The pathophysiology and laboratory diagnosis of congenital portosystemic shunts in dogs

Abstract Congenital portosystemic shunts generally arise as single vascular anomalies that cause the portal blood to bypass the liver and enter the systemic venous circulation directly. The liver is primarily affected, as it is deprived of perfusion by portal hepatotrophic factors such as insulin, glucagon, and amino acids. There is progressive hepatic atrophy, and as a consequence, dysfunction. Hepatic encephalopathy can result from increased levels of ammonia and gamma-aminobutyric acid within the systemic circulation. Variably toxic amines, captans and short chain fatty acids may act as false neurotransmitters. Hypoglycaemia will exacerbate the effects of these substances. Increased concentrations of ammonia and uric acid in the urine predispose to the precipitation of ammonium biurate crystals and the formation of calculi. Haematological changes include anaemia, microcytosis, hypoproteinaemia, leucocytosis, and coagulation abnormalities. Gastrointestinal effects are common. They may be displayed as anorexia, vomiting, ptyalism, pica, diarrhoea, or polyphagia. Most dogs are less than 1 year of age at initial presentation. Diagnosis from a laboratory viewpoint will involve a consideration of the history, clinical findings, haematology, serum biochemistry and urinalysis. If the findings are suggestive of a congenital portosystemic shunt, the demonstration of elevated fasting or, more consistently, post-prandial serum bile acid concentrations, and subsequent histological examination of a liver biopsy will provide a definitive diagnosis.     

A formal method of determining the dietary amino acid requirements of laying‐type pullets during their growing period

1. The amino acid requirements of laying type pullets during the growing period can be estimated by measuring the growth of different components of the body and making use of nutritional constants that define the amount of each amino acid that is required for the production of the tissues being formed.

2. In this experiment, carcase analyses of each of three breeds of pullets were conducted at weekly intervals throughout the growth of the pullets, to 18 weeks of age. Measurements were made of body weight, gut‐fill and feather weight, and chemical analyses consisted of water, protein, lipid and ash measurements of both the body and the feathers. Each age group comprised 10 birds of each breed.

3. Gompertz functions accurately estimated the growth of both body protein and feather protein, to 18 weeks of age, from which the rate of growth of these two components of the body could be estimated. The mature weight of pullets was overestimated by the Gompertz growth curve, which may indicate that a pullet ceases to increase in body protein content once sexual maturity has been reached.

4. Using allometric relationships between the chemical components of the body and of feathers, all the components of growth could be estimated from the growth of body protein and feather protein. These components were then added together to determine the growth rate of the body as a whole.

5. The daily amino acid requirements for 4 functions were calculated, namely, those for the maintenance of body protein and feather protein, and for the gain in body protein and feather protein. These requirements were then summed to determine the requirement of pullets on each day of the growing period.

6. Using the ‘effective energy’ system, the amount of energy required by these pullets was calculated for each day of the growing period, from which the desired daily food intake of the pullets could be predicted. By dividing the amino acid requirement by this daily food intake it was possible to determine the concentration of amino acids that would be needed in the diet in order to meet the requirements of a pullet.

7. The results indicate that the ratio between the requirement for lysine and for methionine and cysteine changes dramatically during the growing period, negating the concept of a fixed ratio between all the amino acids during growth.

8. The above process is the first step in determining the optimal feeding programme for a population of pullets of a given genotype. The constraining effects, of the diet being offered and of the environment in which the pullets are housed, on the food intake and growth rate of each pullet have to be estimated, and such a theory can then be expanded to include all the individuals in the population. Only by the use: of simulation models can all these constraining effects be considered simultaneously.     

Treatment of canine aural haernatorna using an indwelling drain and corticosteroids

Aural haematomas were treated using a Pen-rose tissue drain inserted through the haematoma and left in situ for two weeks. Oral prednisolone was prescribed at a dose of 2 mg/kg for two weeks then 1 mg/kg for a further two weeks. Twenty-nine haematomas were treated in 22 dogs. Twenty-six cases resolved after a single treatment. Three ears required a second treatment two to four weeks after the initial treatment and one dog had a postoperative infection of the drain tract. No ears required more than one repeated drainage. Good cosmetic results were achieved in all cases.     

