MODELING GROWTH OF STAR GRASS (Cynodon plectostachyus) IN THE SUBTROPICAL REGIONS OF CENTRAL MEXICO.

The present work describes a mathematical model that simulates growth and biomass production of Star grass in the lowland subtropical areas of Central Mexico. The Star grass model simulates growth of the different plant structures such as the root, stem and shoots, and it has five submodels: growth, photosynthesis, mineral intake, ontogenic and disturbances submodels. The growth submodel simulates nutrient partition and growth of root, stem and leaves. The photosynthesis submodel simulates the transformation of solar energy and carbon into biomass, and it is determined by irradiation, ambient temperature and the leaf area index. The mineral uptake submodel represents the interphase between the soil and the plant, and it simulates a plant’s uptake of nitrogen and phosphorous as well as the different factors that determined their availability, such as soil water content and the mineralization rate. The ontogenic submodel emulates the vegetative phase and the senescence of the plant. The disturbances submodel simulates the effect of factors such as harvest, fire and grazing on the above-ground part of the plant. The original model was developed for C3 plants so it was necessary to modify its parameters for simulating a C4 plant like Star grass. The parameters of soil, drought tolerance, nitrogen content (in the degradable fraction of the plant) and temperatures for maximum and minimum plant growth were modified. The phenological phase of the plant was modified and the reproductive routine was eliminated since Star grass is propagated by stolons and generally remains in the vegetative stage. The re-growth of new shoots begins when soil temperature is above 11o C and soil water content above 0.5. Minimum data set for model development was collected from a sward planted with Star grass and located in the Tejupilco municipality (18º 45´ 30†North and 99º 59´ 07†West) México, and data from literature was also used. Daily climate data was obtained from the local meteorological station. Model predictions were validated with data sets collected from two more swards located in the same region. Results indicated that the model’s predicted dry matter yield during the entire production cycle was very close to observed data (R2=0.92,

CHARACTERISTICS OF THE TEPEQUE CHEESE FROM “LA TIERRA CALIENTE†OF THE STATE OF MICHOACÃN: A CHEESE PRODUCED IN AN INTENSIVE SILVOPASTORAL SYSTEM

The objective of the present work is to describe the characteristics of the Tepeque cheese from “La Tierra Caliente†of the State of Michoacán, Mexico. Its region of origin, manufacturing process, physico-chemical and microbiological characteristics, were investigated. In addition the changes that occurred in the milk and cheese due to the introduction of a feeding system based on the use of an intensive silvo-pastoral system (ISPS) were described. The methodological approach consisted of field visits for data collection, semi-structured interviews to farmers in order to know the milk production systems and the cheese elaboration process. The physical (pH and density) and chemical characteristics (protein, fat, lactose, non fat solids and added water) of the milk used to elaborate the Tepeque cheese were determined. For the cheese the protein, fat, salt, moisture and ash contents and the pH were determined. The microbiological characteristics were determined for both milk and cheese, these included presence of mesophilic bacteria coliforms bacteria, yeast, fungus, Listeria spp. and Staphylococcus aureus. The field study was carried out in 2010; it was divided in two experimental periods of six months each, named rainfall season and dry season. Fifteen milk-cheese producers were sampled, eight of them practice the traditional milk production systems and seven the ISPS. It was observed that the Tepeque cheese is a dairy product of excellent quality from the point of view of its main nutritional components, it is made with good quality milk too and it has a long history and great tradition that is older than 300 years. On the other hand, the cheese elaborated with milk from the ISPS had higher fat content (P0.05). Finally, it was observed that the sanitary characteristics of the milk and cheese were deficient in both systems; this problem is attenuated with the maturing process of cheese since as the cheese matures the number of undesirable bacteria is reduced. Therefore the consumption of matured cheese is recommended

CHEMICAL COMPOSITION OF LEGUMINOUS TREE FOLIAGE AND EFFECT OF POLYETHYLENE GLYCOL ON GAS PRODUCTION AND IN VITRO DIGESTION PARAMETERS

The objective was to determine the chemical composition, digestibility and in vitro digestion parameters in ten legume tree foliage using the in vitro gas-production method with and without polyethylene glycol (PEG). The foliages with higher protein content (P<0.001) (167.1 to 180.3 g/kg DM) were A. cochliacantha, L. esculenta, E. cyclocarpum and A. farnesiana; from the total phenols (P<0.001) (365.9 to 680.6 g/kg DM) L. divaricata, H. brasiletto and C. coriaria and condensed tannins (P<0.001) (35.4 to 88.0 g/kg DM) E. cyclocarpum, A. farnesiana, P. dulce, P. acatlense and G. sepium. The in vitro dry matter digestibility was different (P<0.001) among the foliages. The in vitro gas production (IVGP), in vitro organic matter digestibility, metabolizable energy (ME), gas yield (GY24h), short chain fatty acids (SCFA) and microbial mass production (PMM), were different (P<0.0001) among the foliage as a result of the species. The use of PEG increased (P<0.0001) IVGP, ME, GY24h and SCFA in H brasiletto, C. coriaria, L. esculenta and A. cochliacantha, but affect (P<0.0001) the partition factor and the PMM. The nutritional composition and fermentation parameters in vitro between foliages differ by effect of tree and use of PEG. It is concluded that chemical composition in the foliages affect the digestibility and fermentation parameters and use of PEG increased fermentation parameters in the foliages high in secondary compounds