Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The truck factor is one of the main components in the estimation of the load demand that pavements will have. For this reason, having reliable truck factors is of utmost importance during the design stage. In the present study, the databases on truck factors calculated between 2007 and 2017 were compiled and analysed by LanammeUCR. More than 15 million heavy vehicles were analysed, distributed on different routes in the country. Given the need to have updated truck factors that take into account the national reality, both during the period without weight control and during the period with, truck factors are generated that are associated with a specific level of reliability and that consider the proportion of vehicles that contribute to their estimate.

The resilient modulus is a measure of the ability of a material to store or absorb energy without experiencing permanent deformation. This is determined by triaxial tests of repeated load and is an important parameter in the analysis and design of flexible pavements. With its value it is possible to predict the mechanical response of the pavement as stresses, deformations and deflections. However, obtaining it is expensive for the equipment involved and not all material laboratories have the test. Because of this, pavement designers use correlations to approximate a resilient modulus value, which generally differs considerably from that obtained with the test. The following research aims to estimate a universal model of a resilient modulus for granular materials that considers variables related to stress states and the basic characteristics of the materials. For this, a linear regression model was generated using ordinary least squares with data from at least 13 different granular materials. The model was validated by statistical indicators obtaining an acceptable goodness of fit.

Hydrated lime is used as an additive for asphalt mixtures, since it enhances the properties of the material in a unique way, enabling a longer service life. In this study, several scientific articles were analyzed in order to understand some of the methods employed of adding hydrated lime to the asphalt mixtures, as well as the optimum amount of hydrated lime that will significantly improve the material’s response towards diverse factors. It was found that the researchers usually add hydrated lime in percentages ranging between 1%-2% in weight of aggregates. Also, in the case of asphalt modified with hydrated lime, the material is stiffer and more resistant to moisture damage. Finally, after this literature review it is concluded that adding 1,5% of hydrated lime the most promising properties were obtained in most of the studies considered.

The Atomic Force Microscope is used to obtain superficial images with high resolution. As well, to acquire information about the mechanical properties of a material. This tool has several operation modes, such as static, dynamic, tapping and contact, among others. It is worth to mention that cantilever has several geometries, then choosing the right one is a crucial step in any investigation that uses AFM. The focus of this article is to give a broad outlook of the AFM, from its operation modes to its applications in asphalt studies. Upon this article, the AFM is highly used in asphalts to analyse the microscopic properties and to understand how these properties impact its macroscopic performance.  

Fabiola Miranda ArgüelloMaster in Civil Engineer of University of Costa RicaResearcher of the Materials and Pavements Division, Pitra, LanammeUCR.Editor of Infraestrutura Vial 1991-2020

The objective of this study was to evaluate the effect of volume of liquid diet on the consumption of concentrate and performance in calves. Sixteen animals were divided into two treatments: the liquid diet treatment with increasing/decreasing order (OC / D), offering 6,8,10,8,6,4,2,1 liters of whole milk per day during the weeks 1, 2, 3, 4, 5, 6, 7 and 8, respectively, and the 6 l.d-1treatment (n = 8), offering 6 liters of whole milk daily from day 0 to weaning (57 days). The data were analyzed with STATISTICA software (StatSoftV10) and Graph Pad Prism V.8.0.2 using the non-parametric Kruskal-Wallis test. Significant results were evaluated with Dunn's test. The non-parametric Mann-Whitney U test was used. The dry matter intake for the OC/D treatment and 6 l.d-1 was different in the third (p <0.001) and seventh week (p = 0.02). The results indicate that in terms of dry matter intake (DM), crude protein (CP) and metabolizable energy (ME) there were no significant differences between treatments, however, there was an effect of these between weeks. The consumption of concentrate at weaning was 0.80 and 0.48 kg (p <0.05) for the OC/D treatment and 6 l.d-1, respectively. The calves that received the OC/D treatment and 6 l.d-1 had an average weaning weight of 64.63 ± 1.79 and 56.00 ± 3.26 kg (p <0.05); daily weight gain of 0.50 ± 0.03 and 0.30 ± 0.04 kg.d-1 (p <0.05); height at weaning of 86.8 ± 0.54 and 84.1 ± 0.89 cm (p <0.05) and daily height gain at weaning of 0.22 ± 0.009 and 0.17 ± 0.01 cm.d-1 (p <0.05), respectively. The calves that received 6 l.d-1had a higher rearing cost (p <0.05). In conclusion, the results show that feeding volumes of whole milk with increasing-decreasing order had a positive impact on the consumption of concentrate, productive performance, and a lower cost of rearing during pre-weaning.

