Response of organically managed grassland to available phosphorus and potassium in the soil and supplementary fertilization: field trials using grass–clover leys cut for silage

Abstract. Effective use and recycling of manures together with occasional and judicious use of supplementary fertilizing materials forms the basis for management of phosphorus (P) and potassium (K) within organic farming systems. Replicated field trials were established at three sites across the UK to compare the supply of P and K to grass–clover swards cut for silage from a range of fertilizing materials, and to assess the usefulness of routine soil tests for P and K in organic farming systems. None of the fertilizing materials (farmyard manure, rock phosphate, Kali vinasse, volcanic tuff) significantly increased silage yields, nor was P offtake increased. However, farmyard manure and Kali vinasse proved effective sources of K to grass and clover in the short to medium term. Available P (measured as Olsen-P) showed no clear relationship with crop P offtake in these trials. In contrast, available K (measured by ammonium nitrate extraction) proved a useful measurement to predict K availability to crops and support K management decisions.     

Aortic valvular dysplasia in a calf.

Aortic valvular dysplasia, a congenital abnormality not previously reported in cattle, was diagnosed in a calf with a pulsating mass at the base of its neck, an enlarged area of cardiac dullness and a loud (grade IV/V) systolic cardiac murmur. Electrocardiography and thoracic radiography demonstrated that the left atrium and ventricle were enlarged. Dysplasia of two aortic valve cusps and post stenotic dilatation of the ascending aorta were identified by echocardiography and confirmed post mortem.     

Effects of detomidine on equine oesophageal function as studied by contrast radiography

The effects of sedation with detomidine on oesophageal function were assessed by contrast radiography in 10 healthy adult thoroughbred horses. Barium swallows were monitored by means of image intensification, first without sedation and then after the intravenous administration of detomidine at doses of 10 and 20 micrograms/kg bodyweight. The transit time of contrast agent to the oesophageal hiatus was recorded and each swallow was scored for markers of oesophageal dysfunction. Analysis of the data indicated that there were highly significant dose dependent increases in the transit time, the retention of barium within the longitudinal mucosal folds, and retrograde peristalsis and pooling of contrast agent within the oesophagus at both the thoracic inlet and caudal to the base of the heart. The degree of gastrooesophageal reflux was not affected at either dosage. These changes in oesophageal function were similar to those recorded from cases of grass sickness and indicate that care should be taken in the interpretation of studies of swallowing in animals that have been given detomidine before a radiographic examination.     

Kinetic study of serum gentamicin concentrations in baboons after single-dose administration

This study establishes preliminary pharmacokinetic data on the use of gentamicin sulfate administered IM to baboons. Serum concentrations greater than or equal to 12 micrograms/ml are generally agreed to cause toxicosis in human beings. On the basis of preliminary test results suggesting that the manufacturer's recommended dosage for dogs of 4.4 mg/kg of body weight caused potentially toxic serum concentrations, a dosage of 3 mg/kg was chosen to conduct a single-dose kinetic study in 6 baboons. Using a single-compartment model, the gentamicin serum half-life for IM administration of 3 mg of gentamicin/kg was 1.58 hours, and serum concentrations remained below the potentially toxic concentrations reported for human beings. We suggest that a dosage of 3 mg/kg is safer than a dosage of 4.4 mg/kg administered IM to baboons. Minimal inhibitory concentrations for 2 Pseudomonas aeruginosa isolates were less than or equal to 1 micrograms/ml. On the basis of our measured elimination half-life of 1.58 hours, it is reasonable to suppose that dosing q24 h will be inadequate to maintain therapeutic serum concentrations. We calculate that serum concentrations will remain at or above our measured minimal inhibitory concentration for P aeruginosa (1 micrograms/ml) for 100% of the treatment time if the animal is dosed q 6h, 78% for dosing q 8h, and 52% for dosing q 12h. Therefore, we suggest 3 mg/kg, q 8h or q 6h as appropriate dosing schedules for the use of gentamicin sulfate administered IM to baboons.     

