Experimental observations on prophylactic and therapeutic vaccination against foot-rot in sheep

Extract

I have taken as my subject for this address the topic, “Change”, and will deal with two aspects of change, one the challenge of change due to new knowledge and techniques and second the change we must make in our attitude to other agricultural disciplines and ancillary veterinary personnel.     

Selenium in New Zealand pastures

In grasses and clovers the highest concentrations of selenium were found in the leaves. The selenium content of different species in spring pastures on the same soil type did not vary widely although the slower growing and more deeply rooting species contained higher levels. The concentration of selenium in a pasture varied with time of the year, the lower levels being usually associated with conditions that stimulated rapid growth of the herbage, although factors other than growth rate were also involved. Lucerne appeared to be unusual in that in some areas it accumulated much higher levels of selenium than was found in other associated species. A very wide variation in levels of selenium in pastures growing on different soils has been observed (3-1500 ng/g).

Selenium-responsive unthriftiness in grazing lambs occurred where the selenium content of spring pastures was <20 ng/g. Pastures containing >30 ng/g were apparently adequate while intermediate levels were probably marginally deficient.     

A randomised,blinded, crossover study to assess the efficacy of a feed supplement in alleviating the clinical signs of headshaking in 32 horses

Reasons for performing study: Feed supplements are commonly used by owners to alleviate headshaking; however, randomised, controlled trials are required to assess their efficacy. Objective: To determine the efficacy of a feed supplement for alleviation of the clinical signs of headshaking using a randomised, blinded, placebo‐controlled trial. Methods: Using a crossover design, 44 horses previously diagnosed with chronic idiopathic headshaking received both the supplement and a matching placebo per os for 28 days with a washout period between of 14 days. Video recordings were taken at rest and exercise prior to the study and at the end of both periods of treatment. The degree of headshaking was assessed in a blinded, randomised manner by 2 veterinary surgeons. At the same time points, owners completed a questionnaire to assess the severity of headshaking signs. A Wilcoxon signed rank test was used to compare the scores while on supplement and placebo. Results: Using the video assessments, there was no significant difference between scores while on supplement compared with placebo (P = 0.7). Using the questionnaire responses, there was no significant difference between scores for any activity when the placebo and the supplement were compared with each other. However, owners reported significant improvement during all activities for both placebo and supplement compared with pretreatment scores. Conclusions and potential relevance: The supplement offered no benefit over a placebo in alleviating the clinical signs of headshaking. There appeared to be a significant proxy placebo effect when the outcome was based on subjective owner perception of clinical signs. This study demonstrated no beneficial effect of this supplement on the clinical signs of headshaking. The study did show a significant placebo effect, thereby highlighting the necessity of properly conducted, randomised controlled trials, with blinding, to assess true treatment effects in trials in animals.     

Mange in pigs: A survey

Extract

Mange in pigs caused by Sarcoptes scabiei var. suis is reported to be common in New Zealand, but, to the writer's knowledge, no investigation has been made of the number of infested farms in any area.     

Reduced Myxobolus cerebralis Actinospore Production in a Colorado Reservoir May Be Linked to Changes in Tubifex tubifex Population Structure

