Statistical evaluation of factors and interactions affecting dairy herd improvement milk urea nitrogen in commercial midwest dairy herds.

In this study, 400,729 Dairy Herd Improvement (DHI) records collected on 77,178 cows in 692 Midwest herds over 29 mo (January 1999 to May 2001) were used to analyze milk urea nitrogen (MUN) as collected the day of the test in 6 breeds. Records of Holsteins, Jerseys, and Brown Swiss were subjected to stepwise backward elimination analysis with a model including parity (primiparous vs. multiparous cows), sample type (morning vs. evening), milking frequency (2x vs. 3x [Holstein only]), season (winter, spring, summer, and fall), yield of fat-corrected milk (FCM) classified into 1 of 3 FCM categories (FCMc) and all possible higher-order interactions. Results indicated that FCMc contributed to test-day MUN variation in multiparous, but not primiparous, Holsteins. Sample type and season were significant in both parity groups; milking frequency was not significant, but milking frequency x season and milking frequency x FCMc were significant in both parity groups. The nature of these interactions differed for each parity group. For Jersey and Brown Swiss data analyzed by sample type separately, parity was not significant but tended to interact with FCMc, whereas season, FCMc, and season x FCMc were generally significant. Mean test-day MUN was 12.7, 14.6, and 14.4 mg/dL, with 24, 45, and 42% of records above 14.5 mg/dL in Holsteins, Jerseys, and Brown Swiss in single-breed herds, respectively. In Holsteins, MUN peaked at 7 to 10 d in milk (DIM), declined until 28 to 35 DIM, and rose again thereafter. In primiparous Holsteins, MUN did not change with FCM

Models for predicting dry matter intake of Holsteins during the prefresh transition period.

The objectives of this study were to develop and validate a model for predicting dry matter intake (DMI) of Holsteins during the prefresh transition period. The original database (ODB) for model development was established by compiling parity, body condition score (BCS), and DMI data during the final 3 wk of gestation from 366 Holsteins fed 24 different diets that were used in eight experiments conducted at three universities. For model validation, a validation database (VDB) was established by compiling data from 333 prefresh transition Holsteins fed 25 different diets that were used in eight experiments conducted at five universities. Dry matter intake during the prefresh transition period was fitted to an exponential function: DMI(t) = a + pe(kt), where DMI(t) = DMI as a percentage of body weight (BW) at time t, a = asymptotic intercept at time--infinity, p = change in intake (kg) from the asymptotic intercept until parturition, k = rate constant influencing the shape of the curve, and t = day relative to parturition expressed as days pregnant--280. The model developed from the ODB predicted DMI of heifers in the VDB with satisfactory accuracy and precision. However, this was not true for cows, probably due to differences in BCS of cows and diets fed to cows from the two data sets. When a subset of cows was selected from each data set that had similar BCS (> 4.0) and were fed similar diets, accuracy and precision of the model predicting DMI was improved. Finally, both databases were combined to develop final models for predicting DMI of heifers and cows. Proposed models for predicting mean daily DMI of heifers and cows during the prefresh transition period were DMI(t) = 1.713-0.688e(0.344t) (R2 = 0.96) and DMI(t) = 1.979-0.756e(0.154t) (R2 = 0.97), respectively. Adjustment factors for animal and dietary factors were generated to demonstrate the plausibility of adaptive fitting of the prediction. The regression coefficients of prediction models (a, p, and k) were affected by BCS and dietary organic macronutrient concentrations.

Animal and dietary factors affecting feed intake during the prefresh transition period in Holsteins.

Parity, body condition score (BCS), and dry matter intake (DMI) data of 699 Holsteins fed 49 different diets during the final 3 wk of gestation (prefresh transition period) were compiled from 16 experiments conducted at eight universities. The objectives of this study were to determine the effects of animal and dietary factors on DMI and to elucidate interactions between animal and dietary factors and among dietary factors on DMI during the prefresh transition period. Animal factors examined were parity and BCS, whereas dietary factors examined were rumen undegradable protein (RUP), rumen degradable protein (RDP), neutral detergent fiber (NDF), and ether extract (EE). DMI decreased 32% during the final 3 wk of gestation, and 89% of that decline occurred during the final week of gestation. Day of gestation, animal factors, and dietary factors accounted for 56.1, 19.7, and 24.2% of explained variation in DMI, respectively, and R2 of this linear multivariable model was 0.18. Cows had higher DMI than heifers. DMI decreased linearly as BCS, RUP, and NDF increased, decreased quadratically as EE increased, and increased quadratically as RDP increased. Moreover, the magnitude of DMI depression as animals approached parturition was affected by characteristics of animals and dietary nutrient composition. There were significant parity x EE, BCS x NDF, RUP x NDF, RDP x NDF, NDF x EE, and RUP x EE interactions on DMI. In conclusion, parity, BCS, and concentrations of organic macronutrients in diets affected DMI during the prefresh transition period, and the magnitude of DMI depression as animals approached parturition.

