Mineralization of nitrogen in fertilizer-acidified lime-amended soils

Summary The application of NH _inf4 ^su+ -based fertilizers to soils slowly lowers soil pH, which in turn decreases nitrification rates. Under these conditions nitrification and N mineralization may be reduced. We therefore investigated the impact of liming fertilizer-acidified soils on nitrification and N mineralization. Soil samples were collected in the spring of 1987 from a field experiment, initiated in 1980, investigating N, tillage, and residue management under continuous corn (Zea mays L.). The pH values (CaCl₂) in the surface soil originally ranged from 6.0 to 6.5. After 6 years the N fertilizer and tillage treatments had reduced the soil pH to values that ranged between 3.7 and 6.2. Incubation treatments included two liming rates (unlimed or SMP-determined lime requirement), two ¹⁵N-labeled fertilizer rates (0 or 20 g N m^-2), and three replicates. Field-moist soil was mixed with lime and packed by original depth into columns. Labeled-¹⁵N ammonium sulfate in solution was surface-applied and columns were leached with 1.5 pore volumes of deionized water every 7 days over a 70-day period. Nitrification occurred in all pH treatments, suggesting that a ferilizer-acidified soil must contain a low-pH tolerant nitrifier population. Liming increased soil pH values (CaCl₂) from 3.7 to 6.2, and increased by 10% (1.5 g N m^-2) the amount of soil-derived NO₃ ^--N that moved through the columns. This increase was the result of enhanced movement of soil-derived NO₃ ^--N through the columns during the first 14 days of incubation. After the initial 14-day period, the limed and unlimed treatments had similar amounts of soil N leaching through the soil columns. Lime increased the nitrification rates and stimulated the early movement of fertilizer-derived NO₃ ^--N through the soil.     

Field comparison of the interferon-gamma assay and the intradermal tuberculin test for the diagnosis of bovine tuberculosis

An extensive field comparison of the gamma interferon (IFN-gamma) assay and the single intradermal tuberculin test for the diagnosis of bovine tuberculosis was conducted in Australia. The specificity of the IFN-gamma assay was determined by testing more than 6000 cattle from tuberculosis-free herds and varied from 96.2% to 98.1%, depending on the cut-off point chosen to define a positive reactor. For the sensitivity trial, cattle from herds being de-populated because of bovine tuberculosis were examined with both assays. The sensitivity of the IFN-gamma assay was shown to be significantly higher than the single intradermal tuberculin test and varied from 76.8% to 93.6% depending on the method of interpretation. A maximum overall sensitivity of 95.2% was obtained by testing with the IFN-gamma and the tuberculin test in parallel. The superior sensitivity of the IFN-gamma assay and the ability to adjust the sensitivity of the system depending on the task involved, will provide the Australian Tuberculosis Eradication Campaign with a valuable additional test to enable it to accomplish its goals.     

Evaluation of d,l-ethionine as a mechanism for pancreatic islet regeneration in dogs

Objective To determine whether induction of pancreatic necrosis and islet proliferation by d,l‐ethionine has potential for treating dogs with b ‐cell insufficiency. Design Eighteen mixed breed dogs of both sexes were given d,l‐ethionine at 100 mg/kg three times weekly for 2 weeks; 6 dogs were euthanased at 2, 14 and 28 d after the last dose. Methods Clinical signs during administration and recovery were assessed. Routine biochemical analyses were performed before each ethionine dose and then once weekly. Faecal samples were examined weekly for malassimilated nutrients and blood. Blood coagulation screening tests (OSPT and APTT) were determined on four dogs after ethionine administration. Intravenous glucose tolerance tests were conducted before the first and after the last ethionine dose and then fortnightly. All dogs were necropsied and pancreas, liver, kidney and jejunum were examined microscopically. Results During ethionine administration all animals displayed vomiting, inappetence, diarrhoea (often with blood), weight loss and depression. Three dogs were euthanased prematurely due to severe illness, but those allowed to recover were eating and brighter 7 d after cessation of ethio‐nine administration. Serum concentrations of TLI, amylase and lipase increased initially, then decreased, during administration but returned to normal during recovery. Concentrations of ALT, ALP, unconjugated and conjugated bilirubin increased during administration then decreased slowly. Histological examination revealed hepatic lipidosis and necrosis, but no renal or jejunal lesions. In most dogs, faecal examination demonstrated increased undigested starch and muscle, as well as increased digested and undigested fat, during ethio‐nine administration or early during the recovery period, suggesting transient malassimilation. APTT was unchanged but OSPT was prolonged in all dogs. There was no impairment of insulin secretion or glucose intolerance and C‐peptide concentrations were unaffected. Immediately after ethionine administration there was delayed insulin degradation and by day 43 there was evidence of increased insulin sensitivity. Conclusion d,l‐ethionine administration in dogs appeared not to interfere with insulin secretion, but caused clinical signs and laboratory changes indicative of pancreatic exocrine necrosis, severe hepatobiliary disease and transient malas‐similation. Pancreatic and hepatic dysfunction was severe but clinical recovery occurred after ethionine administration ceased. The severe side‐effects observed with d,l‐ethionine should preclude its potential use for treating diabetes mellitus in dogs.     

