Luis Ramírez-Avilés

A mixture simplex design to study associative effects with an in vitro gas production technique

A mixture simplex design (special cubic version of Scheffes canonical polynomial) was used to investigate associative effects of feed mixtures incubated using an in vitro gas production technique. The model included the principal effects (single feeds), double and multiple interaction (mixtures of two and three feeds). Two forage trees (Leucaena leucocephala and Lysiloma latisiliquum) were evaluated in two separate incubation batches. Commercial concentrate feed, grass hay and a fodder tree were used to prepare the mixtures in all possible combinations resulting from 0.0, 0.25, 0.50, 0.75 and 1.0 of grass, concentrate and one forage tree per batch. Pressure and gas volumes were monitored up to 168 h. After incubation the residues were used to measure DM and OM digestibility (in vitro dry matter (IVDMD) and in vitro organic matter (IVOMD)). Cumulative gas production (CGP (ml)) profiles were fitted to the equation CGP = a + b(1 - e -kt ). A significant associative response in total gas production (P < 0.01) was found when the forage trees were mixed with the concentrate but not with the grass. Grass and concentrate mixtures increased gas production but the interaction was significant only in the L. latisiliquum batch (P < 0.05). IVDMD and IVOMD were reduced by the inclusion of leucaena in the mixture (P < 0.01). Rate of gas production, k (% h -1 ) was significantly depressed when L. latisiliquum was a component of the mixture (P < 0.01) but not in all remaining mixtures, including those that contained leucaena. It was concluded that mixture simplex designs are useful tools to identify and study in vitro associative effects of feed mixtures.

Influence of livestock systems with live fences of Gliricidia sepium on several soil properties in Tabasco, Mexico

The aim of the current study was to evaluate the effects of two livestock systems, a livestock system with live fences (LSLF) of Gliricidia sepium associated with signal grass ( Brachiaria decumbens ) and a livestock system based on a grass monoculture (LSPM), on specific physical and chemical soil characteristics at different depths and distances from the fence. In each system, we randomly selected 9 plots of 600 m 2 . A completely randomized design was used with a 2 x 3 factorial arrangement in which we analyzed the influence of the livestock systems (LSLF and LSPM), soil strata (0-10, 10-20 and 20-30 cm) and the interaction of both factors using a multivariate analysis of variance. In addition, we performed analysis of variance to determine the effect of distance sampling in the LSLF (0-3, 3-6 and 6-9 m). The LSLFs were associated with higher (P 0.05) at different depths and distances from the live fences. However, the soil pH varied between soil depths in the LSPM. Regarding the physical soil properties, only the sand and clay content varied (P 0.05). Sin embargo, pH del suelo vario entre las profundidades del suelo en los SGMP. En cuanto a las propiedades fisicas del suelo, solo las proporciones de arena y arcilla variaron a diferentes profundidades en ambos sistemas, pero no a diferentes distancias de los sistemas ganaderos con cercas vivas (P≤0.05). Se concluye que los SGCV tienen un enorme potencial para mejorar sustancialmente las propiedades fisicas y quimicas del suelo, siendo una oportunidad para frenar el deterioro de los suelos en sistemas de produccion ganaderos basados en el monocultivo de pasto.

Effects of two intake levels of Leucaena leucocephala on rumen function of sheep

Ruminant production systems based on grass pastures often produce only poor animal performance as expressed by growth or reproductive rates. The nutrient imbalance affecting rumen function is due to low energy and protein intake. The incorporation of leguminous forages such as Leucaena leucocephala, in the diet of ruminants, can stimulate rumen function by providing protein-rich forage (Barros-Rodriguez et al. 2012). This increases the availability of compounds such as ammonia, amino acids and peptides as well as branched short-chain fatty acids, which are produced as a result of degradation of proteins. These substances promote fiber breakdown by acting as ruminal growth activators for rumen bacteria, especially cellulolytic bacteria (Hoover and Stokes 1991). This study aimed to evaluate the effects of 2 intake levels of L. leucocephala (leucaena) on rumen function of sheep fed Pennisetum purpureum.

Effects of weed control and manure application on nutrient fluxes in the shifting cultivation milpa system of Yucatán

Maize (Zea mays L.) cultivation under the shifting cultivation system of Yucatán, Mexico, is normally limited to 2–3 years due to nutrient depletion and weed pressure. This study was undertaken to evaluate the effect of manure application and weed control on partial nutrient budgets for maize, and assess the effect of grain-only or whole-plant harvest on nutrient removal. Two farms were selected near Mérida, Mexico, each including two cultivation years. Maize grain, stem, and leaf fractions were harvested and analyzed for N, P, and K concentrations, and compared to quantities added through manure, to generate partial nutrient budgets. Multiple years of cultivation did not change soil organic matter content while extractable P was reduced (53–62%) at both farms and extractable K was lower (22%) for farm 1. Plant fractions contained similar amounts of N, while P accumulated in grain, and stem and leaf contained the largest K pools. Applied treatments affected crop nutrient removal predominantly through crop yield. Partial nutrient budgets suggested that with stover removal, the lower rate of manure may be sufficient to maintain P, but not N or K; whereas with the higher rate of manure all partial budgets were positive, suggesting nutrient accumulation over time.