Influence of Cholinergic Blockade on the Development of Epinephrine-Induced Ventricular Arrhythmias in Halothane- and Isoflurane-Anesthetized Dogs

The arrhythmogenic effects of anesthetic drugs are assessed using the arrhythmogenic dose of epinephrine (ADE) model. The purpose of this study was to determine the influence of cholinergic blockade (CB) produced by glycopyrrolate (G) on ADE in 1.5 minimum alveolar concentration (MAC) halothane (H)- and isoflurane (I)-anesthetized dogs. Eight dogs (weighing between 12.5 and 21.5 kg) were randomly assigned to four treatment groups (H, HG, I, and IG) and each treatment was replicated three times. Anesthesia was induced and maintained with H (1.31%, end-tidal [ET]) or I (1.95%, ET) in oxygen. Ventilation was controlled (carbon dioxide [PCO₂] 35 to 40 mmHg, ET). G was administered 10 minutes before ADE determination at a dose of 22 μg/kg (11 μg/kg, intravenous [IV] and 11 μg/kg, intramuscular [IM]). The ADE was determined by IV infusion of epinephrine at sequentially increasing rates of 1.0, 2.5, and 5.0 μg/kg/min; and defined as the total dose of epinephrine producing at least four ectopic ventricular contractions (EVCs) within 15 seconds during a 3-minute infusion and up to 1 minute after the end of the infusion. Total dose was calculated as the product of infusion rate and time to arrhythmia. Data were analyzed using a randomized complete block analysis of variance. When significant (P < .05) F values were found a least significant difference test was used to compare group means. Values are reported as means ± standard error. The ADE (μg/kg) for H, HG, I, and IG were 1.53 ± 0.08, 3.37 ± 0.46, 1.61 ± 0.21, and > 15.00, respectively. Heart rates (HRs) (beats/min) and systolic pressures (mmHg) at the time of arrhythmia formation for H, HG, I, and IG were (60.3 ±4.0 and 142.0 ± 7.6), (213.0 ± 13.1 and 239.2 ± 7.1), (62.9 ± 4.5 and 151.9 ± 6.3), and (226.3 ± 6.1 and 323.5 ± 3.4), respectively. The H and I ADE were not different. The HG ADE was significantly less than the IG ADE. The H and I ADE were significantly less than the HG and IG ADE. We conclude the following from the results of this study of epinephrine infusion in halothane- and isoflurane-anesthetized dogs: (1) two distinct mechanisms are responsible for the development of arrhythmias, (2) CB produced by G significantly increases ADE but is associated with higher rate pressure products (RPP) and myocardial work, and (3) ADE methodology could be improved by determining ADE with and without CB.     

Possible role of histamine in the genesis of pulmonary arterial disease in cats infected with Toxocara cati

Kittens between 12 and 20 weeks of age were orally dosed with 6000 infective ova of Toxocara cati. Animals were sacrificed at intervals between one and eight weeks after infection to study the development of pulmonary arterial lesions. After two weeks, marked leucocyte infiltration and mild thickening of the media of some of the smaller arteries was apparent histologically . Cellular inflammatory activity progressively increased up to four weeks after infection when intimal proliferation was evident in many of the arteries. After six weeks, the arterial walls were grossly thickened with pronounced intimal proliferation which after eight weeks had resulted in complete occlusion of some vessels. The progressive arterial occlusion was associated with a three- to four-fold increase in the parenchymal mast cell population and a corresponding increase in lung histamine content. The possible role of histamine in the genesis of the arteriopathy is discussed.     

Haemodynamics, blood gas and metabolic changes after anaesthesia with chloral hydrate and magnesium sulphate in camels (Camelus dromedarius)

The effects of chloral hydrate and magnesium sulphate (1:1, 10 per cent solution) were evaluated in six healthy adult camels. A dose of 1 ml kg-1 was used. These agents produced satisfactory anaesthesia with good muscle relaxation. The changes in the electroencephalogram showed that the anaesthetic effect lasted for 45 to 60 minutes. Tachycardia and hypotension were moderate and within safe limits. Electrocardiogram studies showed ST segment elevation and primary T wave changes. The acid-base status, blood gas tensions, haemoglobin concentration, blood glucose level and the plasma concentration of total protein, sodium, potassium and chloride were not altered.     

