Evaluation of gastrointestinal activity patterns in healthy horses using B mode and Doppler ultrasonography

Healthy adult horses were examined by using transabdominal ultrasonography to quantitatively and qualitatively evaluate activity of the jejunum, cecum, and colon with B mode and Doppler techniques. Doppler ultrasound was used to assess jejunal peristaltic activity. Examinations were performed on multiple occasions under imposed colic evaluation conditions, including fasting, nasogastric intubation, and xylazine sedation. In fasted horses, jejunal visibility was increased and jejunal, cecal, and colonic activity was decreased. The stomach was displaced ventrally and was visualized ventral to the costochondral junction. Xylazine sedation in fed horses had minimal effects; however, in fasted horses, xylazine significantly decreased jejunal and cecal activity. Nasogastric intubation in fasted horses had no observable effects on activity, but moved the stomach dorsally. B mode and Doppler jejunal activity were strongly correlated. Prior feeding and sedation status need to be considered when interpreting the results of equine abdominal ultrasound examinations. Doppler techniques may be useful for assessing jejunal activity.     

Modeling hydrology, metribuzin degradation and metribuzin transport in macroporous tilled and no-till silt loam soil using RZWQM

Due to the complex nature of pesticide transport, process-based models can be difficult to use. For example, pesticide transport can be effected by macropore flow, and can be further complicated by sorption, desorption and degradation occurring at different rates in different soil compartments. We have used the Root Zone Water Quality Model (RZWQM) to investigate these phenomena with field data that included two management conditions (till and no-till) and metribuzin concentrations in percolate, runoff and soil. Metribuzin degradation and transport were simulated using three pesticide sorption models available in RZWQM: (a) instantaneous equilibrium-only (EO); (b) equilibrium-kinetic (EK, includes sites with slow desorption and no degradation); (c) equilibrium-bound (EB, includes irreversibly bound sites with relatively slow degradation). Site-specific RZWQM input included water retention curves from four soil depths, saturated hydraulic conductivity from four soil depths and the metribuzin partition coefficient. The calibrated parameters were macropore radius, surface crust saturated hydraulic conductivity, kinetic parameters, irreversible binding parameters and metribuzin half-life. The results indicate that (1) simulated metribuzin persistence was more accurate using the EK (root mean square error, RMSE = 0.03 kg ha(-1)) and EB (RMSE = 0.03 kg ha(-1)) sorption models compared to the EO (RMSE = 0.08 kg ha(-1)) model because of slowing metribuzin degradation rate with time and (2) simulating macropore flow resulted in prediction of metribuzin transport in percolate over the simulation period within a factor of two of that observed using all three pesticide sorption models. Moreover, little difference in simulated daily transport was observed between the three pesticide sorption models, except that the EB model substantially under-predicted metribuzin transport in runoff and percolate >30 days after application when transported concentrations were relatively low. This suggests that when macropore flow and hydrology are accurately simulated, metribuzin transport in the field may be adequately simulated using a relatively simple, equilibrium-only pesticide model.     

Application of the Root Zone Water Quality Model (RZWQM) to pesticide fate and transport: an overview

Pesticide transport models are tools used to develop improved pesticide management strategies, study pesticide processes under different conditions (management, soils, climates, etc) and illuminate aspects of a system in need of more field or laboratory study. This paper briefly overviews RZWQM history and distinguishing features, overviews key RZWQM components and reviews RZWQM validation studies. RZWQM is a physically based agricultural systems model that includes sub-models to simulate: infiltration, runoff, water distribution and chemical movement in the soil; macropore flow and chemical movement through macropores; evapotranspiration (ET); heat transport; plant growth; organic matter/nitrogen cycling; pesticide processes; chemical transfer to runoff; and the effect of agricultural management practices on these processes. Research to date shows that if key input parameters are calibrated, RZWQM can adequately simulate the processes involved with pesticide transport (ET, soil-water content, percolation and runoff, plant growth and pesticide fate). A review of the validation studies revealed that (1) accurate parameterization of restricting soil layers (low permeability horizons) may improve simulated soil-water content; (2) simulating pesticide sorption kinetics may improve simulated soil pesticide concentration with time (persistence) and depth and (3) calibrating the pesticide half-life is generally necessary for accurate pesticide persistence simulations. This overview/review provides insight into the processes involved with the RZWQM pesticide component and helps identify model weaknesses, model strengths and successful modeling strategies.     

Documenting the pesticide processes module of the ARS RZWQM agroecosystem model

We describe the theory and current development state of the pesticide process module of the USDA-Agricultural Research Service Root Zone Water Quality Model, or RZWQM. Several processes which are significant in determining the fate of a pesticide application are included together in this module for the first time, including application technique, root uptake, ionic dissociation, soil depth dependence of persistence, volatilization, wicking upward in soil and aging of residues. The pesticide module requires a large number of parameters to run (as does the RZWQM model as a whole) and it is becoming clear that RZWQM will find most interest and use as part of a 'scenario' in which all data requirements are supplied and the predictions of the system compared with a real (usually partial) data set. Such a scenario may then be modified to examine the response of the system to changes in inputs. It also has significant potential as a technology transfer or teaching tool, providing detailed understanding of a specific agronomic system and its potential impacts on the environment.     

Severe carpometacarpal osteoarthritis in older Arabian horses

OBJECTIVE: To report a severe form of carpometacarpal osteoarthritis (CMC-OA) affecting primarily older Arabian horses. STUDY DESIGN: Retrospective study. ANIMALS: Thirty-one horses with CMC-OA. METHODS: Carpal radiographs (405 sets) from 3 hospitals were evaluated to identify horses with marked osteoproliferative reaction across the medial aspect of the CMC joint. Owners were contacted to obtain detailed histories and status updates. Necropsy specimens of the CMC joint were evaluated at 2 hospitals to determine the prevalence of 2 variations in the articulation between the proximal second and third metacarpal bones. RESULTS: Thirty-one horses were identified as having marked osteoproliferative reaction at the CMC joint. Twenty-three (74%) were Arabian horses. Of the Arabian horses, the average age at admission was 14.4 years. Eight (34.8%) Arabian horses had a known history of trauma. Most were no longer rideable at presentation. Ten of the horses were subsequently euthanatized because of lameness. The dorsal and palmar articulations between the second and third metacarpal bones were examined in 177 horses. The palmar articulation was absent in 48% of Arabian horses and 12.5% of non-Arabian horses at 1 center, including 4 horses with CMC-OA. At the second center, the palmar articulation was present in 8 of 8 Arabian horses but was absent in 22 of 92 (24%) non-Arabian horses. CONCLUSIONS: An increased frequency of this crippling form of OA was observed in Arabian horses. It may reflect an increased prevalence, in some geographical regions, of an absent palmar articulation between the second and third metacarpal bones. CLINICAL RELEVANCE: Carpal trauma in some Arabian horses may result in unexpectedly severe carpometacarpal osteoarthritis.