A computer model study of light interception by orchards in relation to mechanised harvesting and management

The introduction of mechanised harvesting often results in a redesign of the crop canopy. Computer models have been used to predict light interception, and hence potential yield, by a range of hedgerow tree forms and spacings as a guide to the design of orchard systems for mechanical harvesting. Light interception is increased by increasing tree height, thickness and leaf-area density, and by reducing the clear alleyway. Narrow hedgerows less than 2 m high will need straddle harvesting to avoid loss of light interception and yield.     

ISOTOPIC EXCHANGE OF PHOSPHATE ON SOME PHOSPHATIC COMPOUNDS

The kinetics of isotopic exchange of phosphate on hydroxyapatite, amorphous aluminium phosphate, phosphate-treated aluminium oxide and dicalcium phosphate dihydrate were studied in aqueous suspensions as a function of solid/solution ratio and amount of added isotope. The tracer exchange reaction was independent of time for the dicalcium phosphate due to a very small amount of exchangeable phosphate found in the solid and to the high solubility of the material. For the other phosphates, a power function and/or a function composed of a series of exponential terms were found suitable for representing the tracer kinetics. The theoretical background for both functions is shown to be approximately the same. Both describe tracer kinetics for a system containing more than one solid phase. The amounts of exchangeable P were found to depend strongly on the solid/solution ratio but not on the amount of radioactivity added. The dependence of the tracer kinetics on the solid/solution ratio is due to the ageing processes that give rise to the formation of surface layers having physical and chemical properties different from those of the bulk solid.     

Serological study of ovine toxoplasmosis in Colombia: epidemiological study of a field outbreak.

A serological study, using the indirect haemagglutination test, of an outbreak of toxoplasmosis in a flock of blackface sheep is described. The serological aspects of the disease are discussed with reference to this incident, and possible sources of infection are suggested.     

Virus-like particles in buffy coat cells of normal goats and goats infected with progressive pneumonia virus.

By electron microscopy, virus-like particles (VLP) were seen in neutrophils and lymphocytes from buffy coats prepared from 5 goats inoculated with progressive pneumonia virus (PPV) and 3 noninoculated goats. The VLP were 80 to 120 nm in diameter, limited by a unit membrane, and resembled PPV, visna virus, and other members of the oncornavirus family. Some VLP seemed to have electron-dense nucleoids and external spikes. In neutrophils, VLP were observed budding into vacuoles; rarely, intravacuolar clusters were seen. In lymphocytes, VLP were seen in vacuoles. Free VLP and budding of VLP from external cell surfaces were not seen. In vitro incubation of buffy coat cells with mitogens did not affect the frequency of VLP. Although the VLP are similar to PPV, the exact nature of the particles and their relationship to PPV is not clearly understood.     

Idiopathic hemorrhagic pericardial effusion with organized thrombi in a dog

A dog was examined because of cardiac tamponade secondary to pericardial effusion. Masses adjacent to the right atrial and ventricular walls were revealed by echocardiography. Pericardectomy and biopsies of the masses established the diagnosis of idiopathic hemorrhagic pericardial effusion with organized thrombi. The dog was healthy 3 months after surgery. These organized thrombi mimicked cardiac neoplasia echocardiographically, and such a possibility should be included in the list of differential diagnoses of cardiac masses.     

Approaches to relieving aeration stress in waterlogged plants

A fertile soil contains sufficient water-filled pores to replenish losses by evapotranspiration and to sustain growth. However, too many such pores can be detrimental because the exchange of gases between the soil, plant roots and the aerial environment is impaired by the water they contain (waterlogging). The consequences include an accumulation of metabolically generated gases (such as ethylene), oxygen deficiency and the production of potentially toxic substances. Knowledge of these effects, and their consequences for growth, hormone production and inorganic nutrient uptake, enhance the prospects for ameliorating flooding injury by prophylactic or restorative means. Theexamples described are (a) the use of more porousmedia for plant containers in the nutrient film technique (NFT) of glasshouse crop production; (b) fungistatic, acid neutralising and oxygen-releasing seed coatings; (c) boron and nitrogen fertilisation; (d)foliar applications of cytokinins and gibberellins; (e) the inhibition of ethylene action or stimulation of ethylene production in aquatic species.     

Cervical fibrotic stenosis in a young Rottweiler.

An 18-month-old neutered male Rottweiler was examined because of slowly progressive spastic tetraparesis and ataxia. Signalment and clinical signs were suggestive of 2 neuronal degenerative diseases presumed to be inherited in young Rottweilers: leukoencephalomyelopathy and neuroaxonal dystrophy. Myelography revealed an extradural compression at the articulation of the second and third cervical vertebrae. At surgery, focal hypertrophy of the yellow ligament was observed to compress the spinal cord ventrally at that site.     

Patterns and relationships of plasma calcium, protein and phosphorus during the egg laying cycle of the fowl and the effect of dietary calcium

In 29 domestic hens, four blood samples were collected during the period of egg formation, at time points representing different metabolic stages. Plasma concentrations of total calcium, total phosphorus, inorganic phosphorus and total protein were measured, and the effect of adding oyster shell particles to a standard laying diet was investigated. Analyses of covariance were made and correlations between the plasma characteristics were calculated. The following were significantly correlated: total and inorganic phosphorus, calcium and total phosphorus, and calcium and protein. Each of the four characteristics showed a significant decrease during egg formation. Inorganic phosphorus reached a peak 15 h after ovulation, probably related to medullary bone resorption. Plasma total phosphorus differed significantly between chickens. Addition of oyster shell to the diet did not affect the concentration or the pattern of the plasma characteristics during egg formation and did not reduce calcium mobilisation from medullary bone during shell formation.     

An investigation into the clinical pathological changes and serological response in horses experimentally infected with Babesia equi and Babesia caballi

Serologically negative horses, as determined with the indirect fluorescent antibody test (IFA), were infected with Babesia equi and 60 days later with Babesia caballi. The only clinical signs of disease observed in these animals were a febrile reaction and slight icterus. Haematological changes included a drop in haematocrit and haemoglobin concentration, as well as lowered platelet counts. The serum concentrations of albumin, iron and phosphorus were lowered. Mildly elevated serum bilirubin and fibrinogen concentrations were observed. Antibody titres were determined with the IFA and complement fixation (CF) tests. Antibodies to B. equi were first detected between Days 10-19 and 12-38 with the IFA and CF test, respectively, while the corresponding IFA periods for B. caballi were 6-8 days after infection. The parasitaemia of both B. equi and B. caballi infections never reached the 1% level.