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INTRODUCTION
Livestock in Mexico is an economic activity with a strong social relationship, since 80 % of the income of rural production units are due to agriculture and livestock, with limited economic income that induces poverty (SAGARPA-FAO 2012). Livestock is an activity associated with problems of deforestation, erosion, biodiversity loss, pasture degradation and pollution with greenhouse gases (GHG) related to climate change (Nahed et al. 2014). All this coupled with a population demanding food, characterized by a social dichotomy where the majority of the population is located in the extreme poverty stratum in contrast to the concentration of wealth in a few (Esquivel 2015).
In the case of Mexico, this socioeconomic panorama is not exempt from its association with a context of environmental problems (SEMARNAT 2012) where 42% of the national surface could be affected by water erosion with 17 states with damage in more than 50 % of its territory, among them: Guerrero (79.30 %), Puebla (76.60 %), Morelos (75.20 %), Oaxaca (74.60 %) and the State of Mexico (73.70 %). Also the mountain regions of Sierras Madre Oriental, Occidental and del Sur, as well as vast regions of Chiapas and the entities of the center of the country, would be at risk of presenting high and very high soil loss due to water erosion. With respect to potential wind erosion, it was estimated that 89 % of the national territory would be at risk of being affected. Practically 100 % of the territory of Aguascalientes, Baja California, Baja California Sur, Sonora, Durango and Zacatecas, would have high and very high potential wind erosion, which agrees with the types of typical climates and vegetation in the arid and semi- arid zones of the country. In chemical degradation, the decrease of soil fertility predominates (92.70 % of national surface) and in physical degradation, compaction covers 68.20 % of the national surface. All of them are alarming indicators, especially due to their impact on agricultural surface, which compromises the sustainable development of the country (FAO 2016).
In this context, different authors including Nahed et al. (2014) and García-Barrios and González- Espinosa (2017) stated the importance of resilience of agricultural systems where their socio-environmental conditions are considered, and the options based on silvopastoral models (SSP) are a friendly strategy with the environment, socially fair, economically viable and with resilience characteristics. In particular for family-scale producers, it should be noted that resilience is defined, from the social field, as the recovery and improvement ability of the initial condition when an individual and its community are affected by adverse factors that threaten their own survival and/or balance. However, in the case of biological processes, which are non-linear dynamics, the processes through which ecosystems sustain themselves and endure disturbances are considered. Therefore, resilience is considered as the ability to maintain during time and space by taking advantage of continuous learning, transformation, renewal and evolution.
In this sense, the use of natural resources (Lara et al. 2016) and/or agricultural or agroindustrial wastes in an area or region that may be contaminants (Del Viento and Palma 2015), but integrated into the diet of ruminants, become rational elements of nutritional complementation, especially valuable in drought conditions.
Therefore, the purpose of this paper is to propose the integration of tree species associated with agricultural and agroindustrial wastes in the feeding of ruminants for the development of resilient systems in the dry tropics of Colima, Mexico.
CLIMATE CHANGE AND TROPICAL CATTLE REARING
The challenge of livestock in a tropical environment in the climate change scenario is the identification of adaptation and/or mitigation mechanisms. In the case of adaptation, it is defined as those initiatives and measures that reduce vulnerability of producers and their systems, before the actual or expected effects of this change.
One of the challenges for adaptation is the use of ecological and social resources and processes that allow its persistence, by timely cushioning adverse disturbances, prudently reorganizing and modifying when internal and external structural changes occur.
Under current conditions, agricultural and livestock systems face frequent and unpredictable disturbances, caused by factors such as adverse effects (direct or indirect), as a consequence of climate change and economic, financial and energy crises, among others.
The intergovernmental panel on climate change (IPCC 2014) pointed out that these effects can be random, irregular and, sometimes, surprising. They respond to a dynamic of short or medium term, and that, unfortunately, will continue to increase. Depending on their nature, they will continue to affect the systems at different levels of their organizational scale, from the level of biological function of an individual, up to the levels of organization of socioeconomic structures.
Disturbances in a system occur at different scales and can influence on:
its own general functioning or trajectory;
the functions and dynamics of any of its components independently and
the interrelationships among its components and its processes.
