Indigofera spicata (creeping indigo) poisoning of three ponies

Three ponies continuously grazed a pasture containing an estimated 24% Indigofera spicata (wet weight basis) for 4–6 weeks in April and May 2004. They developed ataxia, paresis, depression, muscle fasciculations, dysphagia, ptyalism and halitosis. Two also developed corneal opacity. One pony recovered with supportive treatment, but the other two were euthanased and necropsied. Neuropathology was not present in either case, but both livers had periacinar and periportal lymphocytic infiltrations and hydropic degeneration of mid‐zonal hepatocytes, with mild to moderate periacinar necrosis also evident in one. The I. spicata contained 2.66 mg 3‐nitropropionic acid (3‐NPA)/g dry matter and 1.5 mg indospicine/g dry matter. Indospicine, but not 3‐NPA, was detected in serum from both of the euthanased ponies and indospicine was detected in heart, liver and muscle from the one pony in which this assay was performed. The clinical syndrome closely resembled ‘Birdsville horse disease’ caused by I. linnaei and was similar to that reported in horses poisoned by the closely related species I. hendecaphylla and to 3‐NPA poisoning of other animals, including humans. 3‐NPA is thought to cause this neurological syndrome. To our knowledge, this is the first authenticated report of I. spicata poisoning in grazing animals. We also report here the first published evidence that 3‐NPA and indospicine exist in naturalised I. spicata in Australia and of the formation of indospicine residues in tissues of animals grazing paddocks infested with I. spicata.     

Variation in species richness among the offshore islands of the southwestern Cape

Fifteen islands lying off the southwestern Cape coast between the estuary of the Olifants River and Cape Agulhas were faunistically and floristically surveyed in the last few years. The statistical relationships between species richness, island area and distance from the mainland were examined for all visible taxa taken together and for the main taxonomic subsets. Distance from the mainland which never exceeds 9 km has no apparent effect on island species richness. In the species/area regression analysis the slopes have values varying between 0,49 for spiders and 0,77 for plants and the overall slope is 0,80. These values are apparently the highest ever reported in island biogeographic studies. The results are believed to be due to the small size (1 - 222 ha) of the islands studied coupled with a very high incidence of ecological disturbance on the smaller islands.     

Eyeworms (Thelazia lacrymalis) in one- to four-year-old Thoroughbreds at necropsy in Kentucky (1984 to 1985)

From Mar 1, 1984, to Feb 28, 1985, both eyes from 189 one- to four-year-old Thoroughbreds (88 males, 90 females, and 11 geldings) in Kentucky were examined at necropsy for eyeworms. Thelazia lacrymalis was recovered from 45% of 1-year-old horses, 26% of 2-year-old horses, 45% of 3-year-old horses, and 50% of 4-year-old horses; overall, 43% of 1- to 4-year old horses were infected. Prevalence of eyeworms in horses in the present study was comparable with that in horses of similar ages examined at necropsy in Kentucky in 2 previous studies (1975 to 1976 and in 1979), except for the lower percentage of infected 2-year-old Thoroughbreds in the present study.     

Dexamethasone reduces endotoxin-induced tumor necrosis factor activity production in vitro by equine peritoneal macrophages

This study evaluated the effect of dexamethasone on endotoxin-induced production of tumor necrosis factor (TNF) activity in vitro by equine peritoneal macrophages. Peritoneal macrophages from adult horses were cultured in the presence of dexamethasone (1-100 microM) for various time periods (2 hour, 0.5 hour, 0 hour) prior to the addition of endotoxin (5 ng/ml), then the secretion of TNF activity was evaluated. Macrophage supernatant concentrations of TNF activity were estimated by a modified in vitro cytotoxicity bioassay using the murine fibrosarcoma cell line, WEHI 164 clone 13. An experiment was performed to determine whether dexamethasone interfered with the cytolytic bioassay's ability to detect TNF activity. The endotoxin-induced TNF activity production by equine peritoneal macrophages was significantly reduced by co-incubation with 100 microM dexamethasone, but not by tested concentrations of dexamethasone less than 100 microM. This concentration of dexamethasone greatly exceeds those generally attained by therapeutic use of dexamethasone in horses. Preincubation time did not affect the ability of 100 microM dexamethasone to reduce TNF production by equine macrophages. The quantitation of equine TNF activity by its cytolytic bioassay was not altered by dexamethasone.     

Technical note: effect of corticotropin-releasing hormone on adrenocorticotropic hormone and cortisol in steers

The objective of this study was to determine an appropriate exogenous dose of bovine corticotropin-releasing hormone (bCRH) to stimulate the physiological effects of the hypothalamic-pituitary-adrenal axis in steers as a method to test the sensitivity of the pituitary and adrenal gland. Twenty 14-mo-old Holstein-Friesian steers were blocked by weight (443.7+/-2.5 kg) and randomly allotted to receive either saline (control) or bCRH (0.1, 0.3, 1.0, or 1.5 microg/kg BW). Animals were housed in a slatted-floor facility (n = 5 per pen). Indwelling jugular catheters, for both the administration of bCRH and blood collection, were fitted on d -1 of the experiment. Saline and bCRH were administered i.v. at time 0. Serial blood samples were collected at -15, 0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, and 180 min relative to time 0. Following administration of 0.1 microg of bCRH/kg BW, the peak ACTH response was not significantly different from pretreatment baseline concentrations (mean concentrations as measured at -15 and 0 min before bCRH administration). Mean ACTH concentrations from 0 to 180 min following 0.1 microg of bCRH/kg BW were not significantly different (P = 0.177) from controls. Administration of 0.3, 1.0, and 1.5 microg of bCRH/kg BW increased (P < 0.05) peak ACTH above pretreatment concentrations, and mean ACTH from 0 to 180 min for these treatments were greater (P < 0.05) than for controls. Peak cortisol responses to all bCRH treatments were greater (P < 0.05) than those to pretreatment concentrations. Mean cortisol concentrations from 0 to 180 min were greater (P < 0.05) in all bCRH-treated steers than in controls, but there were no significant differences among the bCRH treatments. The ratio of mean cortisol to mean ACTH for all bCRH doses tested differed (P < 0.05) from control values, indicating reactivity of the adrenals. In conclusion, bCRH challenge may be a useful method for testing the sensitivity of the hypothalamic-pituitary-adrenal axis in steers subjected to stressful husbandry conditions, and a minimum dose of 0.3 microg of bCRH/kg BW is required to stimulate physiological effects of stressor hormones.     

Assessment of leaf cover and crop soil cover in weed harrowing research using digital images

Objective assessment of crop soil cover, defined as the percentage of leaf cover that has been buried in soil because of weed harrowing, is crucial to further progress in post‐emergence weed harrowing research. Up to now, crop soil cover has been assessed by visual scores, which are biased and context‐dependent. The aim of this study was to investigate whether digital image analysis is a feasible method to estimate crop soil cover in the early growth stages of cereals. Two main questions were examined: (i) how to capture suitable digital images under field conditions with a standard high‐resolution digital camera and (ii) how to analyse the images with an automated digital image analysis procedure. The importance of light conditions, camera angle, size of recorded area, growth stage and direction of harrowing were investigated, in order to establish a standard for image capture and an automated image analysis procedure based on the excess green colour index was developed. The study shows that the automated digital image analysis procedure provided reliable estimations of leaf cover, defined as the proportion of pixels in digital images determined to be green, which were used to estimate crop soil cover. A standard for image capture is suggested and it is recommended that digital image analysis be used to estimate crop soil cover in future research. The prospects of using digital image analysis in future weed harrowing research are discussed.