Scale of Patchiness Affects the Relation Between Forage Quality and Patch Choice by Cattle

We predicted and tested the effects of scale of heterogeneity on movements and selectivity of a large grazer in a controlled field experiment. We created random mosaics of short/high quality and tall/low quality grass patches in equal proportion at grid sizes of 2x2 m and 5x5 m. Subsequently, we monitored the foraging behavior of four steers in 16 20x40 m plots over 30-minute periods. As predicted, the animals selected the short patches both by walking in a nonrandom manner and by concentrating their grazing time. Selectivity was more pronounced in large patches than in small ones. In contrast, the number of bites per feeding station was not affected by patch size, suggesting that selection between and within feeding stations are essentially different processes. We conclude that selectivity is facilitated by large scale heterogeneity, particularly by enhancing discrimination between feeding stations and larger selection units

Cospectral analysis of high frequency signal loss in eddy covariance measurements

International audienceThe cospectra of momentum (M), sensible heat (H), latent heat (LE), and carbon dioxide (Fc) fluxes measured by eddy covariance (EC) over a shortgrass steppe are calculated for over 800 time intervals spanning a range of wind, surface heating, evaporative, and photosynthetic conditions. The power spectrum of the vertical wind clearly shows that the inertial subrange is not sufficiently captured. The cospectra of the different fluxes show that the lack of measurement resolution in the high frequency results in a loss of flux, especially as stability approaches neutral. A procedure is outlined to use statistics from the cospectrum to estimate the amount of high-frequency flux that remains unmeasured for each time interval. The greatest loss of flux was for H (14% on average for 0>z/L>0.001 where z/L is the dimensionless stability), consistent with other studies which indicate temperature fluctuations actively produce turbulence at high frequencies. LE and Fc showed less than half as much loss of flux as H. This differential loss of flux has direct implications for addressing energy balance closure in EC studies, as well as reconciling biases of fluxes measured by EC with the Modified Bowen Ratio technique. It is recommended that the cospectra of fluxes be examined while setting the height of instrumentation in order to insure that high frequency eddies are resolved

Can social interactions affect food searching efficiency of cattle?

Experienced members of a herd of cattle, referred to as social models in this paper, may play an important part in the searching pattern of naive animals. Naive animals may distribute themselves more evenly because their expectations of preferred areas are not as developed as the expectations of experienced animals. We tested three treatments to investigate if social models tend to transmit information about places of grazing to naive ones or if food distribution tends to be more uniform when animals have less experience with the area. A fenced paddock with 192 trays spaced at about 5 m apart was used to conduct this experiment. Treatment one was the clumped distribution treatment (CDT). Food trays were placed as sets of four. Treatment two was the scattered distribution treatment (SDT). Food trays were placed evenly covering different areas of the paddock. In these two treatments, steers were allowed to find 32 trays with feed in the presence of a social model. Treatment three is a control (CT). Steers were allowed to find 32 trays containing feed with no social model present. The experiment lasted seven days and starting on day four, CDT had a higher FL/NL (ratio of found locations to new locations) than CT (P<0.05). This suggests that naive animals tend to be more efficient in finding preferred food locations in the presence of an experienced model. CDT had a higher FLNL than SDT on days three, six and seven of the experiment (P<0.05). This suggests that the initial distribution of food affected the searching efficiency of naive animals. Moreover, within three days steers in all three treatments did better than expected by chance in locating food. Key words: Grazing, searching, distribution, spatial memor

MODELING EXTENSIVE LIVESTOCK PRODUCTION SYSTEMS: AN APPLICATION TO SHEEP PRODUCTION IN KAZAKHSTAN

A stochastic dynamic programming model for extensive livestock systems is developed. The model optimizes sales/retention decisions when future forage production, which affects animal performance and hence profitability, is uncertain. The model is applied to sheep production in Kazakhstan to evaluate policy alternatives.Livestock Production/Industries,

Differential Responses of Yield and Shoot Traits of Five Tropical Grasses to N and Distance to Trees in Silvopastoral Systems

Light intensity and nitrogen (N) availability are important factors influencing the growth of C4 forage species. Trade-offs may occur in the adaptive responses of species to shading and N inputs, and functional shoot traits can help to explain the consequences of these responses for species performance. Our objective was to gain understanding of the mechanisms between traits of five C4 perennial grasses determining above-ground dry matter yield (DMY) when both resources, light and N, vary. Forage grasses were grown in six shading conditions (full sunlight vs. five positions between Eucalyptus dunnii rows) with two N levels (0 vs. 300 kg N ha-1year-1) and clipped when the canopy reached 95% light interception. Path analysis was used to explore the relationship between DMY, shading levels, N nutrition index and shoot traits. Dry matter yield increased between 126 to 569 g dry matter m-2 with N fertilization. Nitrogen nutrition index was the most important predictor for determining DMY followed by shading level. Increased shading reduced DMY by 9.5 g DM m- ² for each 1% of increase in shading. DMY was also modulated by shoot traits such as specific leaf area and leaf area index, but with different responses according to species, highlighting different strategies to cope with changes in light and N availability