These effects are considered or classified as static (punctual), transitory or, on the contrary, dynamic and persistent in time and space.
Therefore, the vulnerability of these systems will depend on the magnitude and nature of risks of internal and external disturbances, and their adaptation ability and that of their components to be resilient, through the promotion of the natural and strategic combination of mechanisms of regulation or specific intervention actions.
Therefore, resilience ability considers the combination of individual or collective reserves of natural and human capital (Altieri and Nicholls 2009), which include qualities such as traditional knowledge, skills, abilities and social organization level in the productive systems.
Consequently, the design of resilient livestock systems considers:
Integration of local resources,
incorporation of ancestral knowledge associated with the current one,
decrease of negative externalities, and
search for har mony through human relations with nature.
Therefore, for the development of resilient systems (Reinjtes et al. 1992), the following elements for its development are considered:
Increase of biomass recycling, availability optimization and balanced flow of nutrients
Assurance of favorable soil conditions for plants growth, particularly, through the management of organic matter and increase of soil biotic activity
Increase of system efficiency due to the flow of solar radiation, air and water through microclimate management, harvesting with water and soil management through increase of coverage
Specific and genetic diversification of agroecosystems in time and space
Increase of biological interactions and synergies among biodiversity components by promoting key ecological processes and services of the system
CATTLE REARING SYSTEMS IN THE DRY TROPICS
One of the tools that allows the increase of environmental services is agroforestry (Shibu 2009), effects that have different scale of impact, with benefits at ranch, landscape or region level and globally.
In this case, these principles are addressed at the producer and productive agricultural unit level, without forgetting that this impact will have an effect on other levels. In this regard, it is considered that, at the level of this scale, the following principles can be developed:
Search for low use of external inputs, which, at the same time, implies the knowledge and promotion of the use of local resources
Likewise, improvement of animal feeding through the use of this local resources, in particular of tree and /or shrub resources and of agricultural and agroindustrial wastes
Promotion of a clean production
Development of an organic cattle rearing
Proposal of a microenvironment for livestock, grass, soil, water, as well as microflora and microfauna
It is intended to avoid grass degradation
Prevent erosion
The increase of trees with different purposes in cattle rearing systems
For the above described, elements that dynamizes livestock and its adaptation ability or modification over time are: versatility, high level of diversification and complementarity with the other activities, which allow the system to endure climatic and economic changes as a result of their lower dependence on individual productive factors, as well as their low investment level.
Livestock promotes direct economic income, benefits environmental sustainability through the use of available resources. Therefore, livestock is an asset that favors the reduction of vulnerability of exploitation and poverty, through a strategy of minimum cost, with levels of efficiency and technological innovation according to their condition of minimum investment, which must be analyzed and evaluated to achieve the desired impact on farms.
However, one of the characteristics of dry tropics is its marked seasonality, a phenomenon that limits quantity and quality of ruminant feeding, with production restrictions that induce low productive indicators as shown by multiple studies in the tropical area of Colima, Mexico (Cervantes 1988, Palma et al. 1993, Esperón 2000 and González 2003), that means that there is a stagnation of tropical cattle rearing, with slow changes in family scale producers, in the neoliberal economic context.
This phenomenon can be reversed through the synchronization of available local inputs (residues of reject banana, agroindustrial residues of lemon, coffee, mango, coconut, and papaya). At that critical time, they also described some fruits of tree species that would potentiate tropical bovine cattle rearing (Palma and González-Rebeles 2018), such as Parmentiera edulis, Enterolobium ciclocarpum, Guazuma ulmifolia, Caesalpinia coriaria, Senna atomaria, Vachelia pennatula, Crecentia alata and Jacaratia mexicana and that would be an important complement for the use of agricultural wastes such as the tip of cane (Lara 2015 and Ramírez 2017).
Therefore, this document proposes that tropical cattle farming is resilient, due to the ability of the system to absorb disturbances, maintaining its functions fundamentally without major changes, as well as for renewal and reorganization. It depends on natural resources (soil, water, and biodiversity) and on the level of knowledge, learning ability and management of human groups and their institutions (Astier et al. 2012).
