Abstract Traditional Zacazonapan cheeses have unique organoleptic characteristics and are characterized by being linked to the territory of origin. In the maturation process, there are many interactive variables that are responsible for physical, chemical, biological and structural changes. In order to evaluate the bacteriological evolution of artisanal cheeses during their maturation under non-controlled conditions in two production periods, samples of raw milk and cheese were collected at 0, 30, 60, 120 and 150 d of maturation. The presence of molds and yeasts (MaY), mesophilic aerobic bacteria (MAB), Staphylococcus spp. (Staph), total coliforms (TC), fecal coliforms (FC), Salmonella spp. (Salm) and Listeria spp. (List) was determined. The average microbial load was 9.68, 9.38, 8.55 and 8.10 log10 CFU/g of cheese for MaY, MAB, Staph and TC respectively, as well as 2.68 log10 MPN/g of cheese for FC. Salm was not detected but List was. The microbiological evolution of Zacazonapan matured cheese had counts that exceed the maximum levels of the Official Mexican Standard 243 SSA1 2010.

Resumen Los quesos tradicionales Zacazonapan tienen características organolépticas únicas y se caracterizan por estar vinculados al territorio de origen. En el proceso de maduración se tienen numerosas variables interactivas que son responsables de los cambios físicos, químicos, biológicos y estructurales. Con el objetivo de evaluar la evolución bacteriológica de quesos artesanales durante su maduración bajo condiciones no controladas en dos épocas de producción, se colectaron muestras de leche cruda y de queso a los 0, 30, 60, 120 y 150 días de maduración. Se determinó la presencia de mohos y levaduras (MyL), bacterias mesófilas aerobias (BMA), Staphylococcus spp. (Staph), coliformes totales (CT), coliformes fecales (CF), Salmonella spp. (Salm) y Listeria spp. (List). La carga microbiana promedio fue 9.68, 9.38, 8.55 y 8.10 log10 UFC/g de queso para MyH, BMA, Staph y CT respectivamente, así como 2.68 log10 NMP/g de queso para CF. No se detectó Salm pero si List. La evolución microbiológica del queso madurado Zacazonapan presentó conteos que superan los niveles máximos de la Norma Oficial Mexicana 243 SSA1 2010.

Resumen El objetivo del presente estudio fue caracterizar el ensilaje de maíz acorde a su composición química, a su rendimiento, así como a su producción de leche prevista. Se realizó una búsqueda en estudios relacionados al rendimiento del ensilado de maíz, a la densidad, a la composición química (MS, PB, FDN, almidón) y a la digestibilidad de materia seca (DMS). En este estudio fueron analizadas 41 variedades de maíz de regiones templadas y 101 variedades de maíz de origen tropical. Se determinaron la energía neta de lactancia (ENL Mcal/kg MS), los kilogramos de leche por t de ensilaje (kg de leche/t MS), y los kilogramos de leche por hectárea de ensilaje (kg de leche/ha). Se llevó a cabo un análisis cluster a partir del cual fueron obtenidos seis CL del ensilaje de maíz. El CL1 incluyó digestibilidad de materia seca, proteína bruta, fibra detergente neutro, ENL y kg de leche/t MS. El CL2 se caracterizó por ser el ensilaje de maíz con el mayor número de plantas por hectárea y FDN. El CL3 incluyó el mayor contenido de ceniza. El CL4 se compuso de valores intermedios en todas las variables. El CL5 incluyó el mayor rendimiento de forraje (t MS/ha) y kg de leche/ha, mientras que el CL6 incluyó el mayor kg de leche/t. En general, el CL1 fue el que presentó el mayor valor de DMS y ENL, produciendo como resultado más leche por t MS. Los resultados sugirieron que la opción ideal es el ensilaje de maíz con mayor rendimiento de forraje y más del 35 % MS (CL5), puesto que produjo más kg de leche por hectárea.

Abstract The objective of the present study was to characterize maize silage according to chemical composition, maize silage yield, as well as their predicted milk production. A search was made on studies related to maize silage yield, density, chemical composition (DM, CP, NDF, starch), and dry matter digestibility (DMD). In this study, 41 maize varieties from temperate regions and 101 maize varieties from tropical origin were analyzed. The net energy of lactation (NEL Mcal/kg DM), kilograms of milk per t of silage (kg of milk/t DM), and kilograms of milk per hectare of silage (kg of milk/ha) were determined. A cluster (CL) analysis was performed, and six CL of maize silage were obtained. The CL1 included digestibility for dry matter, crude protein, neutral detergent fiber, NEL, and kg of milk/t DM. CL2 was characterized by maize silage with the highest number of plants per hectare and NDF. CL3 included the highest ash content. CL4 consisted of intermediate values for all variables. CL5 included the highest forage yield (t DM/ha) and kg of milk/ ha whereas CL6 included the highest kg of milk/t. Overall, CL1 resulted in the highest DMD and NEL, producing more milk per t DM. Results suggested that the ideal option is maize silage with a higher forage yield and more than 35 % DM (CL5) since this produces more kg of milk per hectare.