Effects of pubic symphysiodesis in dysplastic puppies.

OBJECTIVE: To determine the long-term effects of juvenile pubic symphysiodesis (JPS) in dysplastic puppies. STUDY DESIGN: Prospective, randomized, clinical trial. ANIMALS: Seven dysplastic Chesapeake Bay retrievers and 2 beagle-crosses (BX1 and 2). METHODS: Five puppies had JPS performed with electrocauterization at 12, 16, 20, 22, and 24 weeks of age, respectively. Two puppies served as controls. BX1 and BX2 were used to obtain biopsies of the symphysis. Hips were evaluated for: pelvic development (transverse computerized tomography for acetabular angle [AA] and dorsal acetabular rim angle [DARA]); laxity [hip extended and stress radiography [distraction index (DI)]); Ortolani maneuver with reduction angles; acetabular coverage (Norberg angles); and function (coxofemoral range of motion, hip pain, and gait analysis by force-plate technique at 44 and 137 weeks of age). RESULTS: The pubis fused prematurely in every puppy that was operated on with the JPS technique. Greater acetabular responses were related to younger ages at surgery. The final mean AA in dogs that had JPS was 25 degrees greater than preoperative values; 40% increased over control. The DARA final mean was 10 degrees, 52% less than preoperative values and 46% less than control. The final mean DI in dogs having JPS was 0.28, 47% improved over preoperative values and 58% better than control. Mean pelvic dimensions in dogs that had JPS were 18% less than control. Gait analyses were normal for all dogs at 137 weeks. No urinary or bowel complications occurred. CONCLUSIONS: Significant ventrolateral acetabular rotation, increased hip coverage, diminished hip laxity, normal pain-free gait, and insignificantly reduced pelvic size occurred after JPS. CLINICAL SIGNIFICANCE: Dysplastic hips in young dogs were significantly improved by JPS.

Comparison of two palpation, four radiographic and three ultrasound methods for early detection of mild to moderate canine hip dysplasia.

Hip joint laxity was evaluated in Golden Retriever (n = 60), Labrador Retriever (n = 23), and Labrador/Golden Retriever mix (n = 24) puppies. Ortolani and Bardens maneuvers, four radiographic measurement indices and three dynamic ultrasonographic measurements were used. Each puppy was evaluated twice; at 6.5 to 9 and 43 to 79 weeks of age. These nine methods were compared for accuracy in predicting the development of canine hip dysplasia with or without degenerative joint disease by a median age of 16 months. The Bardens maneuver was a significant predictor of canine hip dysplasia/+/-degenerative joint disease for Golden Retriever puppies, however, it was not a reliable predictor for the other two breeds. Norberg angle measurements taken with femurs in a neutral position with hips distracted (PennHip position) was a significant predictor of degenerative joint disease in two breeds, but not in Golden Retriever puppies. Ultrasound measurement was a reliable predictor of hip canine hip dysplasia/+/-degenerative joint disease for Labrador/Golden Retriever mix puppies, but was not reliable for the other two breeds. Palpation, radiographic, and ultrasonographic methods of evaluating hip joint laxity in puppies at 6.5 to 9 weeks of age were not consistently reliable for all three breeds in predicting hip dysplasia with or without degenerative joint disease at one year of age. A strong association was found between Norberg angle and degenerative joint disease occurrence, as well as between distraction index (PennHip) and degenerative joint disease occurrence when measured at 52 to 79 weeks of age, but not when measured at 6.5 to 9 weeks of age in these breeds. These results emphasize the difficulty of early detection of mild hip dysplasia in the dog.

Regression Analyses for Evaluating the Influence of Bacillus cereus on Alfalfa Yield Under Variable Disease Intensity.

