The inclusion of exogenous phytase in P- and Ca-deficient diets of broilers to address the growing concern about excessive P excretion into the environment over the years has been remarkably documented. However, responses among these studies have been inconsistent because of the several factors affecting P utilization. For this reason, a systematic review with a meta-analysis of results from forty-one studies published from 2000 to February 2024 was evaluated to achieve the following: (1) quantitatively summarize the size of phytase effect on growth performance, bone strength and mineralization in broilers fed diets deficient in P and Ca and (2) estimate and explore the heterogeneity in the effect size of outcomes using subgroup and meta-regression analyses. The quality of the included studies was assessed using the Cochrane Collaboration’s SYRCLE risk of bias checklists for animal studies. Applying the random effects models, Hedges’ g effect size of supplemented phytase was calculated using the R software (version 4.3.3, Angel Food Cake) to determine the standardized mean difference (SMD) at a 95% confidence interval. Subgroup analysis and meta-regression were used to further explore the effect size heterogeneity (P_SMD ≤ 0.05, I² > 50%, n ≥ 10). The meta-analysis showed that supplemental phytase increases ADFI and BWG and improves FCR at each time point of growth (p < 0.0001). Additionally, phytase supplementation consistently increased tibia ash, P and Ca, and bone strength (p < 0.0001) of broilers fed P- and Ca-deficient diets. The results of the subgroup and meta-regression analyses showed that the age and strain of broiler, dietary P source, and the duration of phytase exposure significantly influence the effect size of phytase on growth and bone parameters. In conclusion, phytase can attenuate the effect of reducing dietary-available phosphorus and calcium and improve ADFI, BWG, and FCR, especially when added to starter diets. It further enhances bone ash, bone mineralization, and the bone-breaking strength of broilers, even though the effects of bone ash and strength can be maximized in the starter phase of growth. However, the effect sizes of phytase were related to the age and strain of the broiler, dietary P source, and the duration of phytase exposure rather than the dosage.

Currently, the NRC amino acid (AA) requirements for pigs published in 2012 are used as a reference in variable swine industries. However, recent results in several articles suggest that the standardized ileal digestible (SID) AA–lysine (Lys) ratio significantly evolved over the last two decades, while some publications report inconsistent outcomes. Therefore, the present study used a meta-regression analysis to assess the relative ratio to lysine to maximize the feed efficiency of four essential amino acids (tryptophan, valine, isoleucine, and methionine) in pig diets. According to the PRISMA guidelines, articles examining the target AA requirement using a basal diet supplemented with varying levels of crystalline AA (tryptophan, valine, isoleucine, or methionine) were identified across Scopus, PubMed, and Science Direct. As a result, 23, 22, 16, and 9 articles using tryptophan, valine, isoleucine, and methionine were selected and categorized into experiments for inclusion in our meta-analysis. The results suggested that the requirements of tryptophan, valine, isoleucine, and methionine in our meta-regression analysis were superior to NRC recommendations, regardless of the regression models and the growth phases with significant RSQ values (RSQ ≈ 1). Also, the QUAD and CLP regression models emphasized higher requirements than the LP model for the great majority of amino acids and growth phases. The results of the QUAD and CLP models were selected as estimations of the amino acid requirements for pigs under challenged conditions, whereas the LP model was chosen to estimate the amino acid requirements of genetically improved pigs under a modern housing system. The results of this meta-regression analysis could be used to refresh the information on the NRC amino acids (AA) requirements for swine.

Currently, the NRC amino acids (AA) requirements for pigs published in 2012 are used as a reference in variable swine industries. However, recent results in several articles suggest that the standardized ileal digestible (SID) AA: Lysine (Lys) ratio significantly evolved over the last two decades, while some publications report inconsistent outcomes. Therefore, the present study used a meta-regression analysis to assess the relative ratio to lysine to maximize the feed efficiency of four essential amino acids (tryptophan, valine, isoleucine, and methionine) in pig diets. According to the PRISMA guidelines, articles examining the target AA requirement using a basal diet supplemented with varying levels of crystalline AA (tryptophan, valine, isoleucine, or methionine) were identified across Scopus, PubMed, and Science Direct. As a result, 23, 22, 16, and 9 articles using tryptophan, valine, isoleucine, and methionine were selected and categorized into experiments for inclusion in our meta-analysis. The results suggested that the requirements of tryptophan, valine, isoleucine, and methionine in our meta-regression analysis were superior to NRC recommendations regardless of the regression models and the growth phases with significant RSQ values (RSQ ≈ 1). Also, the QUAD and CLP regression models emphasized higher requirements than the LP model for the great majority of amino acids and growth phases. The results of the QUAD and CLP models were selected as estimations of amino acid requirements for pigs under challenged conditions whereas the LP model was chosen to estimate the amino acid requirements of genetically improved pigs under a modern housing system. The results of this meta-regression analysis might be used to refresh the information on the NRC amino acids (AA) requirements for swine.

The inclusion of exogenous phytase in broiler P and Ca deficient diets in response to heightened concerns over excessive P excretion into the environment over the years has remarkably been documented. However, responses among these studies have been inconsistent because of the several factors affecting P utilization. For this reason, a systematic review with meta-analysis of results from forty-one studies published from 2000 to February 2024 was evaluated to: 1) quantitatively summarize the size of phytase effect on growth performance, bone strength, and mineralization in broilers fed P and Ca deficient basal diets and 2) estimate and explore the heterogeneity of the effect sizes of outcomes using sub-group and meta-regression analyses. The quality of the included studies was assessed using the Cochrane Collaboration’s SYRCLE Risk of Bias checklists for animal studies. Additionally, applying the random-effects models, Hedges’ g effect size of supplementation with phytase was calculated using the R software to determine the standardized mean difference (SMD) at a 95% confidence interval. Sub-group analysis and meta-regression further explored heterogeneity (P_SMD ≤ 0.05, I² > 50%, n ≥ 10). The meta-analysis showed that supplemental phytase increases ADFI and BWG and reduces FCR at each time point of growth (< 0.0001). Additionally, phytase supplementation consistently increased tibia ash, P and Ca, and bone strength (< 0.0001) of broilers fed P and Ca deficient diets. Results of the subgroup and meta-regression analyses showed that age and strain of broiler, dietary P source, and duration of phytase exposure significantly influence the effect size of phytase on growth and bone parameters. In conclusion, phytase can attenuate the effect of reducing dietary available phosphorus and calcium and improve ADFI, BWG, and reduced FCR, especially when added to starter diets. It further enhances bone ash, bone mineralization, and bone-breaking strength of broilers, even though the effects of bone ash and strength can be maximized in the starter phase of growth. However, the effect sizes of phytase were related to the age and strain of the broiler, dietary P source, and duration of phytase exposure rather than the dosage.