  Background and Objective: In the current study, we sought to determine the
value of a meta-analysis to improve decision-making processes related to
nutrition in the poultry industry. To this end, nine commercial size
experiments were conducted to test the effect of a phytogenic feed additive and
three approaches were applied to the data. Materials and Methods: In all
experiments, 1-day-old male Cobb 500 chicks were used and fed corn-soybean meal
diets. Two dietary treatments were tested: T1, control diet and T2, control
diet + feed additive at a 0.05% inclusion rate. The experimental units were
broiler houses (7 experiments), floor pens (1 experiment) and cages (1
experiment). The response variables were final body weight, feed intake, feed
conversion ratio, mortality and production efficiency. Analyses of variance of
data from each and all the experiments were performed using SAS under
completely randomized non-blocked or blocked designs, respectively. The
meta-analyses were performed in R programming language. Results: No
statistically significant effects were found in the evaluated variables in any
of the independent experiments (p>0.12), nor following the application of a
block design (p>0.08). The meta-analyses showed no statistically significant
global effects in terms of final body weight (p>0.19), feed intake (p>0.23),
mortality (p>0.09), or European Production Efficiency Factor (p>0.08); however,
a positive global effect was found with respect to feed conversion ratio
(p<0.046). Conclusion: This meta-analysis demonstrated that the phytogenic feed
additive improved the efficiency of birds to convert feed to body weight (35 g
less feed per 1 kg of body weight obtained). Thus, the use of meta-analyses in
commercial-scale poultry trials can increase statistical power and as a result,
help to detect statistical differences if they exist.
