Effect of clay supplementation on growth performance of broiler chickens: a systematic review and meta-analysis

1. This review assessed the effect of dietary clay supplementation as a drug and toxin adsorbent on broiler growth performance as a meta-analysis.2. A total of 33 eligible studies were included in the present study after identification and evaluation from online databases. Standardised mean differences (SMD) with corresponding 95% confidence intervals were computed with a fixed-effects model.3. The results indicated that clay supplementation significantly improved broiler daily gain (P < 0.001) and feed conversion ratio (P < 0.001), but did not affect feed intake (P = 0.954). Results of subgroup analysis showed that zeolite clay had the most stable medium improvement effect on FCR, while kaolin had a large effect. In addition, male broilers and Cobb or Ross broilers were more sensitive to the addition of clay, and the best supplemental levels, in general, were 10 g/kg to 30 g/kg.4. Meta-regression analysis showed that clay supplemental level and sex of broilers may be important factors in the effect of clay on ADG and FCR of broilers, respectively. The sensitivity analysis showed high stability of the results and no significant publication bias was found with funnel plot analysis and Egger's or Begg's test (P > 0.05).5. In conclusion, an appropriate addition level is a prerequisite for effective clay application. Kaolin and zeolite clays seem to be more suitable for enhancing broiler growth performance, and the value of clay is amplified in specific broiler breeds.