INTRODUCTION

In the last 30 years the summer pastures dedicated to livestock production in the State of Sonora, Mexico, has a great floristic diversity of non-timber and timber plants. Between 30% to 70% of the native and high forage species that currently have a strong decrease in their populations, are palo fierro (Olneya tesota A. Gray), zámota (Coursetia glandulosa A. Gray), cósahui (Krameria erecta Willd), among others, because they have had a notable consumption by herbivores; coupled with the massive clearings and the change in land use, it has not allowed them to spread naturally; so they are in serious problems that could lead them to disappear from their own ecosystems (^{Mc Caughey-Espinoza et al., 2017}). Shrubs constitute a good percentage of the diet of bovine animals, so it is important to conserve native plants in natural habitats. The nutritional value of food is given by its chemical composition and the efficiency with which animals extract their nutrients during digestion (^{Sanon et al., 2008}).

Forage plants form the basis of cattle feeding, provide the fundamental nutrients to meet the physiological requirements of animals. Native plants provide a diet rich in protein, phosphorus and calcium, at different seasons of the year. It is of the utmost importance to investigate the forage resources of the environment, to incorporate them into livestock production systems and provide sustainable alternatives that allow improving the agro- ecosystems and living conditions of the communities (^{Francis and Lowe, 2000}; ^{Muñoz et al., 2011}; ^{Apráez et al., 2017}).

Trees and associated shrubs provide multiple benefits to livestock (^{Ruiz et al., 2006}). Native drought-tolerant fodder plants are options to improve the nutritional deficiencies of grazing cattle (^{Insuasty et al., 2013}), due to their great versatility and various benefits; they are very important in agroforestry and silvopastoral systems (^{Portillo et al., 2009}). It has also been attributed medicinal benefits, showing effects against liver damage, antioxidant, anti-inflammatory and anti-cancer (^{Carini et al., 2002}; ^{Torres-González et al., 2011}; ^{Jiménez-Estrada et al., 2013}; ^{Morán-Palacio et al., 2014}).

At present, livestock activity merits a new productive approach that revalues tree and shrub resources, as fundamental elements for the design of efficient and sustainable production systems. Therefore, in this investigation, a chemical analysis of the southern cósahui (Krameria erecta) was proposed, due to the forage potential that this species represents for the summer pastures of the state of Sonora, Mexico.

MATERIAL AND METHODS

Location of the study area

The present work was carried out in the ranch "Las Cruces" located in the eastern part of Hermosillo, Sonora; located at 29° 03’21.30” from North Latitude and 110° 45'12022" from West Longitude, at an altitude of 277 meters above sea level, with an average annual rainfall of 330 mm and an average temperature of 24 °C, with vegetation called arbosufrutescent scrubland, and regosol soil. Occasionally frosts and hailstorms occur in the winter.

Species in study and material used

The species under study is the cósahui (Krameria erecta Willd), being a plant in the Sonoran desert. Clipper scissors, paper bags, markers and pelouze digital scale, model SP5, were used.

Sampling

For sampling, four study sites were selected, (50 m x 50 m. With an area of 2,500 m2 per quadrant) of summer pastures under grazing conditions (active). The collection of plant material was carried out at random, the phenological stage was not considered because there was a variation between the same times of evaluation; a considerable amount of plant matter (leaf, stems and flowers) was collected; they were mixed and divided into three samples. This same procedure was performed for each of the sites under study.

Dates of Collection

According to the weather conditions present in the state of Sonora, it was considered to carry out the proximal chemical analysis of the four seasons of the year (spring, summer, autumn and winter). The collection of plant material was carried out on the dates shown in table 1.

Chemical analysis

The nutritional content of Krameria erecta was carried out in the animal nutrition laboratory of the Department of Agriculture and Livestock of the University of Sonora, using the methods established by the AOAC (1995), which includes the moisture content (method 930.04), crude protein using the Kjeldah method (method 955.04), ashes (by calcination at 550 °C) (method 930.05), ether extract (method 962.09) and crude fiber (method 920.39). As regards the dry material, it was ground in a Willey mill with a mesh size of 1 mm; it was then dried at 55 °C for 48 hours to obtain the dry weight.