ABSTRACT We developed and tested regression methods to exploit the variability in disease inherent in field experiments, and applied the methods to evaluate strains of Bacillus cereus for biocontrol efficacy. Four B. cereus strains were tested for their effect on alfalfa (Medicago sativa) performance in 16 field trials planted during 1993 to 1996 at multiple sites in Wisconsin. To evaluate performance of the strains, we used the ratio of (metalaxyl response)/(untreated control response) as a measure of disease intensity within the experiments. The ratio of (Bacillus response)/(untreated control response) was then regressed as a function of disease intensity. The slope of the resulting line provides a statistical test to compare performance of the Bacillus strain with that of the untreated seed (H(o): slope = 0) and metalaxyl controls (H(o): slope = 1). Under conditions in which disease occurred, forage yield of plots planted with seed treated with B. cereus strain AS4-12 exceeded yield from the untreated control plots (P = 0.002) and was similar to yield of plots planted with metalaxyl-treated seed (P = 0.14). Yield gain associated with AS4-12 and metalaxyl seed treatment averaged 6.1 +/- 2.8% (+/-standard error) and 3.0 +/- 2.8%, respectively. In contrast to the regression approach, means analysis by analysis of variance did not detect differences among treatments. Three other B. cereus strains either did not increase alfalfa yield or increased yield less than did AS4-12. Metalaxyl and three of the Bacillus strains increased seedling emergence, but the improved stands were not predictive of increased forage yield. In six additional studies conducted for one season in 1997, AS4-12 enhanced yield of two cultivars at diverse locations in Wisconsin, but there was an apparent cultivar-location interaction. A strong correlation between response to AS4-12 and metalaxyl treatment suggests that these treatments controlled similar pathogens, most likely the oomycete pathogens Phytophthora medicaginis and Pythium spp.

The relative effect of dietary energy density on repleted and resting muscle glycogen concentrations.

The aim of this study was to assess the effect of dietary energy density on the glycogen concentration of bovine gluteus medius (GM) and longissimus thoracis et lumborum (LTL) muscles in castrated and intact males. Cattle received diet C (90% whole corn and supplement: 10% alfalfa haylage) or diet AH (100% alfalfa haylage) in three experiments involving a 2×2 factorial cross-over design. Cattle fed an AH diet for 70 days prior to the first experiment had high glycogen concentrations in the GM (129±9.9 mmol/kg) and LTL (108±7.6 mmol/kg) at the first biopsy session. These concentrations are similar to GM (133±6.2 mmol/kg) and LTL (105±5.8 mmol/kg) glycogen concentrations when these cattle subsequently received diet C for 30 or 37 days. Diet C increased muscle glycogen concentration, but the consistency of the increase in glycogen was dependent on the initial concentration. When the initial glycogen concentration was depleted to 50 µmol/g with one subcutaneous injection of adrenaline, repleted glycogen concentration was higher for diet C than AH (P<0.01) in all comparisons involving GM and LTL muscles of both steers and bulls. For resting muscle glycogen, the GM of bulls was more sensitive to the effect of diet C than the bull LTL or either muscle in steers. Diet was not a major determinant of resting muscle glycogen concentration. The ultimate pHs of GM, LTL and semimembranosus (SM) were not affected by diet and residual glycogen was lower in LTL of bulls fed either diet than for LTL of steers fed AH. Diet and male status did not affect residual glycogen in GM or SM.

Quantitative imaging and statistical analysis of fluorescence in situ hybridization (FISH) of Aureobasidium pullulans.

Image and multifactorial statistical analyses were used to evaluate the intensity of fluorescence signal from cells of three strains of A. pullulans and one strain of Rhodosporidium toruloides, as an outgroup, hybridized with either a universal or an A. pullulans 18S rRNA oligonucleotide probe in direct or indirect FISH reactions. In general, type of fixation (paraformaldehyde or methanol-acetic acid) had no apparent effect on cell integrity and minimal impact on fluorescence. Permeabilization by enzyme treatment for various times, though needed to admit high Mw detection reagents (avidin-FITC) in indirect FISH, tended to nonspecifically degrade cells and lower the signal. Digestion was unnecessary and undesirable for the directly labelled probes. Multilabelled (five fluorescein molecules) probes enhanced fluorescence about fourfold over unilabelled probes. Overall, direct FISH was preferable to indirect FISH and is recommended especially for studies of microbes on natural substrata.

A study of deleterious gene structure in plants using Markov chain Monte Carlo.