DISCIPLINARY, MULTIDISCIPLINARY AND TRANSDISCIPLINARY VISION INTROPICAL LIVESTOCK
From discipline, our study object is ruminant nutrition, maybe milk or meat production in tropical bovine systems. However, through transdisciplinarity, it interacts with health, reproduction, genetics, management, economy, that is, animal husbandry in general. But because of the complexity of the system, the interaction of ecological, social and economic processes is necessary and indissoluble.
Above all, due to the fact of adding ecological elements like trees in production systems after their elimination, where, despite producers recognize their multiple functions and favorable interactions (Palma and Flores 1997), their inclusion for livestock purposes has limitations (García-Barrios and González- Espinosa 2017).
On the other hand, when a transdisciplinarity approach is applied, the participation of farmers in decision-making, their relationships with the environment and the social dynamics that occur in these territories was recognized, originating heterogeneous results in silvopastoral systems (SPS). Out of the outstanding results in tropical cattle rearing, the establishment of grazing or forages species such as Cenchrus purpureum cv. Cuba CT-115 and the protein banks with Gliricidia sepium (García-Barrios and González-Espinosa, 2017).
TREES, AGRICULTURAL AND AGRO-INDUSTRIAL BY-PRODUCTS (AAB)
In the last two decades, different studies characterize tree species for forage purposes in Mexico, as in the case of Colima (Palma 2005, Román and Palma 2007 and Román et al. 2016), Chiapas (Pinto et al. 2004, 2010), Michoacán (González-Gómez et al. 2006), Veracruz (Bautista-Tolentino et al. 2011) and Yucatán (Ku-Vera et al. 1999), to mention a few examples, where there is a potential beyond the use of Leucaena leucocephala as the most studied and used species in a productive way.
Therefore, biodiversity is a characteristic of Mexico and within it, its arboreal richness allows the development of livestock agroforestry with multiple and innovative options (Palma et al. 2011). This study shows the diversity of systems and tree species in livestock systems, related to the diversity of agro-ecological regions and, in particular, to the tropical area.
In this context, there are multiple examples that have potential to be explored as detonating elements of silvopastoral systems, as in the case of Tithonia diversifolia (Mejía-Díaz et al. 2017 and Ruiz et al. 2018), who study their agronomic characteristics as nutritional feeding and their impact on animal production that adapt to climate change. In this regard, the use of Ricinus communis leaf has been proposed as an alternative forage in the feeding of ruminants, a species with great plasticity and high adaptation to different altitudinal levels, as well as tolerance to adverse conditions of soil quality and water requirements (Del Viento et al. 2014). Table 1 shows the nutritional values of crude protein, estimation of the energy value and in situ digestibility of this species (Ramírez et al. 2017), compared to alfalfa and sugarcane tip.
ASPECTS OF THE REVIEW OF TECHNICAL OPTIONS FOR THE REDUCTION OF GAS EMISSIONS OTHER THAN CO2
In the development of scenarios for bovine meat production in Mexico for cow-calf and for the double purpose system, it is proposed to improve the productive performance in terms of the percentage of weaning as well as its weight and age, economic tools that detonate these systems (Palma 2014), also as a strategy of adaptation and mitigation to climate change.
In this regard, FAO showed through a review on the subject, that, from the perspective of enteric fermentation, manure management and animal husbandry, the potential of available strategies to mitigate greenhouse gases (GHG) other than CO2, such as the use of food additives and their reproductive management (Gerber et al. 2013).
Out of the strategies indicated by Gerber et al. (2013), those that, from a silvopastoral or RAA management approach, could be implemented in our conditions and with applicability in all the productive regions of the world, such as the dietary protein balance, the inclusion of dietary lipids, the inclusion of concentrates based on their availability and their market prices, grazing management, supplementation or strategic supplementation of low quality feed and precision feeding. This document emphasizes achievements for temperate regions (table 2).