Abstract

Elucidating the dynamics of a parasitic infection requiring two hosts in a natural ecosystem can be a daunting task. Myxobolus cerebralis (Mc), the myxozoan parasite that causes whirling disease in some salmonids, was detected in the Colorado River upstream of Windy Gap Reservoir (WGR) in 1988. Subsequently, whirling disease was implicated in the decline of wild Rainbow Trout Oncorhynchus mykiss in the river when WGR was identified as a point source of Mc triactinomyxons (TAMs). Between 1997 and 2004, numerous investigations began to elucidate the etiology of Mc in WGR. During this period, Mc TAM production in WGR declined more than 90%. Explanations for the decline have included differences in stream discharge between years, changes in the thermal regime of the lake, severe drought, changes in the fish population structure in WGR, and reductions in the prevalence and severity of Mc infection in salmonids in the Colorado and Fraser rivers upstream of WGR. All of these have been discredited as explanations for the reduced TAM production. In 2005, a new study was conducted to replicate the studies completed in 1998. In this paper, the results of a new real-time polymerase chain reaction assay utilized to quantify the mitochondrial 16S rDNA specific to each of four lineages of Tubifex tubifex in pooled samples of 50 oligochaetes are presented. These results suggest that compared with 1998, the densities of aquatic oligochaetes and T. tubifex have increased, TAM production has been greatly reduced, and the decline is congruent with the dominance of lineages I, V, and VI of T. tubifex—three lineages that are refractory or highly resistant to Mc infection—in the oligochaete population. While it is possible that the resistant lineages function as biofilters that deactivate Mc myxospores, the reason for the decline in TAM production in WGR remains an enigma.

Received February 15, 2012; accepted March 17, 2013     

Comparisons of the genomic RNA of Arkansas DPI embryonic passages 10 and 100, Australian T, and Massachusetts 41 strains of infectious bronchitis virus

The genomic ribonucleic acid (RNA) of Arkansas DPI at embryonic passages 10 and 100, Australian T, and Massachusetts 41 strains of infectious bronchitis virus (IBV) were compared using two-dimensional, 32PpCp-labeled oligonucleotide fingerprinting. The Arkansas DPI strain embryonic passage 10 was pathogenic for chickens and had one oligonucleotide not present in the attenuated passage 100. The remaining Arkansas DPI oligonucleotides had identical electrophoretic mobility. The fingerprint patterns of the Australian T, Massachusetts 41, and Arkansas DPI IBV genomes were dissimilar, thus indicating they were genetically distinct. The distinctive fingerprint patterns of these virus strains, all identified as IBV by other criteria, indicate considerable genomic variation. Fingerprinting is reliable and sensitive, and should be used in combination with other characterization methods for identifying and differentiating IBV strains.     

The detection and isolation of a paralysis toxin present in Argas (Persicargas) walkerae

One-day-old leghorn chickens were used in a laboratory assay to determine the toxicity of crude extracts of the tick Argas (Persicargas) walkerae and of fractions obtained during the isolation procedure. Extracts of unfed and engorged larvae, nymphae and females were tested using this in vivo test system. Only extracts of replete A. (P.) walkerae larvae produced paralysis. A toxic fraction was isolated from replete larval extracts by gel-permeation and ion-exchange chromatography. This fraction with a pI of 4,5, showed 2 major bands corresponding to a Mr of 32 kDa and 60 kDa after SDS-polyacrylamide gel electrophoresis.     

The use of biotin-labeled cDNA probes for the detection of infectious bursal disease viruses

A cDNA library was prepared from the double-stranded RNA genome of the infectious bursal disease virus (IBDV) strain ST-C. The cDNA molecules were annealed into the plasmid pUC9 and used to transform Escherichia coli strain JM107. A cDNA clone that contained IBDV-specific nucleotide sequences was selected and designated STC-1. Radiolabeled probes were prepared from STC-1 and hybridized to genome segment A of ST-C in a northern blot hybridization assay. The STC-1 cDNA was 448 base pairs in length, and its nucleotide sequence indicated that it is located near the VP-2/VP-4 junction in IBDV genome segment A. Biotin-labeled probes were prepared from STC-1 and used in a dot-blot hybridization assay to detect IBDV. Under relatively low stringency conditions of hybridization, the biotinylated probes detected four subtypes of IBDV serotype 1 and a serotype 2 IBDV isolate.     

Surgical treatment of a mural teat abscess in a cow

A 6-year-old multiparous Holstein cow was admitted for evaluation of progressive milk flow obstruction of one quarter of the udder. Physical examination findings suggested the presence of a mural teat abscess. Ultrasonography substantiated the physical examination findings and delineated the extent of the lesion. Surgical excision of the abscess en bloc yielded satisfactory functional and cosmetic results.