The characteristics of deleterious genes have been of great interest in both theory and practice in genetics. Because of the complex genetic mechanism of these deleterious genes, most current studies try to estimate the overall magnitude of mortality effects on a population, which is characterized classically by the number of lethal equivalents. This number is a combination of several parameters, each of which has a distinct biological effect on genetic mortality. In conservation and breeding programs, it is important to be able to distinguish among different combinations of these parameters that lead to the same number of lethal equivalents, such as a large number of mildly deleterious genes or a few lethal genes, The ability to distinguish such parameter combinations requires more than one generation of mating. We propose a model for survival data from a two-generation mating experiment on the plant species Brassica rapa, and we enable inference with Markov chain Monte Carlo. This computational strategy is effective because a vast amount of missing genotype information must be accounted for. In addition to the lethal equivalents, the two-generation data provide separate information on the average intensity of mortality and the average number of deleterious genes carried by an individual. In our Markov chain Monte Carlo algorithm, we use a vector proposal distribution to overcome inefficiency of a single-site Gibbs sampler. Information about environmental effects is obtained from an outcrossing experiment conducted in parallel with the two-generation mating experiments.

Early detection of canine hip dysplasia: comparison of two palpation and five radiographic methods.

Hip joint laxity was evaluated in four breeds (i.e., greyhound, Labrador retriever, Irish setter, hound mixed-breed) of puppies (n=32) by Ortolani's and Bardens' maneuvers, by subjective assessment of radiographs (Orthopedic Foundation for Animals [OFA] method), and by four radiographic measurement indices. Puppies were studied at four, six-to-10, 16-to-18, and 52 weeks of age. The purpose of this study was to compare palpation and radiographic methods of hip laxity detection in puppies for predicting the development of degenerative joint disease (DJD) by one year of age. Twenty-seven (42%) hips developed DJD. Ortolani's method was not a reliable predictor of hip dysplasia at six-to-10 weeks; it was significantly predictive at 16-to-18 weeks but had a high incidence of false negatives. Bardens' and subjective (OFA) assessment methods were not reliable at six-to-10 or 16-to-18 weeks. Radiographic measurements taken with femurs in a neutral position and hips distracted (distraction index [DI] and Norberg angle) and measurements taken with femurs extended in OFA position (Norberg angle) of six- to 10-week-old puppies accurately predicted DJD occurrence by one year of age (p less than 0.01). Distraction index measurement (PennHIP method) was the most accurate in predicting the development of DJD (p less than 0.001). Distraction index radiography in puppies six-to-10 and 16-to-18 weeks of age was the most reliable predictor of hip dysplasia. Norberg angle measurement was more reliable during hip distraction than when hips were measured in the OFA position in 16- to 18-week-old puppies, but had similar reliability in six- to 10-week-old puppies.

Number of lethal equivalents in human populations: how good are the previous estimates?

Lee et al. (1996) recently developed a method for interval estimation of the number of lethal equivalents by using a hierarchical structure of likelihood functions. This hierarchical model consists of two multinomial trials: one of the sampling process of the parents from the population of interest, and the other for the survival of the offspring of the families obtained by mating the parents. The method, initially developed for selfing and full-sib mating, is extended here to include more general mating systems as well as mixtures of mating systems. We applied it to human data sets for which confidence intervals were previously not available. Our point estimates were close to previous ones, and the standard deviations were generally quite small. Thus, even if debate over the meaning of the concept of lethal equivalents has not been entirely resolved, our results showed that the previous estimates are at least statistically meaningful.

Modelling age-specific survival in nesting studies, using a general approach for doubly-censored and truncated data.

In typical nest survival studies, the observed sample of nests is usually biased by left-truncation (i.e., only active nests enter the study); additionally the failure data may be doubly censored, because the exact dates of nest initiation and failure are uncertain. We present a general bivariate contingency table approach for analyzing such data. We use weakly structured step spline hazard models, which avoid estimability problems encountered in a strictly nonparametric approach, yet still permit flexibility. Our method eliminates a potential source of bias noted by Heisey and Nordheim (1990, Biometrics 46, 855-862) in the nest survival method of Pollock and Cornelius (1988, Biometrics 44, 397-404). We compare our approach to related techniques developed for estimating the incubation distribution of AIDS.

The effectiveness of examining early post-mortem musculature to predict ultimate pork quality.