Abstract The partition of the gross energy intake (GEi) by heifers, the energy density, metabolicity of the diet (qm), and the Ym factor were estimated, by the open circuit respiration chamber technique. Four heifers of 206 ± 39.7 kg of live weight and 12 ± 0.93 months of age were used in a completely randomized design. The heifers were randomly assigned to two diets: Diet A consisted of 74% corn silage + 26% commercial concentrate and diet B 100% corn silage. A t-test was used for analysis of results. Dry matter intake (DMI), digestibility of the DM, Ym factor and methane yield (CH4 g kg−1 DMI) for both diets were different (P < 0.05). In the present study we were able to estimate the partitioning of the GE consumed by the experimental animals; as well as the energy density, the Ym and qm factors of the diet.

Resumen Se estimó la partición de la energía bruta consumida (EBi) por novillonas, la densidad energética y metabolicidad de la dieta (qm), y el factor de partición de la energía hacia metano (Ym), por la técnica de cámaras de respiración de circuito abierto. Se utilizaron cuatro novillonas de 206 ± 39.7 kg de peso vivo y 12 ± 0.93 meses de edad; distribuidas en un diseño completamente al azar y dos dietas: dieta A con 74% de ensilado de maíz + 26% de concentrado y dieta B con 100% de ensilado de maíz. Se utilizó una prueba de t para el análisis de resultados. El consumo de materia seca (CMS), digestibilidad, factor Ym y el rendimiento de metano g kg−1 de CMS, para ambas dietas fue diferente (P < 0.05). Se logró estimar la partición de la EBi, la densidad energética y los factores Ym y qm de la dieta.

RESUMO: O objetivo deste estudo é avaliar o efeito do Pithecellobium dulce, Tagetes erecta e o Cosmos bipinnatus na emissão do metano, a produção de leite e de ingestão diária de matéria seca pelo gado. Um desenho experimental do quadrado latino 4x4 foi usado, com quatro vacas da raça Holandesa, multíparas, de 553±72,4kg, no seu segundo terço da lactação e rendimento médio de leitedo de 17,3±3kg/dia. O experimento durou 92 dias e foi dividido em quatro períodos de 23 dias cada um. Das vacas tinham acesso livre a milho e silagem de alfafa, numa proporção de 50:50, com 4kg de concentrado por dia, com acesso a água ad libitum. Os tratamentos consistiram na ingestão de 0,5kg por dia, com as plantas experimentais; as vacas no tratamento de controle não receberam nenhuma planta, porém, elas receberamum tratamento, em cada um dos quatro períodos. O C. bipinnatus reduziu significativamente a produção de metano em 16% (P<0,05), em comparação com a dieta controle. A produção de leite, sua composição e o consumo de matéria seca não foram afetados (P>0,05) pelo uso de C.bipinnatus ou outras espécies de plantas. A ingestão com doses baixas de C. bipinnatus, que é uma planta arbustiva com um centéudo moderado de taninos, mostrou ter potencial para reduzir a produção de metano ruminal em vacas leiteiras.

ABSTRACT: The aim of the present research was to evaluate the effect of Pithecellobium dulce, Tagetes erecta and Cosmos bipinnatus on methane emission, milk yield and dry matter intake in dairy cattle. A 4×4 Latin square experimental design was employed, using four multiparous Holstein cows of 553±72.4kg body weight, at mid lactation and average milk yield of 17.3±3kg/day. The experiment lasted 92 days, divided into four experimental periods of 23 days each. All cows had free access to maize and alfalfa silage in a 50:50 proportion, 4kg of concentrate/day and ad libitum access to water. Treatments consisted in supplementation of 0.5kg/day of the experimental plants, with one control treatment without supplementation. Each cow received one of each treatment in turn during one of the four periods. The C. bipinnatus reduced methane production by 16% (P<0,05) in comparison with the control diet. Milk production, milk composition and dry matter intake were not affected (p>0 0.05) by the use of C. bipinnatus or any other plant species. Supplementation at low doses of C. bipinnatus showed a reduction in ruminal methane production in dairy cows.