On the other hand, these same authors stated different strategies from animal handling point of view, in order to achieve mitigation of greenhouse gases other than CO2 (Gerber et al. 2013). Selected categories were based on potential impacts in Mexico and, particularly, their possibility of application with silvopastoral systems and the use of RAA (table 3)
Table 2 Feed additives and feeding strategies that offer mitigation possibilities of greenhouse gases other than CO2 (Gerber et al. 2013)
1 Mitigation strategies in this table are applicable to all ruminants
2 High = mitigation effect ≥ 30 percent; Medium = mitigation effect from 10 to 30 percent; Low = mitigation effect ≤ 10 percent. Mitigation effects refer to change percentage regarding a “standard practice”, that is, a control study used for comparing and based on the combination of research data and the judgment of the authors of this study.
3 Efficiency is determined on the basis of: potential of GHG mitigation, effect of food intake (the non-negative effect is beneficial) and effect on animal productivity (the non-negative effect or improvement is beneficial).
4 Based on data of EPA, FDS, or expert opinion.
5 Based on available research or on the lack of sufficient research
6 Regions: All = all regions; EU = Europe, AS = Asia, AF = Africa, NA = North America; SA = South America; OC = Oceania.
7 Toxic effects when CP is marginal or inadequate in the diet or when condensed tannins are astringents and in high concentrations. However, with adequate CP in the food, some condensed tannins may have a wide range of beneficial effects.
8 Lipids are generally efficient in reducing the production of enteric CH4. They are recommended when their use is economically viable (the oil-rich byproducts of biofuel industry, for example). Its potential negative effect on feed intake, fiber digestibility, rumen function, milk fat content and overall animal productivity should be considered. The recommended inclusion rate in ruminant diets is 6 to 7 percent (total fat) of DM of the diet. In the absence of mechanisms that encourage the reduction of enteric CH4 emissions, economic feasibility of supplementing diets with edible lipids is questionable.
9 Although it is recommended (direct reduction of enteric CH4 emissions, or indirect, through increased animal production), the application of this mitigation practice will depend to a large extent on the availability of feed.
10 Not very consistent results, but recommended based on the fact that an improvement in pasture quality should reduce CH4 emissions per unit of food intake and of animal product.
11 Even if the direct mitigation effect of CH4 is uncertain, precision/balanced feeding and accurate food analysis may increase animal productivity and feed efficiency and will improve farm profitability (thus having an effect of indirect mitigation of CH4 emissions and enteric N2O and manure).
Table 3 Strategies of animals management that offer opportunities of mitigation of greenhouse effect gases other than CO2 (Gerber et al. 2013)
?Indicates uncertainty due to limited research or lack of data, inconsistent or variable results, or absence or insufficiency of data on the persistence of the effect
1 BL = milk cattle; BC = beef cattle (bovines include Bos taurus and Bos indicus); CE = pigs; AS = all speciesm
2 High = mitigation effect ≥ 30 percent; Medium = mitigation effect of 10 to 30 percent; Low = mitigation effect≤ 10 percent. Mitigation effects refer to change percentage regarding a "standard practice," that is, a control study used for comparison and is based on the combination of research data and the judgment of the authors of this document.
3Determined based on: GHG mitigation potential and/or productivity effect (non-negative effect or improvement is beneficial)
4Based on available research or on lack of sufficient research
5 Regions: All = all regions; EU = Europe, AS = Asia, AF = Africa, NA = North America; SA = South America; OC = Oceania.
6 Productivity increase will have a powerful effect on the mitigation of GHG emissions, but the level of effect will depend on several factors (baseline productivity, type of animal, type of production, quality and availability of food, genetic constitution of the herd, etc.).
7 Only meat animals
ADAPTATION AND MITIGATION TO CLIMATE CHANGE FOR A RESILIENT TROPICAL LIVESTOCK IN MEXICO THROUGH SILVOPASTORAL SYSTEMS (SPS)
Adaptation is defined as the ability of systems to reproduce themselves for a reasonable time. They have the possibility of being properly modified to maintain their functionality, when the scenario is altered.
Therefore, adaptation considers all those initiatives and measures used to reduce vulnerability of society and susceptibility of natural systems in front of the real or expected effects of modification of such scenarios.
In response to the negative effects associated with the activities of bovine cattle grazing, the promotion of an environmentally sustainable reconversion is a priority, as a different production strategy that limits the transformation of ecosystems and generates or maintains environmental services.