Variations in pork quality reflect value differentials. However, only when they can be easily, accurately, rapidly and cost-effectively detected, can swine producers expect to eliminate poor quality from their herds through genetic selection, and can the industry be expected to take the necessary environmental precautions to prevent poor quality. This study was designed to assess the effectiveness of various techniques thought to predict ultimate pork quality through the examination of the physical and chemical properties of early post-mortem (PM) musculature. Based on stiffness and pH 30, 285 carcasses were selected. This selection procedure ensured a wide variation in ultimate quality. Using 12 instruments simultaneously, temperature, stiffness, electrical properties, lightness properties, and pH 45 of the early PM longissimus thoracis et lumborum were recorded to predict ultimate quality. Based on post-rigor light reflection and water-holding capacity (WHC), quality was assigned to one of five arbitrary groups. Of all techniques tested, the only one with any potential for adequate prediction of quality categories was pH 45. Combination of different techniques did not significantly increase predictive values. For predicting quality of single carcasses, pH 45 should not be considered satisfactory. However, based on our success in selecting carcasses representing quality variation for this study and the results obtained from the study, using pH 45 and muscle stiffness to select groups of carcasses is feasible. We conclude that the techniques used early post mortem are not appropriate for predicting ultimate pork quality for single carcasses. At present we recommend that only post-rigor muscle be considered, and that ultimate pH, light reflection and a measure of WHC should be used.

Microbial community analysis in incompletely or destructively sampled systems.

Analyses of microbial community dynamics are often constrained by the destructive, indirect, and incomplete nature of most sampling techniques. These methodological constraints compel assumptions that are rarely verified about the relationships among separate communities. We evaluated the consequences for community analysis of the common assumption that separate microbial communities are described by the same species abundance distribution. Sample data were generated from simulated communities in which the species abundance distributions were the same or were different. Samples from communities that had the same number of species or were described by the same species abundance distribution sometimes had significantly different numbers of species. Samples from simulated communities that had different species number-species abundance distribution combinations sometimes contained indistinguishable numbers of species. When sampling from independent communities described by unknown distributions (e.g., microbial communities on plant surfaces), the simulations showed that standardization of sample size (number of individuals or colony-forming units) does not guarantee samples of equal proportions of the total species in a community. Sample sizes that are logistically feasible for many microbial systems will provide only limited information for differentiating species numbers or species abundance distributions among separate communities over time. For ecologists studying destructively or incompletely sampled communities this seriously influences both the sample designs that are reasonable and the questions that can be addressed in such systems.

The estimation of parameters from bulked samples.

An estimation procedure has been developed for the estimation of parameters from bulked sample using the parametric bootstrap and density estimation in conjunction with the one-step maximum-likelihood estimator. It is shown that the proposed estimation procedure provides an asymptotically efficient estimator for parameters of interest when the density for the mean of the bulked samples has a certain form. The lognormal density (with sigma 2 assumed known) is an important distribution with the proper form. The finite sample performance for bulked samples based on underlying lognormal observations was examined by Monte Carlo study. The results indicate that the proposed procedure leads to a reduction in mean squared error compared to known procedures.

Experimental model of hypochloremic metabolic alkalosis caused by diversion of abomasal outflow in sheep.

Hypochloremic metabolic alkalosis accompanied by hypokalemia and hyponatremia was induced experimentally in 7 adult sheep by diversion (loss) of gastric contents through an Ivan and Johnston cannula placed in the cranial part of the duodenum just distal to the pylorus. Cannula placement was easily accomplished, and cannulae were tolerated well by the sheep. Volume of effluent produced during the 60- to 120-hour period of diversion ranged from 7.7 to 14.9 L and tended to be greatest during the first 24 hours. All sheep became dehydrated, with mean PCV and plasma total protein concentration increases of 94.2 and 61.7%, respectively. Plasma chloride concentration decreased in linear fashion from a prediversion mean of 113 mEq/L (range, 111 to 117 mEq/L) to an end-point mean of 54 mEq/L (range, 45 to 65 mEq/L). Plasma sodium and potassium concentrations also decreased, though potassium concentration increased terminally. There were rapid increases in arterial blood pH and bicarbonate and base excess concentrations during the first 48 hours after diversion. However, during the final stages of diversion, sheep developed superimposed metabolic acidosis with increased plasma lactate concentration and high anion gap.

Effects of ketamine, xylazine, and a combination of ketamine and xylazine in Pekin ducks.

