Effects of pulmonary abscesses on racing performance of horses treated at referral veterinary medical teaching hospitals: 45 cases (1985-1997).

OBJECTIVE: To determine whether results of physical or radiographic examination or biochemical analyses in adult racehorses with primary lung abscesses were associated with ability to race following treatment. DESIGN: Multiple-center retrospective study. ANIMALS: 25 Standardbreds and 20 Thoroughbreds. PROCEDURE: Medical records of horses with a primary lung abscess that were admitted to any of 4 veterinary teaching hospitals were reviewed. Results of physical examination, laboratory testing, and thoracic radiography were reviewed. Racing performance after treatment was compared with performance before illness and with performance of the general population of racehorses of similar age, sex, and breed. RESULTS: 23 of 25 Standardbreds and 13 of 20 Thoroughbreds raced after diagnosis and treatment of a lung abscess. Most horses had a solitary abscess in the dorsal to caudodorsal lung fields. Results of initial physical examination, biochemical analyses, and culture and identification of the microbial isolate were not associated with whether a horse returned to racing. For horses that had raced prior to the illness, race performance after treatment of the lung abscess was not significantly different from performance before the illness. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of racing performance in those horses that resumed racing after treatment, long-term residual lung damage did not develop in horses with primary lung abscesses that were treated appropriately. It is not known whether horses that recovered would be more likely to bleed from the site of a prior infection when resuming strenuous exercise and whether lung abscesses contributed to a failure to resume racing.

Analysis of correlated continuous repeated observations: modelling the effect of ketosis on milk yield in dairy cows.

This study used mixed models analysis to demonstrate the advantages of a repeated measures technique for a continuous variable over a single measure technique. As an illustration, the loss of milk yield due to ketosis was studied in 2604 multiparous New York State Holstein cows belonging to eight herds, calving between 1991 and 1993. Two methods of analysis were presented: The first treated milk yield as a continuous, summary measure (projected 305-day milk yield); the second treated milk yield as repeated measurements (test-day milk yields). In the first example, with 305-day milk yield as the outcome, ketosis was treated as a binary covariate. Ketosis had no effect on the 305-day milk yield. In the second example, with monthly test-day milk yields as the outcome, four different covariance structures (simple, compound symmetry, autoregressive, and unstructured) to model the association among the repeated measurements were compared. With this approach, ketotic cows yielded significantly less milk per day both before and immediately after diagnosis than did non-ketotic cows. Based on the goodness-of-fit statistics, it was unclear whether an autoregressive or unstructured covariance structure was best. However, an autoregressive structure, in which the previous and current test-day milk yields are assumed to be correlated, was considered more suitable in this study; it is a simpler and more appropriate covariance structure for this particular problem than is an unstructured covariance structure. Nevertheless, with the test-day approach, any of these correlation structures could be used to estimate milk loss after disease. Based on these findings, it is recommended that a repeated measures approach, rather than a single measure approach, be used to study the short-term effect of disease on milk yield.

Associations between physical examination, laboratory, and radiographic findings and outcome and subsequent racing performance of foals with Rhodococcus equi infection: 115 cases (1984-1992).

OBJECTIVE: To determine whether physical examination, laboratory, or radiographic abnormalities in foals with Rhodococcus equi infection were associated with survival, ability to race at least once after recovery, or, for foals that survived and went on to race, subsequent racing performance. DESIGN: Retrospective study. ANIMALS: 49 Thoroughbreds and 66 Standardbreds admitted to 1 of 6 veterinary teaching hospitals between 1984 and 1992 in which R equi infection was positively diagnosed. PROCEDURE: Results of physical examination, laboratory testing, and thoracic radiography were reviewed. Indices of racing performance were obtained for foals that recovered and eventually raced and compared with values for the US racing population. RESULTS: 83 (72%) foals survived. Foals that did not survive were more likely to have extreme tachycardia (heart rate > 100 beats/min), be in respiratory distress, and have severe radiographic abnormalities on thoracic radiographs at the time of initial examination than were foals that survived. Clinicopathologic abnormalities were not associated with whether foals did or did not survive. Forty-five of the 83 surviving foals (54%) eventually raced at least once, but none of the factors examined was associated with whether foals went on to race. Racing performance of foals that raced as adults was not significantly different from that of the US racing population. CLINICAL IMPLICATIONS: R equi infection in foals is associated with a decreased chance of racing as an adult; however, foals that eventually go on to race perform comparably to the US racing population.