This strategy implies the recognition of ecosystemic services that can be obtained through diversification of domestic animals in production, combination of feeding through the use of native and cultivated natural or exotic plant species, control of stocking rate according to the potential of ecosystems, mitigation of negative impacts on soils, as well as integration with other local and regional production systems, just for mentioning some aspects (Anta and Carabias 2008 and Balvanera and Cotler 2009).
The SPS and the use of biodiversity is an alternative proposal to conventional production of single-crops where different wild species survive in landscapes for conventional production that may be included in SPS, which allows the conservation of basic characteristics of structure and function of this agroecosystems with a consequent higher proportion of environmental services (Primak et al. 2001).
One of the most recent approaches with greater success is agroforestry with its respective variants and combinations of systems (for example, agroforestal, silvopastoral and agrosilvopastoral systems). These systems combine agricultural polycultures, forestry use and cattle management with approaches that promote higher structural complexity in paddocks through life fences, alley pastures, tree maintenance in paddocks, protein and energy banks (management of plots of trees, shrubs and forage legumes), secondary plant grazing and garden weeds, combination of groups of domestic herbivorous species in grazing, among other management techniques. These systems go from simple grazing of secondary vegetation (mountain grazing or grasslands), grazing in forestry plantations, up to system of high density with legumes and improved grasses, where tree richness is an essential element in the development of these systems, as it was reported by Palma et al. (2011) and by different species that can be used in the design of these systems (Palma and González-Rebeles 2018).
In the case of silvopastoral systems (SPS) as considered as plastic systems, due to their ability of modifying their structure, with adjustments to new goals. Plasticity is defined as the ability of adopting and changing shapes. In this sense, the SPS respond to current changes and to limitations of the environment, with high resilient ability as it was stated by Nahed et al. (2014), being an effort of humans for imitating nature.
In addition, SPS provide different strategies that allow mitigation of GHG through several mechanisms that combine design, density and use of biodiversity, among other factors that generate favorable impact on the environment. In this respect, table 4 shows different positive effects generated in productive systems, through implementation of silvopastoral systems in economic, social and environmental aspects in tropical areas (Palma et al. 2000, Ávila-Foucat and Rebollo-Fernández 2014 and González 2013, 2016).
The SPS in Mexico have an important function in the proposals of adaptation and mitigation to climate change, as, for instance, through high density sowing, which increases carbon fixation (Anguiano et al. 2013), nutrient recycling (Anguiano 2012), encouraging of edaphic fauna (Palma y Anguiano 2015), as well as the use of foliage and fruits with antimethanogenic activity (Ku-Vera et al. 2016), to increase digestibility of rations (Román et al. 2008) and in the generation of better animal welfare (Galindo et al. 2013, Améndola et al. 2016, 2018 and Mancera et al. 2018).
CARBON SEQUESTRATION
Information on C sequestration in SPS in Mexico, demonstrated by Anguiano et al. (2013), in a high density silvopastoral system of Leucaena leucocephala associated to coconut trees and Pennisetum purpureum cv. Cuba CT 115, showed levels of 101.19, 109.73, 122.00 and 128.62 t C+ha-1year-1 for systems with 0, 40, 60 and 80 thousand plants of leucaena ha-1, respectively where tree component, in different studied treatments, provided from 85 up to 98 % of fixed C+. Previous results were lower to those described in a deciduous forest in Huatusco, Veracruz, México, where 268.38 t C+ha-1 were obtained in the aerial biomass. These values may be attributed to forest components, plus the dasometric component of trees (Torres-Rivera et al. 2011). On the other hand, these same authors indicated values of 2.86 and 1.78 t C+ha-1 for the silvopastoral system with low density of tree component and conventional grazing, respectively. In addition, this study deals with C+ within the litter and soil. Solorio et al. (2011), in the area of Michoacán with traditional systems of star grass (C. plectostachyus)in monoculture, demonstrated values of 120 t C+ha-1, compared to 220 t C+ha-1in intensive silvopastoral system (L. leucocephala/P. maximum).
