## 1 Introduction  
Pouultry (_Gallus gallus domesticus_) production on a small scale is a common practice in rural households around the world. Various studies have shown that poultry farming continues to play an important socioeconomic role in rural development [1; 2; 3].  
In Mexico, poultry production systems are developed under different agroecological and technological contexts with differences in management and production objectives; in general, they are classified into three schemes: (a) technical, (b) semi-technical, and (c) traditional or backyard; the latter channels its production to family self-sufficiency [4]. Backyard poultry farming is the most traditional and widespread activity in agricultural areas; it has been carried out since colonial times [5], it provides 85% of food security in rural productive units of the country, and it delivers high-quality food such as eggs and meat to meet essential family needs [6]. However, backyard poultry production systemsare maintained without adequate disease prevention or control strategies, inadequate management practices, and poor feeding [7].  
The supply of food for backyard poultry farming in Mexico and Latin American countries consists mainly of providing corn in its different forms and transformations, plants, and waste from the family food consumption; this type of diet does not satisfy the basic nutritional requirements of birds [8]. Feeding backyard broilers requires simple carbohydrates, fat, and protein for energy; proteins are extremely important, since their function is to provide necessary amino acids for muscle maintenance and development [9]. Therefore, all efforts are aimed at maintaining the quality of diet consumption and reducing the cost of feed to ensure maximum conversion of nutrients with high biological value [10].  
To achieve nutritional requirements in backyard broilers, family production units have sought ways to meet this nutritional demand through commercial feed(r) or diets with high protein content, therefore, production costs increase and decrease their earnings [11]. Commercial feeding represents the highest cost of poultry production, oscillating between 65 and 70% of total costs [10; 12], for which it is necessary to look for alternatives to reduce input costs without affecting the nutritional parameters in backyard broilers, likewise, they must be within the same locality and be easily obtained [11; 13; 14].  
In a study conducted by [PERSON] et al. [15] where _Agaricus bisporus_ flour was incorporated into the diet of broilers, positive results in promoting growth and antioxidant protective activity in tissues were obtained, in addition to positively affecting the intestinal health of birds. The sold-out substrate of _P. ostreatus_ has been used in the feeding of polygastric and monogastric animals [16; 17]. In this sense, various studies address that the sold-out substrate or remaining substrate of _P. ostreatus_ constitutes a source of predigested proteins, minerals, and fibers, with variations in the nutritional content of substrate, since it depends on the agricultural residue that is used to produce oyster mushrooms [18].  
Currently, edible mushrooms of genus _Pleutrotus_ are cultivated in a wide range of altitudes and have the capacity to grow in different plant residues, representing an alternative with biological, economic, and social viability for the rural population of Mexico [19]. In addition, the sold-out substrate of _P. ostreatus_ is easy to collect and handle; it also presents a high level of N, K, P, Ca, and trace elements, particularly iron and silicon [18] necessary for the growth and development of backyard broilers [10]. Therefore, the main objective of this research was focused on evaluating the effect of sold-out substrate (corn stubble) from the production of oyster mushrooms in the diet of broilers, incorporating different percentages of protein. Corn stubble is an agricultural by-product derived from the crop harvest, consisting mainly of leaves and dry stems.