MYELOID NEOPLASIA IN A DOG

A 4-year-old Scotch Collie bitch was presented for examination because of hyperthermia and anaemia. Haematological examination and bone marrow biopsy led to a diagnosis of myeloid neoplasia. At autopsy there was slight enlargement of the liver, spleen and some lymph nodes. Microscopic examination revealed extensive infiltration of these tissues by neoplastic myeloid cells.     

Systemic availability of o,p'-DDD in normal dogs, fasted and fed, and in dogs with hyperadrenocorticism

The systemic availability of o,p'-DDD was studied in 12 normal dogs and seven dogs with pituitary-dependent hyperadrenocorticism (PDH). The drug was given by mouth at 50 mg kg-1 and plasma o,p'-DDD concentrations were determined by gas-liquid chromatography. First, six normal dogs were given the drug three times at intervals of one week in a Latin square pattern. Systemic drug availability was found to be very poor from intact tablets in fasted dogs, better with pure drug dissolved in maize oil given by stomach tube, and best with ground tablets mixed in oil poured on dog food. Then six normal dogs and five with PDH were given one dose of o,p'-DDD as intact tablets in dog food. Systemic drug availability was good in the normal animals and, for unknown reasons, better in dogs with PDH. The half-time of elimination was shorter in dogs with PDH than in normal ones. There was evidence of a gradual rise in plasma o,p'-DDD concentrations in seven dogs with PDH treated with 25 mg kg-1 every 12 hours for 14 or 20 days. The interaction between food and o,p'-DDD probably contributes to the variation in clinical response of dogs treated with the drug. The efficiency of therapy with o,p'-DDD should be improved considerably by administering the drug with food.     

Comparison of inhibition of polymerisation of mammalian tubulin and helminth ovicidal activity by benzimidazole carbamates

The correlation between the inhibition of hatching of Haemonchus contortus eggs and inhibition of mammalian tubulin polymerisation by benzimidazole carbamates has been investigated. The hatching process was observed to be independent of the biomass (eggs plus debris) over a 6-fold range and the early (E1-E3) stages of egg development, but was dependent on the concentration of co-solvent (DMSO) and time of incubation. Benzimidazole carbamates with strong inhibitory activity against mammalian tubulin were potent inhibitors of egg hatch, while non-inhibitors failed to prevent hatching. It is postulated that the primary mode of action of these drugs on nematode eggs is the inhibition of microtubule-dependent processes within the developing egg. The implications and limitations of this correlation are discussed.     

Characterizing biological variability in livestock blood cholinesterase activity for biomonitoring organophosphate nerve agent exposure.

A biomonitoring protocol, using blood cholinesterase (ChE) activity in livestock as a monitor of potential organophosphate nerve agent exposure during the planned destruction of US unitary chemical warfare agent stockpiles, is described. The experimental design included analysis of blood ChE activity in individual healthy sheep, horses, and dairy and beef cattle during a 10- to 12-month period. Castrated and sexually intact males, pregnant and lactating females, and adult and immature animals were examined through at least one reproductive cycle. The same animals were used throughout the period of observation and were not exposed to ChE-inhibiting organophosphate or carbamate compounds. A framework for an effective biomonitoring protocol within a monitoring area includes establishing individual baseline blood ChE activity for a sentinel group of 6 animals on the bases of blood samples collected over a 6-month period, monthly collection of blood samples for ChE-activity determination during monitoring, and selection of adult animals as sentinels. Exposure to ChE-inhibiting compounds would be suspected when all blood ChE activity of all animals within the sentinel group are decreased greater than 20% from their own baseline value. Sentinel species selection is primarily a logistical and operational concern; however, sheep appear to be the species of choice because within-individual baseline ChE activity and among age and gender group ChE activity in sheep had the least variability, compared with data from other species. This protocol provides an effective and efficient means for detecting abnormal depressions in blood ChE activity in livestock and can serve as a valuable indicator of the extent of actual plume movement and/or deposition in the event of organophosphate nerve agent release.