In this issue – December 2010

Aged horses in Queensland · Pressor therapy in neonatal foals · Fluoroscopic stents for feline urethral obstruction · Intradermal sodium lauryl sulfate as an alternative to mulesing in lambs · Monepantel faecal residues and dung fauna · Surgical spaying in yearling Brahman heifers · Anthelmintic resistance in cattle nematodes     

Introduced northern pike predation on salmonids in southcentral Alaska

Northern pike (Esox lucius) are opportunistic predators that can switch to alternative prey species after preferred prey have declined. This trophic adaptability allows invasive pike to have negative effects on aquatic food webs. In Southcentral Alaska, invasive pike are a substantial concern because they have spread to important spawning and rearing habitat for salmonids and are hypothesised to be responsible for recent salmonid declines. We described the relative importance of salmonids and other prey species to pike diets in the Deshka River and Alexander Creek in Southcentral Alaska. Salmonids were once abundant in both rivers, but they are now rare in Alexander Creek. In the Deshka River, we found that juvenile Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) dominated pike diets and that small pike consumed more of these salmonids than large pike. In Alexander Creek, pike diets reflected the distribution of spawning salmonids, which decrease with distance upstream. Although salmonids dominated pike diets in the lowest reach of the stream, Arctic lamprey (Lampetra camtschatica) and slimy sculpin (Cottus cognatus) dominated pike diets in the middle and upper reaches. In both rivers, pike density did not influence diet and pike consumed smaller prey items than predicted by their gape‐width. Our data suggest that (1) juvenile salmonids are a dominant prey item for pike, (2) small pike are the primary consumers of juvenile salmonids and (3) pike consume other native fish species when juvenile salmonids are less abundant. Implications of this trophic adaptability are that invasive pike can continue to increase while driving multiple species to low abundance.     

In this issue – March 2011

Wound healing after breech flystrike control methods in lambs · Resistance to synthetic pyrethroids in buffalo flies · Auditory function in older horses · Cutaneous asthenia in a foal · Avian trichomoniasis in an Australian avian practice · Infectious laryngotracheitis in poultry in Australia · Hepatotoxicosis in dogs eating contaminated camel meat · Pulmonary aspergillosis in a cat     

Cabora Bassa Fish Populations Before and During the First Filling Phase

Pre-impoundment surveys were made in 1973-4. The regulatory effect of continual water discharge from Kariba resulted in extensive dry-season aquatic, rooted, vegetal growth and a comparatively high small-fish population. Of a maximum of 38 species found one, Sarotherodon andersoni, was a new Middle Zambezi record. Lotic and shallow-water species were abundant; gill-nets showed moderately high catches per unit effort. In early November 1974 two-month-old Hydrocymis vittatus juveniles were present indicating an abnormal spawning time. Post-impoundment data from closure on 5 December 1974, to mid-August 1975 are given. The dam filled extremely rapidly to within 10 m of retention level but was thereafter drawn down by heavy floodgate discharge, resulting in continuous slow water-flow and the absence of any stratification or explosive plankton reproduction. Small lotic species, previously abundant, immediately disappeared or became scarce. There was a very high survival of new-spawned young of many migratory species. Growth rates, and abnormal feeding habits caused by post-impoundment stresses, of some of these are described. There was relatively poor reproduction of cichlid species. Soon after closure the first year-class predominated over all other age-groups; these juveniles, and small adult species, concentrated under mats of Elchhomia crassipes. One further species new to the area, Haplochromis carlottae, is recorded.     

Immunohistochemical identification of B and T lymphocytes in formalin-fixed, paraffin-embedded feline lymphosarcomas: relation to feline leukemia virus status, tumor site, and patient age.

The lymphocyte phenotype of 70 formalin-fixed, paraffin-embedded feline lymphosarcomas (LSAs) was determined immunohistochemically using a T cell polyclonal antibody, and a B cell monoclonal antibody. Forty-seven of 70 (67%) tumors were T cell, 19/70 (27%) were B cell, and 4/70 (6%) did not stain with either marker. Thirty-eight of 70 (54%) tumors were positive for feline leukemia virus (FeLV) antigen by immunohistochemistry (IHC), and 52/70 (74%) tumors were positive for FeLV DNA using the polymerase chain reaction (PCR). B cell tumors were as frequently FeLV-positive as T cell tumors using either IHC or PCR. Intestinal tumors were more likely to be B cell than T. The incidence of B and T cell tumors was not different among young (< or = 3 y), middle-aged (> 3 y to < or = 8 y), and old (> 8 y) cats. Both B and T cell tumors from old cats were FeLV-positive more often by PCR than by IHC. Feline leukemia virus DNA but not antigen, was detected in B cell tumors and intestinal tumors from cats > 8 y as often as it was detected in B cell tumors and intestinal tumors from cats < or = 8 y. Previously, most B cell and intestinal tumors from old cats were considered to be negative for FeLV. Here, the results suggest involvement of latent or replication-defective forms of the virus in such tumors from old cats. This study supports a role for FeLV in feline B cell as well as T cell tumorigenesis.     

Feasibility of interspecies extrapolation in determining the bioequivalence of animal products intended for intramuscular administration

To examine the validity of extrapolating parenteral product bioequivalence determinations across target animal species, the relative bioavailability of two injectable formulations of ampicillin trihydrate (PolyflexR, a water-based suspension, and Ampi-kel 10R, an oil-based suspension) was examined in calves, sheep and swine. Employing products recognized to be bioinequivalent provided an opportunity to explore potential species-by-formulation interactions. As compared with PolyflexR, Ampi-kel 10R exhibited lower area under the curve (AUC) estimates but higher peak concentrations in all target animal species. Nevertheless, marked interspecies differences were noted in the width and bounds of the confidence intervals about the differences in treatment means. Potential physiological and physico-chemical reasons for these findings are discussed.     

THE CONSERVATION OF HEAVILY–WILTED BALED HERBAGE IN SEALED POLYTHENE CONTAINERS

A conservation experiment is described in which the losses in ensiling heavily–wilted, baled herbage of 49–58% dry–matter content in a completely sealed polythene film is described. In addition, a comparison is made between silages with and without sodium metabisulphite added as a preservative. The mean DM loss for the control silages was 11.1%, and that for the metabisulphite–treated silages 12.8 %. These losses, and the individual crude–nutrient and digestible–nutrient losses are compared with those obtained for heavily–wilted and conventional silage made in lined trench silos. Metabolizable energy values for the grass and silages are also presented.     

Sediment and phosphorus delivery from field to river via land drains in England and Wales. A risk assessment using field and national databases

Abstract. As measures to reduce point source inputs of phosphorus (P) to water have been introduced, the effect of diffuse P has become more evident. Land drains can act as an effective conduit for transfer of sediment and sediment P from agricultural land to surface waters. This article describes the development of a national risk map, identifying areas of agricultural land in England and Wales that are most likely to be prone to such losses. The map is based on data obtained from a variety of sources, including field studies, laboratory-based rainfall simulation experiments and secondary sources. From these studies, eight factors relating to soil HOST class, rainfall, soil moisture deficit, land use and the type and condition of land drains were identified as influential in the process of sediment and sediment P transfer. Each factor was weighted to provide an estimate of risk and the combined total was used to plot a national risk estimate at a resolution of 25 km². The exercise suggests that large areas of England and Wales may be at risk of subsurface sediment and sediment P transfer from agricultural land to rivers. The scale of the map is insufficient for planning at the farm level, but further work incorporating similar data and principles could make it more applicable to potential end-users on the ground.