ABSTRACT In this work we compared the effects of two ventilation methods on the chemical composition of four livestock manure compost. We conducted four manure composting experiments (Exp) with two ventilation methods: manually with a shovel (Vm), and with perforated polyvinyl chloride (Vt). Exp 1 was designated cattle manure compost (CBo + Vm, CBo + Vt); Exp 2, goat manure compost (CCa + Vm, CCa + Vt); Exp 3, horse manure compost (CEq + Vm, CEq + Vt), and Exp 4, sheep manure compost (COv + Vm, COv + Vt). A completely randomized design was used in each experiment, with three repetitions. A one-way analysis of variance was conducted using the Minitab program and Tukey’s test (p < 0.05) to compare methods. We analyzed temperature, hydrogen potential (pH), electric conductivity (EC), organic matter (OM), organic carbon (C), total nitrogen (N), carbon/nitrogen ratio (C/N), phosphate (PO4), potassium (K), magnesium (Mg), sulfate (SO4), calcium (Ca), sodium (Na), iron (Fe), manganese (Mn), boron (B), zinc (Zn) and copper (Cu). There were highly significant differences in the temperatures observed with the different treatments in the experiments (p = 0.000). No statistical differences were observed in the chemical composition in CBo, CCa and COv based on the ventilation method used (p > 0.05). Statistical differences in C/N were found in CEq + Vt (p = 0.049). The ventilation methods did not impact the chemical characteristics of the cattle, goat and sheep manure composts, but in CEq it was found that placing plastic tubes in the compost piles facilitated greater degradation of the OM and reduced the C/N. Both ventilation methods are recommended in CBo, CCa and COv. And the ventilation method with tubes is recommended in CEq.

RESUMEN Este trabajo comparó el efecto de dos métodos de ventilación en la composición química de cuatro compost de estiércoles pecuarios. Para cada tipo de estiércol mezclado se realizó un experimento de compostaje. En cada experimento (Exp) se ensayaron dos métodos de ventilación: manual con pala (Vm) y con tubos de policloruro de vinilo perforados (Vt). El Exp 1 se denominó compost estiércol bovino (CBo + Vm, CBo + Vt), el Exp 2 compost estiércol caprino (CCa + Vm, CCa + Vt), el Exp 3 compost estiércol equino (CEq + Vm, CEq + Vt) y el Exp 4 compost estiércol ovino (COv + Vm, COv + Vt). Durante el proceso se analizaron temperatura, potencial de hidrogeno (pH), conductividad eléctrica (CE), materia orgánica (MO), carbono orgánico (C), nitrógeno total (N), relación carbono/nitrógeno (C/N), fosfato (PO4), potasio (K), magnesio (Mg), sulfato (SO4), calcio (Ca), sodio (Na), hierro (Fe), manganeso (Mn), boro (B), zinc (Zn) y cobre (Cu). Para cada experimento se utilizó un diseño completamente aleatorizado con tres repeticiones. En las variables de composición química se realizó un análisis de varianza de un factor utilizando el programa Minitab y las medias se compararon con la prueba de Tukey (p < 0.05). La temperatura en cada experimento mostró diferencias significativas entre tratamientos (p = 0.000). Los productos provenientes de CBo, CCa y COv no presentaron diferencias en la composición química por el método de ventilación (p > 0.05). El producto proveniente de CEq + Vt presentó menor relación C/N (p = 0.049). Los métodos de ventilación no influyeron en las características químicas de los compost de estiércol bovino, caprino y ovino, sin embargo, en el compost de estiércol equino al colocar tubos en las pilas de compostaje, se favoreció la degradación de la MO y redujo la relación C/N. Se concluye que los dos métodos de ventilación se recomiendan en los CBo, CCa y COv. Y el método de ventilación con tubos se recomienda en el CEq.

ABSTRACT: It has been shown that tannins in the foliage of trees and shrubs can reduce methane (CH4) production in the rumen. The aim of the present paper was to evaluate the potential of five tanniferous browse plant species, native to temperate central Mexico, to reduce in vitro methane production. The in vitro gas production technique and gas chromatography were used to evaluate the effect of the inclusion of these plants at three inclusion levels (10, 20 and 30 %) in an experimental diet. A factorial experimental arrangement with the five plant species and four levels of inclusion was used. Gas production was monitored throughout 72 h of incubation and methane production was recorded after 24 h. The results showed that a significant decrease in methane production was observed with all plants at 10 % inclusion level (P < 0.001), and that the highest reduction (> 26 %) was observed with Amaranthus spinosus and Commelina coelestis at 20 % and 30 % inclusion respectively in comparison to the control diet. However, the digestibility of the experimental diet declined at these inclusion levels. It was concluded that all the tested plants reduced methane production at all inclusion levels; however, the best tradeoff between methane reduction and tannins' associated negative effects on diet digestibility was achieved at the 10 % inclusion level.

