, probiotics, zinc supplementation, copper supplementation, gut health, intestinal microbiota, short-chain fatty acids, poultry nutrition, antibiotic alternatives, feed conversion ratio

The first concern centers on who was actually included in the meta-analysis. According to the commentary, the review stated that eligible participants were individuals with type 1 or type 2 diabetes mellitus, yet studies involving people with gestational diabetes and prediabetes were subsequently included in the analysis. The corresponding PROSPERO registration record, which documents the review protocol in advance, defined the eligible population simply as subjects with diabetes mellitus, without explicitly specifying these additional groups. Fuentes-Barría argues that this drift between the registered protocol and the executed review matters because gestational diabetes and prediabetes differ substantially from established type 1 and type 2 diabetes in pathophysiology, baseline cardiovascular and metabolic risk, and clinical management. Pooling these distinct populations, he contends, inflates clinical heterogeneity and weakens the applicability of the combined estimates to any single patient group.

A second and equally consequential issue involves the nature of the interventions themselves. Not all of the trials included in the meta-analysis tested zinc alone. Some interventions combined zinc with other micronutrients or bioactive compounds, a fact the original authors themselves acknowledged when they conceded that such co-interventions make it difficult to attribute observed effects specifically to zinc. The commentary argues that mixing zinc-only trials with multicomponent interventions introduces another layer of clinical heterogeneity and complicates the interpretation of pooled effects. To resolve this ambiguity, the commentator recommends sensitivity analyses that exclude multicomponent interventions, which would reveal whether the reported benefits survive when the analysis is restricted to trials in which zinc is the sole active agent. Without such analyses, he suggests, readers cannot judge the robustness of the pooled estimates or the extent to which zinc itself deserves credit.

Statistical heterogeneity represents the third pillar of the critique. The commentary highlights that several pooled outcomes showed substantial or even considerable heterogeneity across the included trials. The most striking example is plasma zinc concentration, where the I-squared statistic reached 99 percent, meaning virtually all of the variability between studies reflects real differences rather than chance. Other metabolic and inflammatory outcomes also demonstrated high heterogeneity. Although the original authors applied random-effects models and conducted meta-regression in an attempt to account for this variability, the commentary notes that substantial residual heterogeneity remained unexplained. Under these circumstances, Fuentes-Barría argues, a single pooled estimate carries limited clinical meaning, and its generalizability to diverse patient populations, dosing regimens and treatment durations should be interpreted with pronounced caution.

The fourth concern targets the meta-regression analyses themselves. The original review performed multiple meta-regressions examining age, sex, zinc dose and intervention duration as potential effect modifiers, despite several outcomes being based on a limited number of studies. This is problematic, the commentary explains, because meta-regression generally requires an adequate number of studies per moderator variable to produce reliable results. The Cochrane Handbook, the field’s leading methodological reference, advises caution when fewer than ten studies are available for such analyses. Beyond official guidance, methodological research has shown that meta-regression analyses are frequently undermined by overfitting and other pitfalls that can generate misleading findings. A meta-epidemiological study cited in the commentary found that most published meta-regressions based on aggregate data suffer from such methodological problems. Given the limited number of trials and the multiple moderators examined, the commentator concludes that these dose-response and subgroup associations should be treated as exploratory and hypothesis-generating rather than confirmatory evidence.

Perhaps the most clinically pointed criticism concerns the gap between the review’s title and its actual findings. The meta-analysis did not demonstrate significant improvements in fasting plasma glucose or HbA1c, the two canonical measures of glycemic control, despite the title emphasizing glycemic control as a primary outcome. Instead, statistically significant effects were observed primarily for surrogate markers, including circulating insulin levels, HOMA-IR as a measure of insulin resistance, C-reactive protein as an inflammatory marker, and various oxidative stress biomarkers. The commentary argues that these statistically significant shifts in surrogate endpoints should not automatically be equated with clinically meaningful improvements in diabetes control or with outcomes that matter to patients, such as reduced complications, improved quality of life or decreased mortality. Research on surrogate endpoints in diabetes trials has repeatedly shown that changes in biomarkers do not always translate into tangible clinical benefit, making this distinction far more than a semantic quibble.

The commentary’s overall message is one of measured skepticism rather than outright rejection. Fuentes-Barría explicitly frames his remarks as a constructive contribution to a clinically relevant topic, acknowledging the importance of the question the original review addressed. Zinc is an essential trace element involved in insulin synthesis, storage and secretion, as well as in antioxidant defense mechanisms, which provides a plausible biological rationale for studying its supplementation in diabetes. However, plausibility of mechanism cannot substitute for methodological rigor in the evidence synthesis that is supposed to translate biology into clinical recommendations. The commentary suggests that the enthusiasm generated by statistically significant pooled effects on biomarkers risks outpacing what the underlying trial data can actually support.

To strengthen the evidence base, the commentator proposes a concrete path forward. Stratified and sensitivity analyses by diabetes phenotype would clarify whether zinc exerts different effects in type 1 diabetes, type 2 diabetes, gestational diabetes and prediabetes, populations whose distinct metabolic contexts could plausibly modify any treatment effect. Restricting analyses to zinc-only interventions would isolate the specific contribution of the mineral from that of co-administered compounds. And prioritizing clinically relevant glycemic outcomes, particularly HbA1c and fasting glucose, over surrogate biomarkers would anchor the conclusions in endpoints that directly inform patient care. These refinements, the commentary argues, could substantially improve both the validity and the clinical interpretability of future updates to this body of evidence.

The exchange is a timely reminder of how meta-analyses, often perceived as the pinnacle of the evidence hierarchy, remain only as reliable as the methodological choices embedded within them. Decisions about which populations to pool, which interventions to combine, how to handle heterogeneity and how many moderator analyses to run can each shift the final estimates and the confidence readers place in them. For the growing number of people with diabetes worldwide who may be considering zinc supplements, and for the clinicians who advise them, the commentary underscores that the current evidence supports caution: meaningful effects on the measures that define diabetes control have not yet been demonstrated, and the significant biomarker changes reported so far should be viewed as signals worth further investigation rather than proof of clinical benefit. As the field awaits more rigorously designed and analyzed syntheses, the debate illustrates the self-correcting nature of scientific publishing, where critical commentary serves as an essential quality-control mechanism for evidence that ultimately shapes real-world health decisions.

Subject of Research: Methodological critique of a meta-analysis on zinc supplementation in diabetes

Article Title: Comment on ‘Effects of Zinc Supplementation on Glycemic Control, Insulin Resistance, Inflammation and Oxidative Stress in Diabetes’

Article References: Fuentes‐Barría, H. (2026). Comment on ‘Effects of Zinc Supplementation on Glycemic Control, Insulin Resistance, Inflammation and Oxidative Stress in Diabetes’. Endocrinology, Diabetes & Metabolism, 9(5), Article e70328. https://doi.org/10.1002/edm2.70328

Image Credits: AI Generated

DOI: 10.1002/edm2.70328

Keywords: zinc supplementation, diabetes, meta-analysis, glycemic control, insulin resistance, HbA1c, inflammation, oxidative stress, clinical heterogeneity, meta-regression, Comment, Effects