INTRODUCTION

Trees and fodder shrubs grow naturally in crops, pastures, acahuales and other sites; they are usually used to obtain shade, wood or firewood; however, they can also serve as fodder in cattle feed (^{Ku et al., 1999}). Their presence could become a very profitable option and even contribute to the conservation and restoration of biodiversity (deforestation and soil degradation), which in recent years has been lost rapidly in areas formerly rich in natural resources (^{Calle et al. ., 2011}).

^{Galeano et al. (2013)} before this situation, mention that the foliage of tree species can be a good alternative for food sustainability, because they have a great potential as forage (Gliricidia sepium, Paramentiera acuelata, Leucaena leucocephala, Guazuma ulmifolia, Morus alba) ; that is, a high protein content compared with grasses and biomass yield (^{Mtengeti and Mhelela, 2006}). Most of these species have leaves that serve as food for cattle, horses, sheep and goats. Some also bear fruit, such as pods that can be used in animal feed; emphasizing that both foliage and fruits can have very good nutritional characteristics (^{Pinto et al., 2010}).

^{González and Cáceres (2010)}, reported that the management and use of fodder trees and shrubs is motivated, among other aspects, by the adaptation of species to regions with prolonged drought, and low supply of grasses. Many species are edible by animals and are naturally available in paddocks, offering: 1) foliage or fruits of reasonable quality, 2) low cost of food production, 3) reduction of production costs due to the decrease in the use of chemical products for weed control, 4) local knowledge of producers about plants consumed in pasture and 5) use of biodiversity and are also a source of protein, energy, minerals and vitamins.

The adaptation of species to regions in times of prolonged drought and low supply of grasses, make them an alternative of edible species for animals, in addition to offer reduction of production costs due to the decrease in the use of chemical products for the weed control, local knowledge of producers on trees consumed in pasture (^{Foild et al., 1999}).

Similarly, guidelines could be given for the development of sustainable production systems that do not threaten the ecological balance of these areas and that could even improve animal behavior (weight gain, milk production, feed conversion, etc.), without having to depend on other external agricultural inputs. Therefore, food alternatives such as silvopastoral are required to face the dry season, and the association of shrubs with grass for animal production, friendly with natural resources and biodiversity, is appropriate (^{Aguirre, 2013}).

The use of these forage species is done in the form of grazing, allowing browsing of the animals or in cutting and carrying, which is less common (^{Saabreda and Rodríguez, 2018}). It is important for the selection of species to take into account the following criteria: 1) adaptation to the soil and climate conditions of the farm, 2) good forage production, 3) having a good palatability (pleasant to the taste of the animal), 4) have a good nutritional value, 5) tolerate frequent pruning or grazing, 6) good regrowth and growth capacity and 7) not contain substances toxic to animals (^{González et al., 2006}).

Among the different alternatives available to reduce the environmental deterioration produced by the growth of extensive traditional livestock, the implementation of agroforestry practices (silvopastoralism) has been implemented, which promotes the integration of trees and shrubs with animal production (^{Sosa et al. ., 2004}). Likewise, guidelines could be given for the development of sustainable production systems that do not conflict with the ecological balance of these areas, and that could even improve animal behavior (weight gain, milk production, feed conversion, etc.), without having to depend on other external agricultural inputs (^{Gascón et al., 2004}). Therefore, this project aims to know the main species of trees and fodder shrubs that are consumed by bovines in northern Veracruz, as well as identify their different uses.

Faced with this problem, it is intended in Tamalín municipality, Veracruz, to produce and maintain the balance of the ecosystem, rescuing it through agroforestry. This system offers great diversity, in the first place it offers the following environmental benefits: it favors the biological diversity of flora and fauna, the primary producer of food for humans, animals and the soil, it is the only one capable of harnessing primary energy, it is a great producer of raw materials, gives shelter to other living beings, animals and plants, light regulator to favor the growth of crops (coffee), cleaner of the planet capturing CO₂, regulator of the hydrological cycle of water, provides comfort to different species, favors the nutrient recycling, primary producer of chemical substances for the production of medicines and high sprout capacity (^{Sosa et al., 2004}).