Effect of diseases on the culling of Holstein dairy cows in New York State.

The effect of seven diseases on culling was measured in 7523 Holstein cows in New York State. The cows were from 14 herds and had calved between January 1, 1994 and December 31, 1994; all cows were followed until September 30, 1995. Survival analysis was performed using the Cox proportional hazards model to incorporate time-dependent covariates for diseases. Different intervals representing stages of lactation were considered for effects of the diseases. Five models were fitted to test how milk yield and conception status modified the effect of diseases on culling. Covariates in the models included parity, calving season, and time-dependent covariates measuring diseases, milk yield of the current lactation, and conception status. Data were stratified by herd. The seven diseases and lactational risks under consideration were milk fever (0.9%), retained placenta (9.5%), displaced abomasum (5.3%), ketosis (5.0%), metritis (4.2%), ovarian cysts (10.6%), and mastitis (14.5%). Older cows were at a much higher risk of being culled. Calving season had no effect on culling. Higher milk yield was protective against culling. Once a cow had conceived again, her risk of culling dropped sharply. In all models, mastitis was an important risk factor throughout lactation. Milk fever, retained placenta, displaced abomasum, ketosis, and ovarian cysts also significantly affected culling at different stages of lactation. Metritis had no effect on culling. The magnitude of the effects of the diseases decreased, but remained important, when milk yield and conception status were included as covariates. These results indicated that diseases have an important impact on the actual decision to cull and the timing of culling. Parity, milk yield, and conception status are also important factors in culling decisions.

Effects of left displaced abomasum on test day milk yields of Holstein cows.

A linear model was used to estimate the effects of left displaced abomasum on 57,383 test day milk yields collected between January 1, 1992 and December 31, 1993 in New York State from 12,572 Holstein cows in parity < or = 6. Twenty-five index categories were created to differentiate among milk collected between calving and up to 60 d after diagnosis of left displaced abomasum, milk collected > 60 d after diagnosis of left displaced abomasum, milk collected before or after diagnosis of cows with any diseases other than left displaced abomasum, and milk collected from cows that remained healthy for the entire lactation. For each parity, the statistical model included fixed effects (management, age at calving, length of dry period, previous 305-d milk yield, stage of lactation, year and season of sampling date, disease index, and DHIA SCS at milk sampling) and random effects (permanent and temporary environments) on test day milk yields. From calving to 60 d after diagnosis, cows with left displaced abomasum yielded on average 557 kg less milk than did cows without left displaced abomasum; 30% of losses occurred before diagnosis. Milk loss increased as parity and productivity increased. Cows with left displaced abomasum were nearly twice as likely to have another disease than were cows without left displaced abomasum.

Pulmonary-locomotory interactions in exercising dogs and horses.

In exercising quadrupeds, limb movement is often coupled with breathing frequency. This finding has lead some investigators to conclude that locomotory forces, associated with foot plant, abdominal visceral displacements or lumbo-sacral flexion, are the primary determinants of airflow generation. Analysis of respiratory muscle electrical activation (EMG) and contraction profiles in chronically instrumented dogs and horses, along with measurements of esophageal pressure (Pes) changes and limb movements, provide evidence that each breath during the exercise hyperpnea is determined by respiratory neuromuscular events. Specifically: (1) Phasic diaphragmatic EMG and tidal shortening are always synchronous with decreases in Pes; (2) decrements in Pes are always associated with inspiratory flow generation; and (3) strict phase coupling between breathing and stride frequency is not obligatory. Thus, although locomotory-associated forces may minimally assist with flow generation, they are not the primary determinants of breathing during exercise.

The effect of exercise on diaphragmatic activation in horses.

Horses chronically-instrumented with costal diaphragmatic electromyographic electrodes were studied during exercise while unencumbered by a breathing mask. Exercise-associated changes in esophageal (Pes), gastric (Pga) and transdiaphragmatic (Pdi) pressures were measured and related to diaphragmatic electromyographic activity (CS EMG) and to left forelimb impact. In all breaths examined, CS EMG always coincided with decrements in Pes. For all exercise trials, linear increases in CS EMG, Pga and Pdi and linear decreases in Pes, as a function of exercise intensity, always occurred. During all gaits, breathing frequency (fR) was entrained with stride frequency (fS) one for one. However, a constant phase-coupling relationship between fR and fS, observed when horses cantered and galloped, was absent when horses walked or trotted. We conclude that biomechanical forces contribute minimally to ventilation in exercising horses, that the diaphragm is always phasically active during each breath and its total electrical activity and mechanical output are proportional to the exercise hyperpnea.