Statistical Analysis

The data obtained were analyzed with a completely randomized design, the quadrants and four seasons of the year (spring, summer, autumn and winter) were evaluated. With the data obtained, an analysis of variance was performed. For the comparison of means, the Tukey-Kramer mean test was used, with an alpha of 0.05%. These analyzes were carried out using the statistical package JMP 5.0.1 (^{JMP, 2002}).

RESULTS AND DISCUSSION

When evaluating the nutritional content of Krameria erecta, it was shown that there are significant differences with respect to the sampling time and between the sites in the percentage of ethereal extract, % of dry matter, % of humidity, % of ashes, % of phosphorus and % of calcium.

Regarding the percentage of protein, it is observed that they presented significant differences in the four seasons of the year and it was also shown; while in the rest of the sites evaluated no significant differences were shown, presenting crude protein values on average from 7.46 to 13.42 % throughout the year. The highest percentages of crude protein were in the summer season, this may be due to the fact that the protein increases its concentration when the plant is in water stress for prolonged times (Table 2). Due to their considerable protein levels, multipurpose nature, wide margin of adaptation and production capacity, the biomass of trees and shrubs can contribute to improving the quality of the animals' diet (^{García et al., 2009}).

^{Marshal et al. (2005)}, evaluated the raw protein of Krameria grayi Rose and Pintor, at four times of the year, showing for winter 10.97%, spring 10.83%, summer 8.55% and autumn 10.62%. These results differ in the four evaluation periods with those obtained in this study, since Krameria erecta presented higher values in the four periods evaluated.

They also differ with the results obtained by ^{Toyes-Vargas et al. (2013)}, who analyzed the raw protein content of 5 native forage species: huizache (Acacia farnesiana), mesquite (Propsopis glandulosa), palo fierro (Olneya tesota), palo verde (Cercidium floridum) and Vinorama (Acacia brandegeana); presented values of 14.68 to 22.74% crude protein. This difference between the results could be attributed to the fact that the species analyzed by ^{Toyes-Vargas et al. (2013)}, are fabaceae.

In the case of ethereal extract, statistically there are significant differences with (P <0.05). Between the sites and time of collection, the collection dates presented values of 1.8 to 2.4% of ethereal extract; see table 2. The percentage of dry matter presented significant differences between the sites and the time of collection, showing values from 71.2 to 87.3%. It is possible to mention that these results are related to protein content; in summer, the plants have a higher dry matter content and therefore less moisture (Table 2). The presence of rains presents important changes in the content of protein and dry matter, causing the decrease of these variables and increasing the % of humidity, as clearly shown in this study when obtaining values from 12.7 to 28.8% (Table 2).

It is worth mentioning that the results obtained regarding the percentage of dry matter in this study, differ from those of ^{Toyes-Vargas et al. (2013)}, who evaluated some species of native Huizache (Acacia farnesiana), mesquite (Propsopis glandulosa), palo fierro (Olneya tesota), palo verde (Cercidium floridum) and Vinorama (Acacia brandegeana); obtaining results from 92.53 to 96.38%.

Therefore, it can be mentioned that, due to lower water availability in the soil, the edaphic evapotranspiration of the plants was greater and had an impact on the humidity variations in the analyzed plant tissue ^{Ojeda et al. (2012)}. The chemical composition of the plant may vary, mainly depending on the environmental conditions (^{Gallego et al., 2014}).

The tree and shrub component involved in these systems have broad effects on the nutritional framework of herbivores (^{Carmona, 2007}); due to its considerable protein levels, multipurpose nature, wide margin of adaptation. Trees and shrubs can contribute improving the quality of the animals' diet. It is necessary to evaluate the chemical and nutritional composition of the most promising species in livestock ecosystems, in order to establish the main advantages and limitations in the use of each one for animal feed (^{García and Medina, 2006}; ^{García et al., 2009}).

Due to the chemical composition and nutritional value of its foliage, flower and fruits, and of high acceptability by animals; woody plants can be considered to have forage potential (^{Pizzani et al., 2006}; ^{Pinto-Ruiz et al., 2010}), and constitutes an important forage with different nutritional values, depending on the part of consumption and the time in that the natural protein bank is found during the year (^{Orskov, 2005}; ^{Hernández et al., 2008}).

