Effects of dietary chromium picolinate supplementation on broiler growth performance: A meta-analysis.

OBJECTIVE: A meta-analysis was conducted to assess the effects of dietary chromium picolinate (CrPic) supplementation on broiler growth performance and to determine whether such effects are regulated by broiler strains, sex, environmental stress, or contextual factors including study area and years. METHODS: Eligible studies were identified by searching the Web of Science, Springer, Elsevier, ScienceDirect, Taylor & Francis Online databases. Weighted average differences with corresponding 95% confidence intervals were computed with a random-effects model. We performed subgroup analysis stratified by study area, published years, broiler strains and sex, and environmental stress. Publication bias was assessed with Egger's test method. A total of 15 studies eligible for inclusion. RESULTS: The results indicated that CrPic supplementation significantly improved broiler growth performance and subgroup analysis confirmed this conclusion. We also found that Ross 308 or male broilers might be more sensitive to CrPic supplementation and showed better growth performance. A model was used to obtain the amount of chromium addition under the optimal growth performance, which suggested that the maximum value of average daily gain (ADG) was reached when chromium addition was 1810 µg/kg. The results of the sensitivity analysis showed low sensitivity and high stability of the meta-analysis. CONCLUSIONS: CrPic supplementation had a positive effect on the growth performance of broilers, and this meta-analysis provides a more accurate value of chromium addition, which may be beneficial for the practice of the broiler industry.

Meta-analysis of the correlation between dietary copper supply and broiler performance.

OBJECTIVE: To conduct a meta-analysis assessing the correlation between dietary copper supply and broiler performance. METHODS: Studies that were published prior to January 2019 and reported the dietary copper supply and broiler growth performance were identified using search functions in the Web of Science, Springer, Elsevier, Science Direct, and Taylor & Francis Online databases; the Journal of Dairy Research; and China National Knowledge Infrastructure (CNKI). We performed stratified analyses on the possible sources of bias, including differences in the study locations and years of publication. The publication bias was assessed with Egger's test method. RESULTS: A total of 12 randomized controlled trial (RCT) studies were eligible for inclusion. The pooled WMDs of the ADG, ADFI and FCR were -0.166 (95% CI: -1.587 to 1.254), -0.844 (95% CI: -1.536 to -0.152) and -0.029 (95% CI: -0.057 to 0.000), respectively. In the Israeli and Indian studies, the ADG and ADFI data in the experimental group were higher than those in the control group; however, in America, a relatively high FCR value was found in the experimental group compared to that in the control group. The analysis of the study period showed that for the 1980s and 2010s, the ADG and ADFI of the experimental group were lower than those of the control group, while, in the 1990s and 2010s, the FCR of the experimental group were lower than those of the control group. The observed values were adjusted for study effects, and a model was used to obtain the copper supplementation under the optimal production performance. The results showed that the adjusted average daily gain (ADG), average daily feed intake (ADFI), and feed to gain ratio (FCR) presented a quadratic relationship with Cu supplementation (P<0.05). The maximum value of ADG (31.84 g/d) is reached when Cu is added at amount of 158 mg/kg, and the minimum value of FCR (1.53) is reached when Cu is added at amount of 217 mg/kg. No significant publication bias existed in the studies (Egger's test: P value were 0.81, 0.71 and 0.14). CONCLUSION: From this study, it can be concluded that the traditional copper addition is no longer suitable for modern broiler breeding; the higher copper content may be beneficial for the production performance of broilers.