RESUMEN: Se ha demostrado que los taninos en el follaje de los árboles y arbustos pueden reducir la producción de metano (CH4) en el rumen. El objetivo del estudio fue evaluar el potencial de cinco especies de plantas arbustivas, nativas de la región de clima templado del centro de México, para reducir la producción in vitro de metano. Los follajes fueron adicionados a 0, 10, 20 y 30 % en base seca a una dieta experimental en un diseño factorial de cinco plantas por cuatro niveles de inclusión. La producción de gas in vitro se monitoreó a lo largo de 72 h de incubación y la producción de metano se registró después de 24 h. Los resultados mostraron una disminución significativa en la producción de metano con todas las especies de plantas a un nivel de inclusión de 10 % (P < 0.001), mientras que la reducción más alta (> 26 %) se observó con Amaranthus spinosus y Commelina coelestis a niveles de inclusión de 20 % y 30 %, respectivamente, en comparación con la dieta control. Sin embargo, la digestibilidad de la dieta experimental disminuyó al aumentar los niveles de inclusión. Se concluyó que las plantas evaluadas en todos los niveles de inclusión redujeron la producción de metano, sin embargo el mejor balance entre la reducción en la producción de metano y los efectos negativos sobre la degradación de la dieta asociados a los taninos se alcanzó a un nivel de inclusión del 10 %.

Abstract Measurement of greenhouse gas emissions is highly relevant in assessing the environmental impact of agricultural systems. Methane produced by enteric fermentation of ruminants represents an important part of all anthropogenic emissions of greenhouse gases in Latin America, where there is a large production of ruminants. Currently, the efforts of Latin American countries are focused more on the quantification of methane emissions and the calculation of national inventories than on mitigation. In this paper the data obtained so far in different experiments, in terms of in vivo determination of methane emissions in the countries of Latin America are exposed. This, with the intention of discussing and making known the current panorama and the zone progress in terms of measurement of the environmental impact of this gas and the development of strategies to reduce its production by ruminants. Finally the challenges that are faced in the future in the investigation on the subject are marked.

Resumen La medición de la emisión de gases de efecto invernadero es altamente relevante en la evaluación del impacto ambiental de los sistemas agropecuarios. El metano producido por la fermentación entérica de los rumiantes representa una parte importante de todas las emisiones antropogénicas de gases de efecto invernadero en América Latina, donde hay una gran producción de rumiantes. Actualmente, los esfuerzos de los países latinoamericanos están enfocados más en la cuantificación de las emisiones de metano y el cálculo de los inventarios nacionales que en la mitigación. En este ensayo se exponen los datos obtenido hasta ahora en diferentes experimentos, en término de determinación in vivo de las emisiones de metano en los países de América latina. Esto, con la intención de discutir y dar a conocer el panorama actual y los avances de la zona en cuanto a la medición del impacto ambiental de este gas y el desarrollo de estrategias para reducir su producción por los rumiantes. Finalmente se marcan los retos que se enfrenta en el futuro la investigación sobre el tema.

ABSTRACT Ruminant animals contribute significantly to methane emissions in tropical regions. Nonetheless, there are few facilities available in those regions of the world for in vivo measurement of methane production in cattle. The aim of the present work was to describe the design, construction and operation of respiration chambers for in vivo measurement of methane production in cattle in Mexico. Locally available materials were used in the construction. Walls, roof and doors were constructed of thermic panels with two windows of acrylic at the front so the animal can be observed at all times. Chambers have an air volume of 9.97 m3. Air is drawn from the chamber at a rate of 500 L/min by the effect of mass action flow generators. Methane was measured in air samples with an infrared analyzer. Chambers operate under a slight negative pressure of around -500 Pa. Air temperature inside the chambers is kept at 23 °C with an air conditioner, while relative humidity is maintained at 55 % with a dehumidifier. Functioning of the chambers was evaluated in Bos indicus, Nelore cattle fed Taiwan grass (Pennisetum purpureum) and a concentrate (18 % crude protein), and measurements were made during runs of 23 h duration. Methane production was on average 173.2 L per day, while the emission factor was 17.48 L methane per kilogram o dry matter consumed. It concludes that this respiration facility is capable of measuring methane production accurately in cattle fed tropical rations.