Chemical fertilization has intensified in recent years and one of the biggest concerns is the poor efficiency of the use of nitrogen fertilizers and the environmental costs due to the losses of this element, which has motivated the implementation of low-input systems such as the practice of applying slurry, which can include manure, cleaning waters, rainwater, concentrate residues and litter waste, in order to provide nutrients to the forages that are produced for feeding animals. The objective of this study was to evaluate the quality of the slurry generated at the Alfredo Volio Mata Experiment Station and to determine the effect of its application on the soil and on the productive performance of Taiwan grass (Pennisetum purpureum cv. Taiwan). For the experiment, an area of 225 m2 planted with Taiwan grass was used which was divided into three large blocks and each block was subdivided into three plots that corresponded to the different nitrogen fertilization treatments at an equivalent dose of 300 kg/ha/year distributed in three applications. Each plot was 25 m2 (5 x 5 m). The treatments used were: 1) the control (0 kg of nitrogen), 2) slurry and 3) urea (46% of N). Soil samples were taken to perform an analysis at the beginning and at the end of the experiment, which included chemical-physical and microbiological characterization. The chemical analysis carried out on the slurry reports relatively low values of N, P and K (0.04, 0.01 and 0.04%, respectively). No significant changes were observed in terms of the chemical properties of the soil when comparing the analyzes carried out before and after the application of the different treatments. Regarding yield and nutritional quality of the forage, only statistically significant differences (P<0.05) were found for the percentage of CP where the treatments with urea and slurry presented the highest concentration of CP in the whole plant.

During the years 2012-2017 Multiovulation and Embryo Transfer (MOET) technique was applied in Holstein and Girolando F1 animals at the Animal Reproduction Unit (URA), of the Escuela de Zootecnia of the University of Costa Rica, with the aim to create and evaluate a Girolando herd in the Costa Rican Atlantic. Female embryo donors were selected at external farms and URA. Selection in external farms was done through the information of breed herd books and farm records, while in URA, through the data of lactation and performance of the offspring. In addition, an estimation of partial costs of embryo production was obtained. URA evaluated animals, as part of the embryo donors selection, showed an average daily milk production of 11.1 kg, with an average lactation length of 296 days, on a single daily milking and with a calf at the cow side. The weaning was carried out at 7 months of age, with an average weight of 255 kg (244 kg for females and 262 kg for males). Overall, in both URA and external farms, 38 collections were done in 24 selected donors, from which 381 structures were collected, 73.5% fertilized and 26.5% unfertilized. From those fertilized structures (embryos), 47.3% were considered transferable (quality 1 and 2 according to the International Society of Embryo Transfer, IETS), for an overall average of 4.8 transferable embryos per collection. 83 fresh embryo transfers and 34 frozen embryo transfers were performed, from which 33.7% (28/83) and 5.9% (2/34) pregnancy rates were obtained, respectively. The low pregnancy rates obtained, compared to literature reports, are not normal results, but are related to this particular study. The production cost of an embryo,  due to consumables, hormones and semen was US$62.5 dollars. Production and embryo transfer technique collaborated in the creation and development of the Girolando herd of the Animal Reproduction Unit of the University of Costa Rica.

Aflatoxin B1 (AFB1) is the most toxic and prevalent aflatoxin worldwide, it causes acute aflatoxicosis, has a carcinogenic and cytotoxic effect in animals and humans. AFB1 is a secondary metabolite produced by Aspergillus spp., particularly in tropical and subtropical regions. Generally, cereals are the most significant risk of exposure for animals and are the most widely used in the formulation of feedstuffs for dairy farms. Cows that ingest feedstuffs contaminated with AFB1 excrete aflatoxin M1 (AFM1) through the milk, at a transfer rate from 0.30 to 7.26%. AFM1 has a carcinogenic effect, but is less potent than AFB1. AFM1 is stable to the milk pasteurization processes used in the dairy industry. The consumption of AFM1-contaminated dairy products increases the risk of cancer in humans, making it one of the most important food safety problems. Considering the impact of AFB1/AFM1 on food safety for animals and humans, this paper provides an insight into the relationship between AFB1 and food for dairy cows, the transfer of AFB1 to AFM1 in milk and dairy products, effects on production and reproductive performance in the animal, importance on public health, as well as, the most convenient strategies to control AFB1 and AFM1 levels in dairy industry production chain. Control of the impact of AFB1/AFM1 in dairy farms should include a surveillance and monitoring plan in the farm using reliable analytical techniques, on tank milk samples, on-site that help strengthen feedstuffs control measures to ensure cow welfare and food safety.

Nutritional quality of feeds or ingredients used to feed ruminants depends on the level of intake, rumen degradability, digestibility, nutrient concentration, and the efficiency with which these can be metabolized and used. Once feed is ingested, degradability refers to the amount of feed that disappears in the rumen due to the action of the microorganisms. Rumen degradation is crucial in the supply of dietary nutrients to meet nutrient demands of microorganisms and body tissues of animals. Therefore, it is essential to study the dynamics of rumen degradation of feeds before their potential use to formulate nutritious diets for ruminant animals. Amongst many methods that have been used in the past, the in sacco method has been the most effective to study rumen degradation. However, this method is nowadays used less frequently due to its implications for animal welfare. While many in vitro methods have been tested as possible alternatives to the in sacco method, they were unable to remove the need to use fistulated animals to obtain rumen fluid. Rumen cannulation can be done on a healthy animal currently in the herd with minimal expense. The surgery is not more difficult than most other routine surgical procedures performed by veterinarians. A cannulated animal also provides a long-term, readily available source of rumen content that can be used to transfaunate herd mates that have suffered various digestive upsets. The objective of this work is to present, in a summarized way, the different steps in the fistulation of a cow, and to detail the use of the in vivo or in sacco technique to determine ruminal degradability of feeds or ingredients.