The use of tiletamine hydrochloride and zolazepam hydrochloride for sedation of the mountain brushtail possun Trichosurus caninus Ogilby (Phalangeridae: Marsupialia)

SUMMARY A combination of tiletamine hydrochloride and zolazepam hydrochloride in a 1:1 ratio by weight was used successfully to sedate mountain brushtail possums, Trichosurus caninus, in the field. A standard total dose of 50 to 60 mg provided adequate sedation for the completion of a range of handling procedures. We describe the induction time, dose rate and side-effects associated with the use of tiletamine and zolazepam in T caninus.     

Preferences of veterinarians for drugs to treat heart disease in dogs and cats

SUMMARY Responses (473) were collated from a questionnaire sent to 5054 veterinarians in Australia enquiring about drug preferences for treating cardiac disease in dogs and cats. When treating a small breed dog with endocardiosis and mild left congestive heart failure, 74% of 472 respondents used a diuretic, 67% a theophylline derivative, 27% a vasodilator and 20% a positive inotrope. Frusemide was the preferred diuretic and digoxin the preferred inotrope, but vasodilator use varied. Low sodium diets were “often recommended” by 71% of respondents. Propranolol was preferred to diltiazem for treating feline hypertrophic cardiomyopathy. Digoxin was clearly preferred for treating supraventricular dysrhythmias, while lignocaine and digoxin were preferred equally for ventricular dysrhythmias. Respondents appeared more willing than US veterinarians to use theophylline derivatives and prasozin, and less inclined to employ nitrates, hydralazine, inotropes other than digoxin, and low sodium diets.     

Sequential exhaustive extraction of a Mollisol soil, and characterizations of humic components, including humin, by solid and solution state NMR

A comprehensive sequential extraction procedure was applied to isolate soil organic components using aqueous solvents at different pH values, base plus urea (base‐urea), and finally dimethylsulfoxide (DMSO) plus concentrated H₂SO₄ (DMSO‐acid) for the humin‐enriched clay separates. The extracts from base‐urea and DMSO‐acid would be regarded as ‘humin’ in the classical definitions. The fractions isolated from aqueous base, base‐urea and DMSO‐acid were characterized by solid and solution state NMR spectroscopy. The base‐urea solvent system isolated ca. 10% (by mass) additional humic substances. The combined base‐urea and DMSO‐acid solvents isolated ca. 93% of total organic carbon from the humin‐enriched fine clay fraction (<2 μm). Characterization of the humic fractions by solid‐state NMR spectroscopy showed that oxidized char materials were concentrated in humic acids isolated at pH 7, and in the base‐urea extract. Lignin‐derived materials were in considerable abundance in the humic acids isolated at pH 12.6. Only very small amounts of char‐derived structures were contained in the fulvic acids and fulvic acids‐like material isolated from the base‐urea solvent. After extraction with base‐urea, the 0.5 m NaOH extract from the humin‐enriched clay was predominantly composed of aliphatic hydrocarbon groups, and with lesser amounts of aromatic carbon (probably including some char material), and carbohydrates and peptides. From the combination of solid and solution‐state NMR spectroscopy, it is clear that the major components of humin materials, from the DMSO‐acid solvent, after the exhaustive extraction sequence, were composed of microbial and plant derived components, mainly long‐chain aliphatic species (including fatty acids/ester, waxes, lipids and cuticular material), carbohydrate, peptides/proteins, lignin derivatives, lipoprotein and peptidoglycan (major structural components in bacteria cell walls). Black carbon or char materials were enriched in humic acids isolated at pH 7 and humic acids‐like material isolated in the base‐urea medium, indicating that urea can liberate char‐derived material hydrogen bonded or trapped within the humin matrix.