Also, Callo-Concha et al. (2004), estimated the accumulation of carbon in the aerial biomass of some agroforestry systems (AFS) of Veracruz, Mexico, during a production cycle. The systems used were: 1) citrus associated with banana; 2) citrus associated with coffee; 3) citrus associated with coffee and banana; 4) citrus with sheep grazing; 5) citrus associated with cover crops and 6) monoculture pasture. Results suggest that citrus fruits contribute between 65 and 8 % of tree carbon. Likewise, the highest contribution of total carbon is generated by tree biomass. In four out of the five evaluated AFS, their contribution varies between 95.7 and 97.8 %. The system based on citrus and Pelibuey sheep had the highest carbon accumulation with 63.4 to 94.7 t • ha-1 and the lowest was pasture with 1.4 to 2.1 t • ha-1.
In a recent review of Mexican authors on carbon fixation in the southeast of our country (Alayón et al. 2016), several baseline studies are compiled indicating that the highest value is obtained in systems with trees scattered in paddocks (88.89 Mg C ha-1), followed by live fence systems (87.5 Mg C ha-1) and finally in monoculture pastures (60.62 Mg C ha-1). The use of live fences with Gliricidia sepium had a carbon storage in the soil of 20.44 Mg C ha-1 year-1, compared to 19.22 Mg C ha-1 year-1 of pastures in single crops of extensive livestock.
ENTERIC METHANE MITIGATION
In a recent review on the state of the art of enteric methane emission for Latin America, Benaouda et al. (2017) noted that, in the case of Mexico, the estimation of emission factors and inventories are limited and recent.
Studies conducted by Castelán et al. (2014) and Ku-Vera et al. (2016) are pioneers in Mexico regarding quantification of methane gas in respiratory chambers, and the second authors use forage and tropical fruits and, in the first case, they work with foliage, mostly from temperate zones, besides taking charge of the inventory of greenhouse gases for ruminants in Mexico.
Also, Solorio et al. (2011) reported decreased of methane emission by comparing traditional star grass systems (C. plectostachyus) in monoculture with CH4 emission values (85 kg animal-1 year-1) compared with 68 in intensive silvopastoral system (L. leucocephala/P. maximum).
Essentially, the enteric methane mitigation approach focuses on identifying tree foliage or fruits with secondary metabolites, whether rich in tannins in particular condensates or in saponins, a phenomenon also observed in Mexico (Piñeiro-Vázquez et al. 2015 and Ku-Vera et al. 2016).
ANIMAL WELFARE IN SILVOPASTORAL SYSTEMS
The study of animal welfare associated to silvopastoral systems is recent, with favorable aspects in the performance for animals and, in this sense, it was observed that dermal temperature of livestock associated with silvopastoral systems is 4 °C lower compared to the cattle in monocultures (Galindo et al. 2013). It is important to consider that high temperatures increase water intake, loss of energy and modify feeding times in monoculture paddocks compared to SPS (Améndola 2013 and Améndola et al. 2016).
Likewise, effects such as anxiety and fear in animals, including fear of humans, can be reduced when there is a partial concealment as in the case of SPS. This leads to improve the interactions between humans and animals, as well as ease of management (Mancera and Galindo 2011). On the other hand, food selection in the SPS results in greater control of the animal in its environment, with better social performance (Améndola et al. 2016).
Recently, Mancera et al. (2018) established, in cattle farms from southeast of Mexico, a better body condition, less leakage distance and tegument damage in farms with a tree cover from 22 to 35 % compared to those with low coverage (2 %), which implies favorable effects on animal welfare.
Likewise, Améndola et al. (2018), when comparing SPS with monoculture, found that daily feeding time was longer in monoculture, rumination duration was higher in the SPS, feeding time was decreased in relation to temperature-humidity index and this suggests that forage availability and shade access in the SPS allow cattle to rest longer and increase rumination, while cattle in monoculture spend more time searching for food during daylight hours. It is necessary to relate this rumination effect with methane emission.
On the other hand, positive effects of SPS on reproduction are assumed, such as puberty reduction, estrous cycle regularity, improvement of libido in sirer and semen quality, increase of conception rate and reduction of embryonic losses (Pérez-Hernández and Díaz-Rivera 2008).