The association between cumulative milk yield, days open, and days to first breeding in New York Holstein cows.

The associations among milk yield, days open, and days to first breeding were studied in 15,320 Holstein cows, calving between June 1990 and November 1993, in 26 New York herds. Survival analysis, incorporating the Cox proportional hazards model, was used to quantify the effect of milk yield and other covariables on days open and days to first breeding. Sensitivity analysis was also performed. Sixty-day cumulative individual milk yield, calving season, parity, and herd were included in all models. Several diseases and their lactational risk also were studied as potential confounders: retained placenta (5%), milk fever (1%), ketosis (3%), metritis (6%), abomasal disorder (5%), mastitis (5%), and cystic ovary (3%). Cows yielding milk in the highest quintile had a slightly lower conception rate than did cows yielding milk in the lowest quintile. Conception rate varied with parity and season. Retained placenta, metritis, and cystic ovary lowered the conception rate. High yielding cows were more likely to be inseminated than were low yielding cows. Older cows and those with metritis, mastitis, and cystic ovary had lower rates on insemination. These results indicate that conception and insemination might be influenced by factors related to management (e.g., culling) and to the cow (e.g., disease history) but that increased milk yield plays a very minor role.

The association between previous 305-day milk yield and disease in New York State dairy cows.

Logistic regression was used to examine the association between milk yield and disease. We studied 8070 cows of second or higher parity from 25 New York State Holstein herds, calving between June 1990 and November 1993. Previous 305-d mature equivalent milk yield was used because most of the disorders studied occurred too early in lactation for current milk yield to be considered. Seven disorders were studied: retained placenta, metritis, ovarian cyst, milk fever, ketosis, abomasal displacement, and mastitis. A separate model was used for each disorder. Each model included, in additional to milk yield, parity, calving season, and heard. Results showed that higher milk yield was not a risk factor for any disease except mastitis. However, the association between higher previous milk yield and mastitis does not necessarily imply causation.

Regulation of respiratory muscle activities during chemoreceptor stimulation in adult horses.

We examined the electromyographic activity of the costal portion of the diaphragm and the transverse abdominal and external oblique muscles in 6 chronically instrumented awake adult horses during eupneic breathing, during 2 levels of hypercapnia (fractional concentration of inspired CO2; FICO2 = 0.4 and 0.6), and during 2 levels of hypocapnic hypoxia (FIO2 = 0.15 and 0.12). Using the inert gas technique, we also measured the end-expiratory lung volumes of the 6 horses during eupnea, 6% CO2 challenge, and 12% O2 breathing. During eupneic breathing, phasic electrical activity of these 3 muscles was always present and was preceded by the onset of mechanical flow. At progressive levels of hypercapnia, the magnitude of inspiratory and expiratory electrical activity increased, and for the expiratory muscles, this recruitment coincided with significant (P < 0.05) increases in peak expiratory gastric pressure. However, during hypocapnic hypoxia, differential recruitment patterns of the respiratory muscles were found. The electrical activity of the diaphragm increased in magnitude and occurred sooner relative to the onset of mechanical flow. The magnitude and onset of abdominal expiratory activity failed to increase significantly during these episodes of hyperpnea and this pattern of activity coincided with decrements in peak expiratory gastric pressure. Despite alterations in muscle recruitment patterns during these hyperpneic episodes, end-expiratory lung volume remained unchanged. Thus, we conclude that adult horses respond similarly to awake dogs during peripheral and central chemoreceptor stimulation.

Production evaluation techniques based on lactation curves.

Test day data on milk yield for individual cows were generated using Monte Carlo simulation consisting of 1000 herds. Each herd contained 30 second lactation cows for each of 2 yr. Three scenarios were simulated with increasing effects of test day and seasonality. For each test day, several statistics were calculated for each cow: test day data on yield deviated from expectations, deviated test day data on yield transformed to account for correlation of consecutive test day data on yields, 305-d mature equivalent estimates, and changes in these values from the previous test day. A probability value for each herd was calculated for test of month of lactation effects using ANOVA models with and without cows in the model. No month of lactation effects were simulated. The distribution of generated probability values were tested for uniformity using a chi-square test. The distribution of probability values associated with the change in test day deviations were most nearly uniform, and results for these variables were similar when the cow effect was removed from the analysis model. The transformed variables also provided a fairly uniform set of probability values, although interpretation of these statistical tests was more difficult. Tests based on mature equivalent, 305-d records were oversensitive.

