## 2 Materials and Methods
### Experimental Design and Diets  
Care and management of birds were agreed upon and approved by the Bioethics Committee of Facultad de Medicina Veteraria y Zootecnia, and the Posgrado en Manejo Sustentable de Agroecosistemas of Benemerita Universidad Autonoma de Puebla (FACMEDVET/CI2021-2022).  
The sold-out substrate of _P. ostreatus_ (from corn stubble) was subjected to particle reduction with the help of a manual mill, until reaching an approximate size of 0.5 mm, which was incorporated into the different experimental diets in the growth and completion stage.  
The dietary experiment (pilot study) was conducted on 120 Ross 308 broilers from a commercial hatchery; 10-day-old male chicks were vaccinated with Tabel VH(r) against Newcastle disease (1 drop per eye per bird) and TAbic H-120 Var(r) against avian influenza (0.5 mL/bird) [27]. Commercial feed(r) was supplied in the initiation stage, from day 1 to 28 days of age, reaching an average weight per bird of 0.48 \(\pm\) 0.01 g. The commercial feed(r) contains 20.16% protein that provides 3275 (kcal/kg) of metabolizable energy, necessary for the nutritional contribution of broilers (Table 1).  
For the growth and finishing stage, the broilers were housed in groups of 10 birds in 12 pens with a concrete floor and curly shaving bedding with an area of 3 m\({}^{2}\) each, with a density of 3.32 birds/m\({}^{2}\), equipped with an automatic bell-type drinker and tubular feeder [28]. The distribution of the experimental flock was randomized following a completely randomized design in 4 groups of 10 broilers, with three repetitions per treatment.  
The diets were divided into a control treatment (\(n=30\)) based on commercial feed(r); treatment T1 (\(n=30\)) based on sold-out substrate, wheat germ, and corn tortilla; treatment T2 (\(n=30\)) based on sold-out substrate and wheat germ, and T3 treatment (\(n=30\)) based on wheat germ and corn tortilla (Table 2), according to the calculations made through the Pearson square; this being a practical method when mixing two or more foods that have different concentrations of protein [29]. Metabolic energy was calculated for feed components based on the results of chemical analyses, prior to formulating dietary recipes, based on poultry recommendation guidelines for birds (Table 2).  
From four weeks onwards, the broilers began to be fed with different diets (Figure 1) and free access to water; every 24 h, the pens were cleaned of food remains until reaching 70 days of the experiment. Every 15 days, the sawdust bed was changed and new curly shaving bedding was placed.  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Ingredient** & **(g)** \\ \hline Sorghum & 54.00 \\ Soya flour & 21.00 \\ Meat flour & 8.00 \\ Peanut flour & 9.47 \\ Soy oil & 5.23 \\ Common iodized salt & 0.20 \\ DL-Methionine & 0.25 \\ Pecutrin & 1.42 \\ Biolys & 0.43 \\ Total (g) & 100.00 \\ Crude protein (\%) & 22.16 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Ingredients contained in the commercial feed® for the starter stage for broilers.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Ingredient** & **TC** & **T1** & **T2** & **T3** \\ \hline Commercial feed® (g) & 100.00 & - & - & - \\ Wheat germ (g) & - & 50.00 & 50.00 & 50.00 \\ Sold-out substrate (g) & - & 25.00 & 50.00 & - \\ Corn tortilla (g) & - & 25.00 & - & 50.00 \\ Total (g) & 100.00 & 100.00 & 100.00 & 100.00 \\ Crude protein (\%) & 20.16 & 20.26 & 19.64 & 20.89 \\ Carbohydrate (\%) & 70.00 & 62.84 & 59.19 & 66.50 \\ Fat (\%) & 8.50 & 6.19 & 5.53 & 6.85 \\ Moisture (\%) & 12.00 & 6.25 & 6.51 & 5.99 \\ Crude fiber (\%) & 8.00 & 8.71 & 12.29 & 5.12 \\ Ash (\%) & 5.00 & 7.82 & 12.31 & 3.34 \\ Metabolizable energy (kcal/kg) & 3275.00 & 2946.74 & 3032.90 & 2861.10 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Experimental dietary ingredient content, metabolizable energy value, and crude protein percentage essential for broiler feeding.