SOME EXPERIENCES IN THE PRODUCTION OF CALVES IN THE TROPICS WITH THE USE OF TREES AND AGRICULTURAL AND AGRO-INDUSTRIAL BY-PRODUCTS (AAB)
This study presents some results of the proposed use of local resources (trees + AAB) to improve production efficiency and this should allow a better participation in calf sale in the market. In general, there are low weaning weights and ignorance of feeding strategies at this stage.
In this context, in a first case the results of 160-day-old calves are presented in a dual purpose system, where the offspring consume residual milk, plus a grazing area of Cynodon plectostachyus, with different types of supplements, mainly the use of 15 and 30 % of inclusion of a mixture of trees (Gliricidia sepium + Leucaena leucocephala) plus maize stubble (40%), connotation that implies a lower dependence on inputs outside the farm (table 5). The difference in DWG of almost 0.100 kg in favor of the conventional option is acceptable if the independence of the AAB option is taken into account, by incorporating local products it avoids the commercial purchase of food. It is considered that the present strategy has greater production potential if it is not limited by the availability of grass or by the systematic contribution of the supplement.
Table 5 Composition of rations with different inclusion levels of tree legumes (Gliricidia sepium and Leucaena leucocephala)
In a second experience, the potential of animals and the feeding system was demonstrated with the greater use of AAB equivalent to 70 % of the ration (cottonseed meal 9 %, sorghum 18 %, molasses 13 %, poultry manure 17 %, maize stubble 40 %, urea 0.9%, ammonium sulfate 1%, minerals 1% and common salt 1%), with 120-day-old brown Swiss animals, 110 kg of liveweight in a dual purpose system in a 94-day trial, where 1.249 kg/day of DWG was achieved for a final weight of 228 kg at weaning and an intake 5.326 kg of dry matter plus residual milk.
In a third experiment (table 6), maize stubble was substituted for Cenchrus purpureum cv. Cuba CT- 115 hay and the fruit of Crescentia alata was included as a strategy in the development of calves, where the hay of grasses and the fruit represented 66 % of the ration. In addition to improving the productive performance of growing animals, the availability of a perennial forage, coupled with its greater biomass production, it is transformed into a better productive strategy.
Previous results originated the proposal for the development of calves in the cow-calf system, grazing Cenchrus purpureum cv. Cuba OM-22, Cynodon plectostachyus, Megathyrsus maximus cv. Mombasa in monoculture or the same species combined with Morera spp and L. leucocephala in low density, as well as Cynodon plectostachyus with protein bank of L. leucoephala. Calves are kept for the first 30 days with the mother and later, until day 100, they are separated from the mother for six hours in the morning (from 7 am to 1 pm). During this time, they are offered a pre-weaning food. These animals are weaned at seven months with a DWG of 0.939 ± 0.168 and weight of 232 ± 37 kg LW. It is considered that this alternative management of the offspring has a potential of 1.281 kg of DWG.
Table 6 Comparison of two integral rations of fresh basis with agricultural and agroindustrial residues in the development of calves under double purpose systems, comparing two forage sources
To this productive approach in Colima, Mexico, it is added the possibility of a market in a win-win integration, where calves are destined for national consumption and export. In the case of export, it is associated with age, weight, breed type and health (tick control, internal deworming, brucella tests and tuberculosis) among the biological aspects. Regarding the administrative aspects, the distance from the ranch to the storage, availability of vehicle for transport, plus the organization of producers for the sale of calves, as well as accounting elements, factors that, directly or indirectly, impact the price of the weight to the farmer. To meet these requirements, they have an extra in the sale price of up to 10% kg, although it is necessary to point out that price can be variable and responds to external elements, it is considered that all these elements allow to improve productive systems of tropical cattle rearing.
CONCLUSIONS
Mitigation and adaptation strategies carried out in Mexico guide the process for obtaining resilient systems, although there are greater contributions in some areas, they should be identified and combine efforts to develop research and application of knowledge in those topics that are little studied, and, this way, support the development of sustainable cattle rearing.
From a social perspective of a family scale, the development of resilient cattle rearing systems based on forage trees, plus agricultural and agroindustrial residues, is an opportunity for these systems to endure, as it favors their transformation and evolution to sustainable systems.