Reproductive performance in a diallel cross among lines of mice selected for litter size and body weight

Genetic factors affecting female reproductive performance in lines of mice with a known history of selection were estimated from a 5 X 5 diallel cross. Lines were selected as follows: large litter size at birth (L+); large 6-wk body weight (W+); an index for large litter size and small 6-wk body weight (L+W-); the complementary index (L-W+) and randomly (K). Partitioning of direct and correlated responses for litter size, 6-wk body weight and related traits into average direct genetic (li) and average maternal genetic (mi) effects indicated that the magnitude of differences in li exceeded those in mi. Lines having positive responses in li were W+ greater than L+ greater than L-W+ for dam body weight, L+ greater than L+W- greater than W+ for litter size and L+ greater than (W+, L+W-) for litter birth weight, whereas L-W+ responded negatively for litter size. A positive association was found between mi for litter size and dam body weight, W+ and L-W+ being high and L+ and L+W- low for both traits. Female infertility and time from male exposure to parturition had relatively small correlated responses. Line rankings in general combining ability (gi) and net line effects were similar for the respective traits. Depending upon the line and trait involved, the relative contribution of average direct genetic and line direct heterotic (hi) effects to general combining ability [gi = (1/2) li + hi] varied. Line heterosis refers to average heterosis in crosses involving that line. Direct heterosis ( hij ) for each trait differed considerably among crosses. The three crosses showing the highest hij for litter size at birth, W+ X L-W+ (1.78), L+ X W+ (1.28) and L-W+ X L+W- (1.22), possibly had loci contributing directional dominance to litter size with frequencies of parental lines deviating in opposite directions relative to mean gene frequency. The correlation between absolute difference in parental line means and hij for litter size was not significant, suggesting that the magnitudes of absolute differences in parental means were not reliable predictors of divergence in gene frequency. Crossbred performance increased linearly with midparent values for litter size at birth (b = .88 +/- .09, R2 = .92) and dam parturition body weight (b = 1.13 +/- .04, R2 = .99), the latter trait showing an increase (P less than .01) in heterosis as midparent values increased.     

Determination of the antigenic relationships within the Massachusetts (M41) type of infectious bronchitis virus using the hemagglutination-inhibition test

The antigenic relationships, antigenic spectrum, and immunogenicity of seven IBV-Massachusetts-41 isolates were investigated using the hemagglutination-inhibition (HI) test. HI titers equal to 32 are considered suspicious, titers lower than 32 are considered negative, and titers higher than 32 are considered positive immune responses to infectious bronchitis virus (IBV). Some isolates of Massachusetts-41 ( M41 ) were capable of inducing large quantities of antibodies in chickens following inoculation and demonstrated a wider antigenic spectrum than others. Variations in antigenic spectrum observed within M41 isolates in this study are in agreement with previous reports. This variation is of importance in selecting a proper vaccine strain for a successful immunization program for IBV.     

An epornitic of avian pox in a research aviary

An outbreak of avian pox in a bird research colony was reported. Although 10 species of passerine birds were housed within the facility, clinical signs and mortality were restricted to canaries and house sparrows. Post-mortem lesions initially occurred in the upper and lower respiratory tracts and were characterized by proliferative rhinitis, proliferative bronchopneumonia, and proliferative airsacculitis, and diphtheritic lesions occurring in the esophagus were characterized by proliferative granulomatous esophagitis. Cutaneous lesions occurred subsequently in some birds, and a diagnosis was made by histopathology, electron microscopy, and virus isolation. The occurrence of diphtheritic lesions in pox infections of wild birds has been rare, and a sparrow showed an unusual combination of both diphtheritic and acute systemic lesions previously undescribed.     

Pitfalls in immunofluorescence testing in dermatology. III. Pemphigus-like antibodies in the horse and direct immunofluorescence testing in equine dermatophilosis

Indirect immunofluorescence testing for pemphigus-like antibodies was performed on 79 horses: 28 horses with various nonpemphigus dermatologic diseases, 21 horses with various nondermatologic diseases, and 30 normal horses. Pemphigus-like antibodies were detected in 6 horses: 3 normal horses with titers of 1:40, 2 horses with dermatophilosis at titers of 1:10 and 1:80, and 1 horse with lymphosarcoma at a titer of 1:320. It was concluded that equine pemphigus-like antibodies are a potential source of misinterpretation and misdiagnosis in indirect immunofluorescence testing. Direct immunofluorescence testing for whole immunoglobulin, IgG, IgM, and IgA was performed on skin lesions from 2 horses with dermatophilosis. Diffuse intercellular deposition of whole immunoglobulin and IgG was found in both horses. It was concluded that equine dermatophilosis is a potential source of misinterpretation and misdiagnosis in direct immunofluorescence testing.