RESUMEN Los rumiantes contribuyen significativamente a las emisiones de metano en las regiones tropicales. Sin embargo, hay pocas instalaciones disponibles para la medición in vivo de estas emisiones. Por lo anterior, el objetivo del presente trabajo fue describir el diseño, construcción y operación de cámaras de respiración para la medición in vivo de la producción de metano de bovinos en México. En la construcción se utilizaron materiales disponibles localmente. Las paredes, el techo y las puertas se construyeron de paneles térmicos con dos ventanas de acrílico, en ambos lados, en la parte delantera. Las cámaras tienen un volumen de aire de 9.97 m3. El aire de la cámara se extrae con una bomba de flujo de masas a una velocidad de 500 L/min. El metano mezclado en las muestras de aire se cuantificó con un analizador de infrarrojo. Las cámaras funcionan bajo presión negativa de -500 Pa. La temperatura y humedad relativa se mantiene a 23 °C y 55 %, respectivamente. El funcionamiento de las cámaras se evaluó utilizando ganado Bos indicus, de la raza Nelore, alimentado con pasto de Taiwán (Pennisetum purpureum) y un concentrado con 18 % de proteína cruda; y se realizaron mediciones con las cámaras durante 23 h. La producción de metano fue de 173.2 L/día, mientras que el factor de emisión fue de 17.48 L de metano/kg de materia seca consumida. Se concluye que las cámaras de respiración pueden medir con precisión la producción de metano en ganado Nelore consumiendo raciones tropicales.

RESUMO: Este estudo analisou as características dos ácidos graxos na carne de cordeiros alimentados com pastagem e suplementados com diferentes fontes de proteína. Trinta cordeiros Suffolk foram utilizados (37,2±5,4kg BW) que pastavam em azevém perene (Lolium perenne) (12h d-1) e suplementados com (30g kg-1 PV0,75) com azevém feno (RGH), ou concentrados formulado com farinha de peixe (FSM) ou farelo de soja (SBM). Os resultados mostram um efeito sobre o total SFA, sendo mais elevada do que SBM RGH (P=0,033). SBM e FSM mostrando o maior teor total de MUFA vs. RGH (P=0,001). O teor total de AGPI foi maior para RGH>EFM>SBM (P=0,001). Concluindo que há uma variação no teor de ácidos graxos dependendo da fonte de proteína utilizada na suplementação emanimais pastoreados, o teor de PUFA foi maior para ovinos mantidos em comparação com os suplementado com EFM ou SBM.

ABSTRACT: This study examined the characteristics of the fatty acids profile in the meat of lambs fed grazing and supplemented with different PUFA sources. Thirty Suffolk lambs were used (37.2±5.4kg BW), grazing on perennial ryegrass (Lolium perenne) (12h d-1) and supplemented (30g kg-1 BW0.75) with ryegrass hay (RGH), or supplements formulated with fishmeal (FHM) or soybean meal (SBM). Lambs were used in a completely randomized design. Results showed an effect on total SFA, with SBM higher than RGH (P=0.033), and SBM and FHM showing higher MUFA content compared with RGH (P=0.001). Total PUFA content was higher for RGH, followed by FHM and with the lowest content for SBM (P=0.001). Concluding that there is a variation in fatty acid content depending on the lipid-protein source used in supplementation in grazing sheep, the content of PUFA was higher for grazing lambs supplemented with RGH compared with those supplemented with FHM or SBM.

Abstract: The effect of adding different proportions 0, 1, 2, 3, 4, 5 y 6 % of Thevetia peruviana (TP) and avocado fruit Persea americana (AG) seed oils, was evaluated over gas production (GP), methane (CH4) dry matter digestibility (IVDMD) and neutral detergent fiber digestibility (IVDNDF) in a cultured bovine rumen fluid system. For data analysis a lineal model of orthogonal contrasts was used. Finding an effect of both oils (P < 0.001) over GP from 4 % inclusion, with an average production of 220 cm3. In the methane production, a decrease from 3 % inclusion was found in both treatments (P < 0.0001), with a linear and quadratic effect when the oils doses were increased. The IVDMD of control treatment was 67.2 %, significantly decreasing from levels 4, 5 and 6 % in both treatments, IVDNDF showed a similar trend, declining significantly in both treatments from 4 % inclusion in both oils. For all the evaluated variables an effect of the inclusion level was found, but not an effect related to the type of oil. The 3 % of TP and AG oil supplementation reduces CH4 production without affecting gas production, either forage digestibility, so this level could be the more appropriate to evaluate its potential in vivo conditions.