It is important that in this municipality that the agricultural production units are more profitable, using for it the agroforestry systems, silvopastoral, agroforetry, forestry fruit-pastures. ^{Cárdenas et al. (2011)}, mention that all these systems are focused towards the use of production techniques more harmonious with the biophysical and socioeconomic realities of the countries of the tropics. Trees are part of a wide variety of agricultural systems, in which they perform a large and large number of functions in the ecosystem; as, for example, protect the environment, and produce vital, economic and social resources. In addition, they contribute to reducing soil losses, protecting and providing lower vegetation cover; which reduces erosion and improves the physical conditions of the same, such as structure, porosity and water retention capacity. Among the diverse benefits that the arboreal wealth offers us, its moderating action in the macro and microclimate stands out, the stabilization and improvement of the soil fertility, lodging of the wild fauna and control of pests and diseases (^{Amparo et al., 2018}).

MATERIAL AND METHODS

The work was carried out in Palmarillo town, located in Tamalín municipality,in the State of Veracruz, Mexico; located between the coordinates 21 ° 20 'North Latitude and 97 ° 49' West Longitude, at an altitude of 140 m a.s.l. This work was carried out with the following activities:

RESULTS AND DISCUSSION

The information obtained from the surveys applied to the livestock producers of the Palmarillo community, belonging to Tamalín municipality, located north of Veracruz, Mexico; they show the presence of trees and shrubs with forage potential, allowing the identification of eight species that are particularly desirable and with high levels of digestibility (Table 1). This served to identify species that normally had another use, as well as to extend the usefulness of those that were used for other purposes. It is important to mention that with the support of this survey information was gathered that in this municipality, the selection of herbaceous plants predominates, and during the drought the bushes constitute the main component of the animal diet. Likewise, the fraction of the plant that is consumed by the animals is also different, observing in some cases the consumption is of leaves, stems and fruits.

In Table 1, trees and fodder shrubs that have been used for thousands of years for various purposes are identified. Some of the advantages over the grasses consumed by bovines are the following: an adequate nutrimental contribution (12-19% of crude protein), they have a permanent production especially in dry season, the consumption by bovines is adequate as to expect changes in their productive parameters (milk and meat), to show tolerance to pruning and to have a regrowth vigorous enough to obtain significant levels of edible biomass production per unit area (^{González and Cáceres, 2010}). Also, the use of tree species in animal feed, promotes a favorable environment in the rumen that induces better fermentation and digestion of low quality forages (^{Gobbi and Casasola, 2003})

Finding species that have important characteristics that make them desirable to be established and used, as a source of protein and vegetable energy, improve the animal diet, providing a variety of foods, fodder, fruits and leaves, which allow the animal to vary its diet and increase its level of production (^{Das et al., 2016}).

With the application of the survey it was possible to determine the use that the producers give to the fodder trees and shrubs, which in their opinion were the most important based on the percentage of use detected in the surveys and the value assigned by the producer to each species, based on the observation made by the producer. Regarding the percentage of utilization commented by the respondents, the knowledge of the producers and their interest in the trees and fodder shrubs are appreciated (Table 2), which represent a part of their sustenance, use of the herbalist as treatment of some disease, obtaining firewood, as well as the raw material for their livestock.

These results obtained through the survey, allow to identify some species with multiple uses, being able to cover the needs of the producer in terms of forest and forage products. The evaluations carried out can be used to constitute the knowledge base that leads to the alternative development of the improvement of the current systems or the introduction of new practices in the production units in the regions under study. Also to promote the conservation of autochthonous species, since there will always be a potential danger of extinction of these species, due to a possible overuse (^{Delgado et al., 2014}).

In relation to the most important criteria related to the animal and to the fodder trees and shrubs that were suggested by the surveyed producers, they are observed in Table 3, which presents the most important criteria related to the animal and the forage species that were suggested by the producers surveyed, and that define the forage criteria (trees and fodder shrubs) of the production system. The most relevant criterion in terms of those related by the animal, is the maintenance of body condition (85%) and the increase in milk production (80%).

This study differs from that presented by ^{Pinto et al. (2010)}, revealing that the most relevant criterion in the three regions of Chiapas state was related to the knowledge that tree species are browsed by the animal (78%), followed by the amount of leaf biomass that they possess. said species (75%).