Vagal contributions to respiratory muscle activity during eupnea in the awake dog.

We examined the effects of reversible vagal cooling on respiratory muscle activities in awake chronically instrumented tracheotomized dogs. We specifically analyzed electromyographic (EMG) activity and its ventilatory correlates, end-expiratory lung volume (EELV) and diaphragmatic resting length via sonomicrometry. Elimination of phasic and tonic mechanoreceptor activity by vagal cooling doubled the EMG activity of the costal, crural, and parasternal muscles, with activation occurring sooner relative to the onset of inspiratory flow. Diaphragmatic postinspiration inspiratory activity in the intact dog coincided with a brief mechanical shortening of the diaphragm during early expiration; vagal blockade removed both the electrical activity and the mechanical shortening. Vagal blockade also doubled the EMG activity of a rib cage expiratory muscle, the triangularis sterni, but reduced that of an abdominal expiratory muscle, the transversus abdominis. Within-breath electrical activity of both muscles occurred sooner relative to the onset of expiratory flow during vagal blockade. Vagal cooling was also associated with a 12% increase in EELV and a 5% decrease in end-expiratory resting length of the diaphragm. We conclude that vagal input significantly modulates inspiratory and expiratory muscle activities, which help regulate EELV efficiently and optimize diaphragmatic length during eupneic breathing in the awake dog.

Vagal modulation of respiratory muscle activity in awake dogs during exercise and hypercapnia.

Using chronically instrumented awake tracheotomized dogs, we examined the contributions of vagal feedback to respiratory muscle activities, both electrical and mechanical, during normoxic hypercapnia (inspired CO2 fraction = 0.03, 0.04, 0.05, and 0.06) and during mild treadmill exercise (3, 4.3, and 6.4 km/h). Cooling exteriorized vagal loops eliminated both phasic and tonic mechanoreceptor input during either of these hyperpneas. At a given chemical or locomotor stimulus, vagal cooling caused a further increase in costal, crural, parasternal, and rib cage expiratory (triangularis sterni) muscles. No further change in abdominal expiratory muscle activity occurred secondary to vagal cooling during these hyperpneas. However, removal of mechanoreceptor input during hypercapnia was not associated with consistent changes in end-expiratory lung volume, as measured by the He-N2 rebreathe technique. We conclude that during these hyperpneas 1) vagal input is not essential for augmentation of expiratory muscle activity and 2) decrements in abdominal expiratory muscle activity may be offset by increments in rib cage expiratory muscle activity and contribute to the regulation of end-expiratory lung volume.

Anesthetic management of an incisional dehiscence in recovery following exploratory laparotomy in a horse.

A 5-year old Arabian mare fell during recovery from general anesthesia after an exploratory laparotomy. This fall resulted in dehiscence of the abdominal closure, and a substantial amount of intestines were exteriorized. Chemical and manual restraints were rapidly used to prevent trauma to the exposed intestines. A second general anesthesia was initiated to clean the intestines and close the incision. Multiple anesthetic problems were encountered, including arterial hypotension and hypoxemia. The horse recovered from the second general anesthesia and surgery, and all complications gradually resolved. The horse was discharged and has not had further problems to date.

Influence of sedative and anesthetic agents on intradermal skin test reactions in dogs.

To determine the effects of 9 sedative/anesthetic drug protocols on intradermal skin testing, an experimental state of type-I hypersensitivity was created. Intradermal skin tests were performed on 6 dogs, using positive and negative controls and a series of tenfold dilutions of Asc-1 allergen prior to drug administration. Approximately 4 hours later, the dogs were given 1 of the following drugs: acepromazine (low dose and high dose); ketamine hydrochloride with diazepam; thiamylal; oxymorphone; halothane; methoxyflurane; or isoflurane. The intradermal skin test then was repeated, and was scored objectively and subjectively. Objective scores were unaffected by any of the drugs. Subjective scores were affected in that acepromazine decreased wheal size and the induration of the intradermal skin test reaction sites.

Equipment for inhalation anesthesia.