Effects of ketamine, xylazine, and a combination of ketamine and xylazine were studied in 12 male Pekin ducks (7 to 12 weeks old; mean [+/- SD] body weight, 3.1 +/- 0.3 kg). After venous and arterial catheterization and fixation of a temperature probe in the cloaca, each awake duck was confined, but not restrained, in an open box in a dimly lit room. Blood pressure and lead-II ECG were recorded. Three arterial blood samples were collected every 15 minutes over a 45-minute period (control period) and were analyzed for pHa, PaCO2 and PaO2. After the control period, each duck was assigned at random to 1 of 3 drug groups: (1) ketamine (KET; 20 mg/kg of body weight, IV), (2) xylazine (XYL; 1 mg/kg, IV), and (3) KET + XYL (KET 20 mg/kg and XYL, 1 mg/kg; IV). Measurements were made at 1, 5, 10, 15, 30, 45, 60, and 90 minutes after drug administration. All ducks survived the drug study. Cloacal temperature was significantly (P less than or equal to 0.05) increased above control cloacal temperature at 90 minutes after the administration of ketamine, and from 10 through 90 minutes after administration of ketamine plus xylazine. In ducks of the KET group, pHa, PaCO2, and PaO2, remained unchanged after administration of the drug. In ducks of the XYL group, pHa and PaO2 decreased significantly (P less than or equal to 0.05) from control values for all time points up to and including 15 minutes after drug administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Fungal immigration dynamics and community development on apple leaves.

Fungal immigration dynamics and community development were followed over time on sets of surface-disinfested apple leaves in the field. Immigration was defined as the arrival of viable propagules on the leaf surface. In three separate experiments (May, June, July), total numbers of fungal immigrants, numbers of filamentous fungal immigrants, and numbers of yeast immigrants per leaf were estimated for successive 12-hour immigration periods. Communities developing over 2-14 immigration periods (1-7 days) were compared with the corresponding estimates of cumulative immigration. There were significant differences among both experiments and immigration periods within each experiment in mean numbers of immigrants per leaf. Leaf area was often significantly correlated with numbers of immigrants. Developing communities supported progressively fewer individuals than the corresponding sums of immigrants, suggesting that losses due to emigration and/or death play a critical role in shaping these communities.

Microbial introductions to apple leaves: Influences of altered immigration on fungal community dynamics.

Fungal immigration to apple leaves in the field was altered by the introduction of populations ofChaetomium globosum orAureobasidium pullulans to surface-disinfested leaves either immediately following, or 6 days after, disinfestation. Total numbers of fungal individuals and numbers of filamentous fungal and yeast individuals were estimated and compared over time for 4-7 weeks on control leaves (leaves disinfested but no populations applied), onAureobasidium-treated, and onChaetomium-treated leaves. Fungal communities developing on leaves during three experiments in two different time frames (experiment 1: July 9-August 27; experiments 2 and 3: July 29-August 27), and thus under different immigration regimes, were also compared. Survival of introduced populations was not related to the presence of prior fungal immigrants. Rates of increase in total numbers of fungi and numbers of filamentous fungi and yeasts per leaf varied among experiments, apparently in relation to differences in immigration and environmental history. Differences among leaves in immigration had a short-term (days) influence on community size. However, no long-term effects of altered immigration on phylloplane fungal community size were evident.

Experimental respiratory decompression sickness in sheep.

Respiratory decompression sickness (RDCS, "the chokes") is a potentially lethal consequence of ambient pressure reduction. Lack of a clearly suitable animal model has impeded understanding of this condition. RDCS, unaccompanied by central nervous system signs, occurred in 17 of 18 unanesthetized sheep exposed to compressed air at 230 kPa (2.27 ATA) for 22 h, returned to normal pressure for approximately 40 min, and taken to simulated altitude (0.75 ATA, 570 Torr). Respiratory signs, including tachypnea, sporadic apnea, and labored breathing, were accompanied by precordial Doppler ultrasound evidence of marked venous bubble loading. Pulmonary arterial pressures exceeded 30 Torr in five catheterized sheep that died or became moribund. Hypoxemia (arterial Po2 less than 40 Torr), neutropenia, and thrombocytopenia were observed. Peribronchovascular edema was the most prominent necropsy finding. Chest radiography indicated interstitial edema in most affected sheep. High body weight and catheterization predisposed the sheep to severe RDCS. It appears that this protocol reliably provides a useful animal model for studies of RDCS and obstructive pulmonary hypertension, that the precipitating event is massive pulmonary embolization by bubbles, and that venous bubbles, detected by Doppler ultrasound, can signal impending RDCS.