Resumen: Se evaluó el efecto de la adición de proporciones 0, 1, 2, 3, 4, 5 y 6 % de aceites de semillas de Thevetia peruviana (TP) y frutos de aguacate Persea americana (AG) en cultivos in vitro de fluido ruminal bovino sobre la producción de gas (PG), metano (CH4), la digestibilidad de materia seca (DIVMS) y fibra detergente neutra (DIVFDN). Se utilizó un modelo lineal de contrastes ortogonales para el análisis de datos. Se encontró efecto (p < 0.0001) en la inclusión de ambos aceite sobre la PG a partir del 4 %, con una producción promedio de 220 cm3. En la producción de CH4, se encontró una disminución a partir del 3 % de inclusión de ambos aceites (p < 0.0001), con efecto lineal y cuadrático al aumentar la dosis. La DIVMS del tratamiento testigo fue del 67.2 %, disminuyendo significativamente a partir de los niveles 4, 5 y 6 % de ambos aceites. La DIVFDN, mostró una tendencia similar, disminuyendo en ambos tratamientos de manera significativa a partir del 4 % de inclusión. Para todas las variables evaluadas se encontró un efecto del nivel de aceite, pero no se observó efecto del tipo de aceite. El nivel del 3 % de suplementación de aceites de TP y AG redujo la producción de CH4, sin afectar la producción de gas y digestibilidad del forraje, por lo que puede ser el nivel más apropiado para evaluar su potencial en condiciones in vivo.

Abstract: Objective: To determine the prevalence and the degree of contamination by molds and yeasts (M&Y), aerobic mesophilic bacteria (AMB), total coliforms (TC) and Salmonella spp. (S). These microorganisms were considered indicators of quality and hygiene in the manufacturing environment of Zacazonapan cheese. Materials and methods: Samples from five cheese dairies at Zacazonapan municipality were collected. The samples were collected directly from hands, water, milk, curd, cheese and surface of utensils for cheese making. Results: All surfaces sampled were contaminated, there was an evident lack of hygiene in the cheese making process, the microorganisms count during cheese manufacturing were: for milk; 6.8, 6.7 and 4.5 log10 CFU/ml for M&Y, AMB and TC, respectively. For cheese, the presence of S was detected and presented the following counting: 9.16, 9.23 and 9.18 log10 CFU/g to M&Y, AMB and TC. Conclusions: The lack of hygiene in dairies and implements for cheese manufacturing represents a risk for human health.

Resumen: Objetivo: Determinar la prevalencia y el grado de contaminación por mohos y levaduras (M&L), bacterias mesófilas aerobias (BMA), coliformes totales (CT) y Salmonella spp. (S) como indicadores de calidad e higiene en el entorno de fabricación del queso de Zacazonapan. Material y métodos: En cinco queserías se obtuvieron muestras de agua, leche, cuajo y queso, y de superficie de las manos y de los utensilios que están en contacto con el queso. Resultados: Todas las superficies presentaron contaminación; por lo tanto, se observa falta de higiene al elaborar el queso. Los conteos durante la elaboración de queso fueron, para leche, de 6.8, 6.7 y 4.5 log10 UFC/ml para M&L, BMA y CT, respectivamente. En queso, se detectó la presencia de S y cuentas de 9.16, 9.23 y 9.18 log10 UFC/g para M&L, BMA y CT. Conclusiones: La poca higiene en queserías y utensilios al elaborar el queso representa un riesgo para la salud humana.

Abstract: Objective: To determine the prevalence and the degree of contamination by molds and yeasts (M&Y), aerobic mesophilic bacteria (AMB), total coliforms (TC) and Salmonella spp. (S). These microorganisms were considered indicators of quality and hygiene in the manufacturing environment of Zacazonapan cheese. Materials and methods: Samples from five cheese dairies at Zacazonapan municipality were collected. The samples were collected directly from hands, water, milk, curd, cheese and surface of utensils for cheese making. Results: All surfaces sampled were contaminated, there was an evident lack of hygiene in the cheese making process, the microorganisms count during cheese manufacturing were: for milk; 6.8, 6.7 and 4.5 log10 CFU/ml for M&Y, AMB and TC, respectively. For cheese, the presence of S was detected and presented the following counting: 9.16, 9.23 and 9.18 log10 CFU/g to M&Y, AMB and TC. Conclusions: The lack of hygiene in dairies and implements for cheese manufacturing represents a risk for human health.