Inhalation anesthesia has three requirements: delivery of oxygen, delivery of an appropriate concentration of a volatile anesthetic agent, and removal of carbon dioxide. Halothane and isoflurane are the most commonly used anesthetic agents. They are usually delivered with a semiclosed circle system using an out-of-the-circuit vaporizer. Carbon dioxide is eliminated by chemical absorption and by flow of excess oxygen and waste anesthetic agent through the pop-off valve. These gases should be scavenged to prevent room contamination. A variety of ancillary equipment is available to assist the anesthetist during the procedure.

Epizootiologic patterns of diabetes mellitus in cats: 333 cases (1980-1986).

Medical records from 333 cats with diabetes mellitus were studied retrospectively, using epidemiologic methods to determine the incidence of and risk factors for diabetes mellitus in this species. Abstracts were derived, using the Veterinary Medical Data Program with its 17 participating academic institutions in the United States and Canada. A reference population of 135,651 cats was derived from the same hospital population and time span (July 1980 to June 1986). The incidence of diabetes mellitus in cats was determined to be 2.45 cases/1,000 cat-years-of-risk during the 6-year study period. Breed had no detectable effect on risk for diabetes mellitus. In contrast, body weight, age, gender, and neutering had a significant (P less than or equal to 0.01) effect. Body weight of cats was categorized as being less than or greater than or equal to 6.8 kg. The higher body weight, probably indicating obesity, contributed a 2.2-fold increase in risk, even after adjustment for age and gender (adjusted odds ratio). The etiologic fraction for high body weight was 3.8%, suggesting that an estimated 3.8% of cases of diabetes mellitus was attributable to this factor alone. Over 50% of diabetic cats were greater than 10 years old, and the etiologic fraction for age greater than 7 years alone was 73.5%. Age was a significant (P less than 0.001) and the most important single risk factor for development of the disease in cats, with adjusted odds ratios of 8.3 and 14.4 for age 7 to 10 years and greater than 10 years, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Endomyocardial biopsy in cats.

A technique for transvenous endomyocardial biopsy of the right ventricle was developed and evaluated for safety and efficacy in anesthetized healthy cats positioned in left lateral recumbency. At least 6 endomyocardial biopsy specimens were obtained from the right ventricle or interventricular septum of 11 cats. In 4 cats, the right jugular vein was torn during attempts to pass the introducing catheter into the right ventricle; however, in only 1 cat did this preclude catheter passage. This cat's heart was biopsied via the left jugular vein. Except for damage to the jugular vein, complications were infrequent, and the biopsy procedure was well tolerated by all cats.

Modified transvenous endomyocardial biopsy technique in dogs.

A technique for transvenous endomyocardial biopsy of the right ventricle was developed and evaluated for safety and efficacy in healthy dogs and dogs with dilated cardiomyopathy positioned in lateral recumbency. This technique allowed acquisition of multiple biopsy specimens from the right ventricle of each of 22 hemodynamically normal dogs and 40 of 42 dogs with congestive heart failure. In 2 dogs with dilated cardiomyopathy, transvenous access to the right ventricle could not be achieved, but left ventricular biopsy was performed without complication. Complications were infrequent, and dogs recovered to at least their baseline status within 48 hours. Evaluation of the efficacy and complication rate of the procedure with each of the 2 biopsy instruments currently available identified no differences between them.

Cardiovascular and respiratory effects of inspired oxygen fraction in halothane-anesthetized horses.

Anesthesia of equids is associated with pulmonary dysfunction. Cardiovascular and respiratory effects of inhalation anesthetic agents and duration of anesthesia have been studied, using oxygen as the carrier gas. To our knowledge, the effects of inspired oxygen have not been determined. We studied the cardiovascular and respiratory effects of 2 inspired oxygen fractions (0.30 and greater than 0.85) in 5 laterally recumbent, halothane-anesthetized horses. Mean systemic arterial blood pressure, cardiac output, central venous pressure, pulmonary arterial pressure, arterial pH, and arterial base excess were similar in horses of the 2 groups during 4 hours of anesthesia at constant end-tidal halothane concentration. End-tidal partial pressure of CO2, arterial partial pressure of CO2 and O2, and alveolar-to-arterial O2 tension difference were greater in horses exposed to the higher oxygen concentration. On the basis of the data obtained, we suggest that greater hypoventilation and ventilation/perfusion mismatch occur when horses are breathing high-oxygen fraction. Arterial partial pressure of O2 was not different between the 2 groups of horses after they were disconnected from the anesthesia circuit and allowed to breathe room air. Horses recovered from anesthesia without complications.