Violence perception in Mexico related to subjective and social well-being

El presente estudio evalúa las actitudes hacia la violencia social en México y las contrasta con medidas de satisfacción como son; el bienestar subjetivo desde la perspectiva cognitiva de satisfacción con la vida (Diener, 1980) y el bienestar social (Keyes, 1998). Para evaluar las actitudes frente a la violencia social, exploramos la Escala de Actitudes ante la Violencia Social (Navarro, 2010). Muestra de 101 participantes (77 M, 24 H) del estado de Colima, México. Las tres subescalas de las Actitudes ante la Violencia Social muestran consistencia interna y correlacionan de manera negativa en relación al Bienestar Subjetivo y Bienestar Social. Los resultados indican efectos negativos generados por la percepción de violencia pero sobre todo incongruencia entre una elevada alarma social ante la violencia y una relativamente baja reacción conductual. Las medias en satisfacción con la vida y en las subescalas de bienestar social son relativamente elevadas como se viene observando en estudios anteriores sobre estos constructos en la población mexicana.The present study evaluates attitudes towards social violence in Mexico and contrasts them with satisfaction measures, such as; satisfaction with life (Diener, 1980) and social well-being (Keyes, 1998). To evaluate attitudes originated from violence we explored the attitudes towards social violence scale (Navarro, 2010). Sample 101 subjects (77 W, 24 M) residents of the state of Colima, Mexico. The three subscales composing the attitudes originated from social violence scale show internal consistence and correlate negatively to subjective and social well-being. These results indicate some negative effects of attitudes originated from violence. There is no congruence between high social alarm and low behavioral responses. Satisfaction with life and social well-being are relatively high as usual in Mexican population

Diffusion and Inhibition Processes in a Hollow-fiber Membrane Bioreactor for Hybridoma Culture. Development of a Mathematical Model

The performance of a hollow-fiber membrane bioreactor (HFBR) (molecular weight cut-off 30 kD, fiber surface area 2050 cm2) containing a culture of hybridoma cells has been investigated. Experimental data were used as basis to develop a model of general application. Concentrations of fundamental nutrients (glucose and glutamine), inhibitory products (ammonium and lactate), and monoclonal antibodies (MAb) against bovine lactoferrin (IgG1) were monitored over time. Exchange of nutrients and products occurred across the capillary surface, whereas cells and MAb remained in the extra-capillary space (ECS). A protein-free culture medium (Hybrimax) with and without antibiotics was used. In both cases, the final MAb concentration was the same; however, antibiotic presence slowed down the time to achieve this concentration. Diffusion assays have been carried out in order to support the development of a mathematical model that describes the performance of the HFBR, including mass transfer and reaction terms. Inhibition by ammonium and lactate has been considered in the kinetics, providing model results consistent with experimental data. Further research with other cell lines and/or culture media will allow to broaden the field of application of this model for general use in HFBR systems

Rich Information in the Acoustic Signals from Feeding and Grazing in Ruminants

Because of their impact on productivity and the environment, feeding behaviour, ingestion and rumination are critical to understand intake in grazing ruminants. Many systems, mainly mechanical, have been developed to measure ingestive behaviour. However, these systems have problems, including mechanical failure and the inability to distinguish between the complex jaw movements of prehension and ingestion (Laca et al., 1994). The sounds generated by these behaviours are rich in information that holds potential not only to distinguish and count behaviours, but also identify aspects of the nature of the foods ingested

Bayesian hierarchical models to improve estimation of diet composition by alkane profiles.

Alkane profiles in forage and feces are used to determine diet composition, essentially by inverting a linear mixing equation. Depending on the number of dietary components, number of alkanes and difference in forage profiles, the linear equations can be over or underdetermined. We compared the typical non-negative least squares (NNLS) method against a novel Bayesian hierarchical model (BHM) where diet composition is represented as latent variables modeled with parameters shared by the models for fecal and forage profiles. Forage and fecal profiles were obtained from steers grazing either Brachiaria brizantha cv Marandu, Panicum maximum cv. Mombaça, or Pennisetum purpureum cv. Cameroon at Embrapa Beef Cattle, Campo Grande, MS, Brazil. Herbage and fecal samples were collected in the dry and early wet seasons. Herbage was sampled by 20-cm horizons sorted into stem/sheath and leaf blade as dietary components. Feces were collected from 6 animals in the morning and afternoon. Fecal profiles were corrected by faecal recoveries using mean values from the literature. Distributions of diets estimated by NNLS were obtained by Monte Carlo simulation of profiles using parameters and covariance matrices estimated from data. The BHM yielded posterior distributions directly by using Monte Carlo Markov Chains. NNLS resulted in highly variables diets with distributions that were clearly non-normal. BHM resulted in quasi-normal posterior distributions. We conclude that both approaches are better than the normal approach where diet covariances are calculated ad-hoc. The BHM method has the potential to be vastly superior because it allows the simultaneous integration in a formally correct manner, however, convergence can be difficult

The Sound of Chewing

Acoustic biotelemetry has been proposed as a way to count ingestive bites and chews of grazing animals. Recent work has indicated the possibility that detailed analysis of \u27sounds of chewing\u27 contains information about other characteristics of the ingestive process that can be used to study grazing behaviour of free ranging animals (Laca & Wallis DeVries, 2000), or to monitor stall-fed animals in more detail