Resumen: Objetivo: Determinar la prevalencia y el grado de contaminación por mohos y levaduras (M&L), bacterias mesófilas aerobias (BMA), coliformes totales (CT) y Salmonella spp. (S) como indicadores de calidad e higiene en el entorno de fabricación del queso de Zacazonapan. Material y métodos: En cinco queserías se obtuvieron muestras de agua, leche, cuajo y queso, y de superficie de las manos y de los utensilios que están en contacto con el queso. Resultados: Todas las superficies presentaron contaminación; por lo tanto, se observa falta de higiene al elaborar el queso. Los conteos durante la elaboración de queso fueron, para leche, de 6.8, 6.7 y 4.5 log10 UFC/ml para M&L, BMA y CT, respectivamente. En queso, se detectó la presencia de S y cuentas de 9.16, 9.23 y 9.18 log10 UFC/g para M&L, BMA y CT. Conclusiones: La poca higiene en queserías y utensilios al elaborar el queso representa un riesgo para la salud humana.

Anaerobic fermentation of structural carbohydrates in the rumen of bovines produces waste products such as volatile fatty acids, fermentation heat, carbon dioxide and methane gas. Methane is a greenhouse gas having several times the global warming potential of CO2. The purpose of the present paper is to provide a realistic estimate of the national inventory of methane produced by the enteric fermentation of cattle, based on a simulation model and to provide estimates of CH4 produced by cattle fed typical diets from the tropical and temperate climates of Mexico. Predicted total emission of methane produced by the 23.3 million heads of cattle in Mexico is approximately 2.02 Tg/yr. It was concluded that the modeling approach was suitable in producing a better estimate of the national methane inventory for cattle. It is flexible enough to incorporate more cattle groups or classification schemes, productivity levels and a variety feed ingredients for cattle. The model could also be used to evaluate different mitigation strategies and serve as a tool to design mitigation policies.

La fermentación anaeróbica de los carbohidratos estructurales en el rumen de los bovinos genera productos de desecho como ácidos grasos volátiles, calor de fermentación, bióxido de carbono y gas metano. Este último es un gas de invernadero que tiene un potencial varias veces mayor que el CO2 para inducir calentamiento global. El objeto del presente trabajo es aportar una estimación del inventario nacional de metano producido por la fermentación entérica del ganado bovino en México, realizado a partir del uso de un modelo matemático de simulación. Se hizo una clara diferenciación entre el CH4 producido por bovinos que consumen una dieta típica de las regiones tropicales y aquellos que se alimentan con ingredientes de las regiones templadas de México. Se estimó que la emisión total de metano producido por las 23.3 millones de cabezas de bovinos de México asciende a aproximadamente 2.02 Tg/año. Se concluyó que el modelo desarrollado fue apropiado para producir una mejor estimación del inventario nacional de metano producido por el ganado bovino, ya que es lo suficientemente flexible para incorporar nuevos grupos de ganado o esquemas de clasificación, niveles de productividad y una gran variedad de alimentos para el ganado. El modelo también puede utilizarse para evaluar diferentes escenarios de mitigación y servir como herramienta para diseñar políticas de mitigación.

O objetivo do presente trabalho foi simular o efeito da variação sazonal do clima sobre o valor nutritivo e a produção de matéria seca do capim-estrela e a sua capacidade de apoiar a produção de leite, com ou sem suplementação concentrada, nos sistemas de produção de leite em pequena escala, nas regiões tropicais da região central do México. Foram utilizados dois modelos de simulação, o primeiro modelo simula o crescimento e produção de grama estrela (Cynodon plectostachyus), e o segundo modelo simula o desempenho produtivo de vacas leiteiras. Ambos os modelos foram integrados em um sistema de apoio à tomada de decisão para a produção de leite em regiões de clima tropical (DSSTROP). Previsões do modelo foram validadas por um exercício de calibração, para os quais foram utilizados dados de três experimentos sobre o efeito da suplementação concentrada na produção de leite. As previsões do DSSTROP e os dados obtidos foram comparados através de análise de regressão. Os resultados sugerem que o DSSTROP prevê adequadamente a produção de leite (R2=0,74) para as três experiências simuladas. As previsões DSSTROP sugerem que a produção de leite com base exclusivamente na grama estrela pode ocorrer apenas entre junho a agosto. A maior produção de leite (8,5kg vaca-1 dia-1), sustentada unicamente na grama foi alcançada em junho, seguido por rendimentos mais baixos de cerca de 5kg vaca-1 dia-1, em julho e agosto. O período de produção de leite sem concentrado pode ser explicado pelos efeitos positivos da chuva, observada durante junho-agosto no crescimento do pasto, e devido ao fato de que o valor nutritivoé melhor no início da estação chuvosa. Conclui-se que entre junho-agosto é a melhor época do ano para a base de produção de leite exclusivamente com pasto. Além disso, o uso de grandes quantidades de concentrados pelos agricultores na área de estudo se justifica, pois produção de leite somente com grama estrela não é possível e talvez nem aconselhável.

