Browsing by Author "Vera, Raul"

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    A SIMULATION MODEL OF MESOPHYTIC PERENNIAL GRASSLANDS
    (INST INVESTIGACIONES AGROPECUARIAS, 2012) Castellaro, Giorgio; Aguilar, Claudio; Vera, Raul; Morales, Luis
    Grasslands are complex ecosystems and their processes are affected by soil, meteorological, and management variables. In this context, dynamic simulation models are useful to understand these processes and to design grassland use strategies. The aim of this study was to develop and validate a simulation model of perennial pasture growth based on soil and climate variables. A first approach considered that soil fertility levels were adequate; therefore, soil water availability and phytomass level were the main variables affecting pasture growth. The subroutines considered were water balance, pasture growth, and root biomass dynamics. The hypotheses regarding the functioning of the system were formulated as a group of equations which were solved numerically with a program written in Visual Basic (R). Model validation was performed by statistical comparison between simulated DM and DM obtained from experiments conducted in Valdivia (39 degrees 47' S., 73 degrees 15' W; 9 m a.s.l.). In these experiments we measured DM accumulation on naturalized grassland and ryegrass (Lolium perenne L.)-white clover (Trifolium repens L.) pastures under frequent defoliation. Soil data, temperature, solar radiation, and rainfall were obtained from a meteorological station located in Valdivia. The coefficient of determination between simulated values and those measured in the experiments were higher in the DM accumulation (R-2 = 98%) simulations. When pasture was subjected to frequent defoliation, the degree of fit of the model was lower (R-2 = 60%); however, the model was able to predict the trend in the data.
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    Adaptation strategies based on the historical evolution for dairy production systems in temperate areas: A case study approach
    (2020) Toro-Mujica, Paula; Vera, Raul; Pinedo, Pablo; Bas, Fernando; Enriquez-Hidalgo, Daniel; Vargas-Bello-Perez, Einar
    Dairy production systems are heterogeneous as they are influenced by farm location and structure, markets, environmental conditions, and the producers' preferences and peculiarities. A typology of the existing dairy systems in Chile was developed with the objective of identifying homogenous groups that would allow for the characterization of adaptation strategies to changing environmental, social, technological, political and economic variables. Multivariate analyses were performed on data from official surveys carried out in 2009, 2011, 2013, and 2015. Six groups (I-VI) were identified representing 26.9%, 21.5%, 21.6%, 14.6%, 6.8% and 8.6% of the population surveyed. Group I was the largest, and it included non-specialized commercial dairies. Group II clustered semi-extensive, medium to large dairies that rely mostly on high yielding improved pastures. Group III included small, semi-extensive commercial farms that make a more intense use of pastoral resources, such as sown pastures and improved native grasslands. Groups IV, V, and VI corresponded to specialized dairies, highly market-oriented, that use annual forages to supplement intensively managed and planned pastures, but that differ in size and some management strategies. The observed temporal changes and adaptations over time were closely linked to farm size, intensity in the use of various technologies, the number and the breed of the dairy cows, and the presence of other agricultural activities in the property. The effect of variable prices of milk and system inputs differed by group. Given the social and economic importance of dairies throughout Central and Southern Chile, a number of interventions are proposed, including technical modifications, extension initiatives, and changes in policies.
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    FEEDING DRY OLIVE CAKE MODIFIES SUBCUTANEOUS FAT COMPOSITION IN LAMBS, NOTING CAKE RESISTANCE TO DEGRADATION AND PEROXIDATION
    (INST INVESTIGACIONES AGROPECUARIAS, 2009) Vera, Raul; Aguilar, Claudio; Lira, Rodrigo; Toro, Paula; Barrales, Luis; Pena, Ivan; Squella, Fernando; Perez, Patricio; Quenaya, Javiera; Yutronic, Hanja; Briones, Ignacio
    The purpose of this experiment was to determine the extent to which lamb carcass quality and fat composition could be altered by applying a dry olive cake-based ration instead of a conventional ration or pasture feeding. Three treatments were compared in a completely randomized experiment using 36 single male Suffolk Down lambs with an initial age and live weight of 80 d and 25 kg, respectively. The three treatments were: (a) suckling lambs kept with their mothers on annual Mediterranean grassland (GRAZE); (b) weaned stall-fed lambs on a control ration (CONC); and (c) weaned stall-fed lambs on an olive cake-based ration (CAKE). At the end of the 28-d experimental period, lambs were slaughtered, carcass quality evaluated, and samples of subcutaneous fat analyzed for fatty acids. Treatments did not differ in weight gain or carcass weight and quality, but highly significant differences were found in several fatty acid contents. CAKE animals had reduced palmitic acid as well as increased oleic and stearic acid contents. Atherogenic and thrombogenic indices improved with cake feeding. Principal component and discriminant analyses clearly differentiated treatments suggesting they could be applicable for traceability purposes. A laboratory experiment demonstrated that with or without added vitamin E, the dry olive cake did not alter its lipid properties with increased storage time.
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    MODELLING SUPPLEMENTATION STRATEGIES FOR BEEF STEER REARING AND FATTENING SYSTEMS IN SOUTHERN CHILE
    (INST INVESTIGACIONES AGROPECUARIAS, 2009) Toro, Paula; Catrileo, Adrian; Aguilar, Claudio; Vera, Raul
    A mathematical model was developed to analyze beef production systems in Southern Chile. The study considered the identification of the main components of systems under different beef steer management strategies, using pasture with or without supplementation and back grounding cattle on pasture followed by a winter period of confined feeding with pasture silage and concentrates. Validation of model outputs using 200 kg LW Hereford steers against real experimental data showed no significant differences (P >= 0.01) between simulated and observed final weights. In order to analyze the interaction between the stocking rate (SR) and supplementation, three SR of 2, 2.5 and 3 steers ha(-1) with and without pasture silage supplementation at the rate of 5 kg DMd(-1) steer(-1) for the length of the entire period were simulated. Means were compared by the least significant difference (LSD, P <= 0.05). Significant differences were found in terms of final weights, which decreased with increasing SR regardless of the supplementation level, although silage supplementation tended to reduce differences between SR. A second set of simulation runs was carried out to simulate on-farm finishing of the steers through a final phase of confined feeding based on a ration of silage and concentrates. Final weights differed between SR and systems and results showed that the optimum corresponded to 2.5 steers ha(-1), since at this SR the largest income corresponded to the smallest mean cost. It is concluded that a stocking rate of 2.5 steers ha(-1) is feasible if winter supplementation is available, independently of a finishing period in feedlot.