Regarding the second criterion related to the knowledge of tree species (Table 4), the resistance to drought and a high nutritional value of the species Morus alba (92%), Leucaena leucocephala (90%) and Guazuma ulmifolia ( 85%); demonstrating that most of the characteristics of the trees and forage shrubs as indicators of their forage value, were based on the physical attributes, and that they are easily observed by the surveyed producers; which indicates a high degree of empiricism (100%), in local knowledge.

As for the species studied (Table 5), they showed acceptable nutritional contents; highlighting the Crude Protein (PC), being much higher than those of tropical pastures, and in several cases, also superior to that of commercial concentrates; due to its high protein quality, the following stand out: Morus alba (20.22%), Guazuma Ulmifolia (16.72%), Leucaena Leucocephala (14.66%), Gliricidia sepium (16.28%).

Unfortunately, these trees have been felled to induce grasses for the production of forage; the producers surveyed mentioned that fodder trees and shrubs were born alone, that is, naturally, since they have never been planted (^{Foidl et al., 1999}). It is necessary to mention that to maintain the productivity of an ecosystem it is necessary to maintain a balance between: soil-nutrients-human-plants (crops), sunlight and water; and that the synergism of these produces the production and perpetuity of ecosystems (^{Delgado et al., 2014}).

^{Rocha et al. (2013)} agreed that most of the shrubs and forage trees in the tropics show strong variations in the levels of crude protein and digestible energy, which is related to the different ages of each fraction of the shrubs and fodder trees. ^{Gascón et al. (2004)} indicated that variations in the nutritional content of the trees and shrubs analyzed could be attributed to a set of variables, such as: characteristics of the species, site of growth and soil type, age of the tree and type of component (fruit or foliage).

^{Galeano et al. (2013)}, showed that the chemical composition of Morus alba and its nutritional quality are distinctive features of the species. It is a generalized consensus that the mulberry presents an excellent nutritional quality, which has been documented for decades, in addition the nutritional value of Morus alba has been exhaustively studied all over the world (^{Calle et al., 2011}). From the point of view of the variations in the chemical composition and the nutritional value, in studies carried out with this forage shrub, it is reported that the greatest fluctuation occurs with the factor: cut frequency, fertilization factors, variety and time that they have a substantial influence on the composition and nutritive quality of the biomass (^{Velázquez and Mora, 2008}).

^{Murgueitio and Ibrahim (2007)}, reported that the variation in nutritional content could be attributed to a set of variables, such as: the characteristics of the species, growth site, soil type, age of the tree and fodder shrub, as well as as the type of component (leaf, fruit, stem, and forage). ^{Holguín et al. (2008)}, conducted a study with calves in the growth stage, demonstrating that, of 84 species consumed, at least once a day, nine of them represented 54% of the total bites of the animals; among which stand out (Leucaena leucocephala, Vachellia farnesiana, Morus alba, Gliricidia sepium, Guazuma ulmifolia).

^{Salas et al. (2011)} reported that geographical variability turns out to be an important factor for established forage trees and shrubs that have a wide range of distribution, to the extent that, in addition to their natural dispersion, they have suffered a wide artificial dispersion due to the action of the man; with this, in a new ecological niche, plants begin a new evolutionary process, in which they create adaptation strategies to environmental variations (^{Cárdenas et al., 2011}).

This research coincides with that carried out by ^{Sosa et al. (2004)}, observed that the selection of the forage species is influenced by the rains that determine changes in the type of vegetation. ^{Salem et al. (2007)}, indicate that in the rainy months the selection of herbaceous plants predominates and during the drought the trees and fodder shrubs; which are the main component of the diet of bovines, having higher consumption Morus alba and Leucaena leucocephala.

CONCLUSION

The species identified in the municipality of Tamalin, Veracruz, Mexico, were Chaca (Bursera simaruba), Palo de sol (Gliricidia sepium), Chote (Paramentiera aculeata), Ramon (brosimum alicastrum), Palo Rosa (Tabebuia rosea), Leucaena (Leucaena leucocephala), Guasima (Morus alba) and Morera (Guazuma ulmifolia); which proved to be naturally available in the production units. Resistance to drought, ease of propagation, nutritive value and regrowth are reported from each species. The nutritional content of the trees in animal feed varies from 7.9 to 20.22% of P.C. and from 2.55 to 3.25 of E.M.