The objective of the present study was to simulate the effect of the seasonal variation of climate on the nutritional value and dry matter yield of star grass and its capacity to support milk production alone or with concentrate supplementation in small-scale milk production systems in the tropical regions of Mexico. Two mathematical simulation models were used, the first model simulates the growth and yield of star grass (Cynodon plectostachyus), and the second model simulates the productive performance of dairy cows. Both models were integrated in a decision-making support system (DSSTROP). Model's predictions were validated by a calibration exercise for each data set from three experiments on the effect of concentrate supplementation on milk yield. The DSSTROP predictions and the results from the experiments were compared by regression analysis. The results suggest that the DSSTROP adequately predicts milk production (R2=0.74). The DSSTROP predictions suggest that milk production based solely on star grass may occur only between June to August. The highest milk yield (8.5kg cow-1 day-1) sustained solely on grass was achieved in June, followed by lower yields of <5kg cow-1 day-1 in July and August. Milk production without concentrates can be explained by the positive effects of the rain observed during June to August on grass growth, and to the fact that grass quality is best at the beginning of the rainy season. It is concluded that June to August is the best time of the year for milk production base solely on grass. It also was concluded that the use of large quantities of concentrates by farmers may be justified because milk production with star grass alone may not be possible especially during the dry season.

O uso da análise de cinética de produção de gases, em conjunto com a análise de prova de curva e as propriedades químicas da forragem permitem uma melhor descrição das características nutritivas das forragens. Objetivou-se estudar a composição nutritiva e características de fermentação de ruminal de três gramíneas, uma leguminosa e uma mistura composta de pastagens do Planalto Montanhoso Central do México. As amostras representativas de Pennisetum clandestinum (kikuyu grama), Sporobolus indicus (rabo de rato), Eleocharis dombeyana (cana), Trifolium amabile (trevo asteca) mais uma amostra composta foram coletadas durante os meses de Julho, Setembro e Novembro de 2003. Foi utilizada a técnica de produção de gás in vitro (GP). Os perfis de GP foram ajustados ao modelo descrito por PALMER et al. (2005). As diferenças (P<0.001) foram observadas entre espécies e períodos quanto à composição química, matéria orgânica e digestibilidade da fibra em detergente neutro. As diferenças (P<0.05) dos parâmetros de fermentação e cinética de produção de gases mostraram T. amabile e P. clandestinum com fermentação mais intensa, ao passo que S. indicus e E. dombeyana tiveram fermentação limitada. Concluiu-se que a combinação da análise de cinética de produção de gases e o perfil de GP ajustado ao modelo matemático ajudou a descrever as características nutritivas das gramíneas, da leguminosa e da amostra composta de forma mais acurada do que quando um dos métodos foi utilizado de forma isolada.

This paper has two objectives, the first is to determine the chemical composition, gas production parameters and the gas release kinetics, at different stages of maturity, of three grasses and a legume commonly found in long established pastures in Mexico central highland plateau. The second is to combine the gas release kinetics analysis and the GP fitted to a mathematical model in order to improve the biological understanding of the fermentation kinetics obtained from the GP technique. Representative samples of Pennisetum clandestinum (kikuyu grass), Sporobolus indicus (mouse tail), Eleocharis dombeyana (reed), Trifolium amabile (Aztec clover) plus a composite sample were collected in the growing season (July, September and November 2003) and analysed using an in vitro gas production (GP) technique. The accumulated GP was fitted to the model described in PALMER et al. (2005). Significant differences (P<0.001) were observed among species and periods for chemical composition, organic matter and neutral detergent fibre digestibility. Significant differences (P<0.05) were observed regarding fermentation parameters and gas release kinetic, with T. amabile and P. clandestinum being the species with the highest fermentability, whereas S. indicus and E. dombeyana were poorly fermented. P. clandestinum and T. amabile showed higher nutritive value than S. indicus and E. dombeyana. Composite samples were influenced by the chemical and fermentation characteristics of all species. It was concluded that the use of gas release kinetics analysis was useful for differentiating the fermentation kinetic of the soluble and insoluble fraction in the grasses and legume. Therefore by performing both approaches, the gas release kinetics analysis and the GP fitted to a mathematical model, gave a better description of the fermentation kinetic of grasses and the legume was achieved when only one approach had been used.