It is worth mentioning that the percentage of ashes present in Krameria erecta, showed significant differences at the time of collection, but not between sites; except in the winter time. On site two they were different from the rest, from that same era. The ash values present were from 7.41 to 13.33%. In the ash content the results differ with those of ^{Toyes- Vargas et al., (2013)}, with Krameria erecta values being higher, with respect to huizache (Acacia farnesiana), mesquite (Propsopis glandulosa), palo fierro (Olneya tesota), palo verde (Cercidium floridum) and Vinorama (Acacia brandegeana).

In relation to the percentage of crude fiber (% FC), there were significant differences at the time of collection, showing averages of 23.78 to 32.82%; but there is no significant difference between the sites evaluated (table 3). The metabolic processes of plants are not related to the raw fiber content, as they do not intervene in them. Kurdish fiber is necessary to carry out the digestive processes, so the southern cósahui shows considerable values of raw fiber at the different times evaluated. On the other hand, when comparing these results with those of ^{Toyes-Vargas et al., (2013)}, they are similar in terms of the percentage of crude fiber, with respect to the huizache (Acacia farnesiana), mesquite (Propsopis glandulosa) and Vinorama (Acacia brandegeana) and the percentage of raw protein of Krameria erecta differs with those of palo fierro (Olneya tesota) and palo verde (Cercidium floridum), presenting higher values Krameria erecta.

Calcium presented significant differences in spring time sites. The seasons of summer, autumn and winter did not show significant differences, except at site three of the winter season, with respect to the rest of the sites of that time. Therefore, this element does show variation in the analyzes in the spring season, this being a stationary element in the soil (table 3); but the variation of this one in the plants, can be due to the fact that calcium canvary its presence in soils that present erosion problems; and considering the latter, it is possible to attribute this variation to the lack of vegetation in the study sites.

With respect to the percentage of phosphorus present in Krameria erecta, it is observed that there is a significant difference (P> 0.05), between the times of collection (summer, autumn, winter and spring); showing no significant differences (P> 0.05), between the winter-spring collection seasons and their respective collection sites; when values of 0.05 to 0.09% are presented (table 3). These values can be attributed that the phosphorus is not very mobile in the soil, but it is movable in the plant.

Despite the drastic changes that occur in this region during the four seasons (seasons) of the year, Krameria erecta shows good nutritional potential, as it does not have such strong variations in its bromatological composition in terms of raw fiber, calcium, ethereal extract dry matter and phosphorus. For this reason, it is important to know the food content and nutritional value of the native individual species (^{Guerrero et al., 2010}). The use of natural resources in a rational and sustainable manner is a viable option to obtain benefits in agricultural activities (^{Quansah and Makkar, 2012}).

Fodder trees and shrubs are species adapted to the soil conditions and climate of the region, which ensures their survival, persistence and growth from moderate to relatively rapid with high probability; It improves the diet of the animal and reduces the use of concentrates in livestock farms, providing favorable conditions for the increase of the productive response of the animals (De Andrade et al., 2008; ^{Rodríguez and Roncallo, 2013}; ^{Sosa et al., 2004}; ^{García and Medina, 2006}; ^{Petit et al., 2009}). Therefore, the integration of trees in the pastures presents an option to improve the productivity and sustainability of livestock (^{Ortega, 2013}).

It is important to note that to discuss the results obtained. Little information is available on the nutritional content of other species in the Krameracea family. More research should be done to continue evaluating the nutritional content of other species not yet studied, which are of great importance to animals; since they cover a large part of their nutritional needs. The above is indispensable for the establishment of strategies for sustainable management of silvopastoral systems; however, livestock activity is carried out under production systems that are not friendly to the environment. Production must be sustainable in biological and economic terms for agricultural production (^{Korbut et al., 2009}; ^{Oliva et al., 2015}; ^{Oliva et al., 2018}).

CONCLUSIONS

The chemical composition of southern cósahui (Krameria erecta) showed a higher nutrient content in summer, except in ethereal extract. The content of the crude protein percentage is almost double in summer than in winter. The statistical analysis between seasons of the year (time) of sampling, indicates that there are significant differences. In the autumn season Krameria erecta provides more percent fat and carbohydrates, as energizers for herbivores.