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In Sinaloa state, approximately 5 million tons of agricultural wastes are generated per year, which can be used to feed livestock. However, it is far from achieving an efficient use of these resources, since the average use of these by-products in livestock feeding approaches 45 % of the total available (SIACON-SIAP 2017). The vast majority is simply burns in the field, causing serious problems of environmental pollution, or is underused due to ignorance of its nutritional value and limitations, in terms of the response of the animals to their inclusion in the diet.
The wastes are characterized by being fibrous materials rich in structural carbohydrates of low digestibility and content of protein, minerals and vitamins. They are composed by the fraction of lower digestibility and nutritional value, because as the plant ages and finish its productive cycle, it stores in the fruit the nutrients. However, they can be used as supplements in diets or rations of ruminants, especially in critical times due to lack of forage and food (Reyes et al. 2013). They can also be used as a complement in exploitation systems, where the energy demand is lower in some productive phase of these animals.
There is a great variation in the chemical composition of the different wastes, and this, in turn, has marked effects on the degree of use by the animal, since the cell wall plays an important role in the efficiency of use of the structural polysaccharides by ruminants. This variability must be taken into account if it is desired to make a more efficient use of the nutritional potential of these wastes (Tirado, 2011).
In the region of Sinaloa state up today, there are no comprehensive chemical characterization studies of agricultural wastes, which allow determining the main differences between their bromatological characteristics. This information would allow designing adequate feeding programs for the tropical zones, when knowing the strategic nature of these by-products as an unconventional source of food.
The objective of this study was to characterize the bromatological composition of three agricultural wastes: maize (Zea mays), sorghum (Sorghum sp.) and chickpea (Cicer arietinum) from Sinaloa state, Mexico, selected for their possibilities of use in ruminants feeding.
The research was carried out in the zootechnical area and in the laboratory of animal nutrition from Facultad de Agronomía de la Universidad Autónoma de Sinaloa, México. This facility is located in the center of the state, in Culiacán municipality, at a longitude of 107° 24 'and latitude 24° 49' north and height of 62 m o.s.l. The annual average temperature is of 24.9 °C, being the minimum of 19.4 °C in January, and the maximum of 29.3 °C in May. The climate is warm and semi-dry, with an annual rainfall of 671.7 mm.
It worked with three agricultural wastes (maize, sorghum and chickpea), from Unión Ganadera Regional de Sinaloa (UGRS). This government agency is located in the capital of (Culiacán) state and is responsible for receiving in its warehouses agricultural wastes produced in the different municipalities of Sinaloa state. In order to obtain representative samples from all over the state, the wastes were sampled at random by the use of sample taker when they arrived at the storage site in the UGRS.
A total of twenty-one random samples were taken for the chemical analyzes of the wastes. The dry, unprocessed material was milled in a Thomas Willey # 4 mill, for which a 1 mm mesh sieve was used. The samples were packed in glass bottles, hermetically sealed and stored at room temperature until their analysis (Herrera et al. 1986).
The analyzes corresponding to crude protein (CP) were determined by AOAC (2016). The neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HEMI) and cellular content (CC) according to Goering and van Soest (1970).
A completely randomized design was used for the variables CP, NDF, ADF, HEMI and CC. The treatments were the wastes of maize, chickpea and sorghum. The results were processed using the Infostat statistical package (Di Rienzo et al. 2012). Duncan (1955) test was applied for means comparison (P˂0.05). The samples were analyzed in triplicate.
The results of the chemical characterization of the different wastes showed a higher CP content for the chickpea waste (figure 1). The values of the chickpea were highly significant with respect to those of maize and sorghum.
The CP results are comparable with those of Sánchez et al. (2012), when analyzing maize stubble.
However, they differ from those obtained by Aghajanzadeh et al. (2012) with chickpea straw. Generally, the CP results for agricultural wastes were low. In this regard, Serrato et al. (2013) refers the low nutritional value of these by-products, which corresponds with the results obtained in this study.
According to Macías (2015), there is great variation in the chemical composition of wastes, due to the species. The higher protein levels in chickpea waste may be related to the influence of this factor on nutritional quality. Legume straws generally contain more protein than cereal straws (Aghajanzadeh et al. 2012).
These results show that the quality, measured according to the CP content, is given by the type of forage species. Although the CP content can also vary depending on the season of the year, climate and agronomic management (Macías 2015).
The percentages of NDF, ADF, HEMI and CC of the agricultural wastes evaluated are shown in table 1. The agricultural waste of chickpea showed lower (P <0.0001) fibrous content (NDF = 68.38 %, ADF = 42.86 %) and higher cellular content (CC = 31.60 %) with respect to the rest of the evaluated materials. The maize waste was the crop residue that showed the highest (P <0.0001) cell wall content (NDF = 72.23%), lignocellulosic complex (ADF = 47.11 %) and cellular content (CC = 27.71 %).The hemicellulose (HEMI) showed no differences between treatments.
Table 1 Performance of the fibrous fractions (%) among agricultural wastes
a, b, c Means with different letters in the same row differ to P <0.05 for Duncan (1955)
The results obtained in this experiment, in terms of fibrous fractions, are comparable with those of Sánchez et al. (2012), who reported NDF contents between 70.54 and 72.04 % and 42.60 and 46.53 % of ADF for maize stubble. However, they are superior to those of Serrato et al. (2013), who reported figures of 66 % (NDF) and 40 % (ADF) for the agricultural waste of sorghum, values that are typical of foods of low nutritional quality, which can be as a complement in rations for ruminants at times of the year in which the base grass is scarce.
The developed studies allowed identifying differences from the quantitative point of view among the wastes, in terms of chemical composition. In addition, they showed that the chickpea waste had a higher nutritional quality than maize and sorghum. However, physiological studies and of interaction with the animal are necessary to determine the nutritional value and the possible differences that may exist between the wastes and its potential in ruminants feeding as an alternative of use, when the availability of nutrients is low.
