Mulch effect on successive crop yields and soil carbon in Tonga

Intensification of crop production in Tonga has resulted in a move to mechanical soil preparation, often with a rotary hoe, and a consequent loss in both chemical physical fertility. An experiment was conducted on a clay loam soil (Typic Argiudoll) on the Forestry Vaini Research Station, Tongatapu Island, Tonga, to investigate the effect of a once‐off application of mulch on yield and quality of watermelon, maize and capsicum grown in rotation over a 1‐yr period. The treatments applied were a nonmulched control, transparent plastic and 200‐mm‐thick applications of locally available coconut sawdust, guinea grass and mature coconut fronds. The fresh fruit yield of watermelon in all the mulch treatments was 7.3–18.1% higher than in the nonmulched control. There was no significant effect of thick vegetative mulch on maize grain dry matter yield; however, the maize yield was significantly lower in the transparent plastic mulch than in the other treatments. The capsicum marketable fruit yield in the following crop was increased by 49–73% in all the vegetative mulch treatments compared to the non‐mulched control. The higher crop yields with the vegetative mulch were attributed to the measured lower soil temperatures and higher soil moisture in these treatments. There was no effect of mulch on soil total N (TN), but soil total C (TC), soil labile C (LC) and the carbon management index (CMI) were increased.     

Evaluation of a model for Escherichia coli O157:H7 colonization in streptomycin-treated adult cattle

OBJECTIVE: To develop a repeatable model for studying colonization with streptomycin-resistant Escherichia coli O157:H7 in adult cattle. ANIMALS: 5 adult mixed-breed beef cattle. PROCEDURES: Cattle were surgically cannulated in the duodenum, treated daily with streptomycin (33 mg/kg) via the duodenal cannula prior to and during experimental colonizations, and colonized with 10(10) CFUs of streptomycin-resistant E coli O157:H7 via the duodenal cannula. Colonization of rectal mucus and shedding in feces were monitored. Antimicrobials were administered to eliminate the colonizing strain so that 5 repeated colonization experiments could be performed. A comprehensive analysis of colonization was performed at necropsy. RESULTS: Streptomycin treatment resulted in improved experimental colonization variables, compared with untreated controls, during initiation (days 2 to 6) and early maintenance (days 7 to 12) of colonization. Elimination of the colonizing strain followed by 5 repeated colonizations in the same animals indicated the repeatability of the protocol. Positive results of bacteriologic culture of feces 7 and 12 days after colonization were obtained in 100% and 84% of samples, respectively, across all animals and trials. At necropsy, highest magnitude recovery was in terminal rectal mucus. CONCLUSIONS AND CLINICAL RELEVANCE: The model was highly repeatable and novel with respect to streptomycin treatment, use of duodenal cannulas, and repeated colonizations of the same animals. Its use in adult cattle, from which most bovine-derived food originates, is critical to the study of preharvest food safety. The findings have implications for understanding intermittency of shedding in the field and for proposed vaccine-based interventions.     

Evaluation of peripheral and central venous pressure in awake dogs and cats

OBJECTIVE: To determine whether peripheral venous pressure (PVP) was correlated with central venous pressure (CVP) when measured by use of different catheter sizes, catheterization sites, and body positions in awake dogs and cats. ANIMALS: 36 dogs and 10 cats. PROCEDURES: Dogs and cats with functional jugular and peripheral venous catheters were enrolled in the study. Peripheral venous catheters (18 to 24 gauge) were placed in a cephalic, lateral saphenous, or medial saphenous vein. Central venous catheters (5.5 to 8.5 F) were placed in the jugular vein and advanced into the cranial vena cava. Catheters were connected to pressure transducers and a blood pressure monitor capable of displaying 2 simultaneous pressure tracings. For each animal, the mean of 5 paired measurements of PVP and CVP was calculated. The relationship between PVP and CVP when measured by use of different catheter sizes, catheterization sites, and body positions was determined. RESULTS: Mean +/- SD PVP was 5.7 +/- 5.8 mm Hg higher than CVP in dogs and 6.0 +/- 6.9 mm Hg higher than CVP in cats. However, results of multiple regression analysis did not indicate a significant correlation between PVP and CVP, regardless of catheter size, catheter position, or body position. The relationship was weak in both dogs and cats. CONCLUSIONS AND CLINICAL RELEVANCE: The PVP was poorly correlated with CVP when different catheter sizes, catheterization sites, and patient positions were evaluated. Peripheral venous pressure should not be used to approximate CVP in awake dogs and cats.     

Long-term analysis of feline calicivirus prevalence and viral shedding patterns in naturally infected colonies of domestic cats

Feline calicivirus (FCV) is a highly infectious respiratory pathogen of domestic cats. The prevalence of FCV in the general cat population is high, particularly in multi-cat households, largely because many clinically recovered cats remain persistently infected carriers. In order to assess how FCV circulates in such groups and to assess the contribution that each individual animal makes to the epidemiology of the disease, we have carried out the first detailed analysis of long-term shedding patterns of FCV in individual cats within naturally infected colonies. The prevalence of FCV in each of the groups on individual sampling occasions ranged from 0% to 91%, with averages for the individual colonies ranging from 6% to 75%. Within each of the colonies, one to three distinct strains of FCV were identified. Individual cats showed a spectrum of FCV shedding patterns over the sampling period which broadly grouped into three categories: those that shed virus relatively consistently, those that shed virus intermittently, and those that appeared never to shed virus. This is the first report identifying non-shedder cats that appear resistant to FCV infection over long periods of time, despite being continually exposed to virus. Such resistance appeared to be age related, which may have been immune-mediated, although by analogy with other caliciviruses, factors such as host genetic resistance may play a role. Given that a proportion of the population appears to be resistant to infection, clearly the cohort of cats that consistently shed virus are likely to provide an important mechanism whereby infection can be maintained in small populations.     

The challenge for the next generation of feline calicivirus vaccines

Feline calicivirus (FCV) has been shown to evolve within individual cats and in the environment of colonies. This evolution and the diversity it creates has important clinical implications, not only for the disease in cats, but also for attempts to control disease by vaccination. Generally speaking, existing vaccines appear to be very effective at controlling the majority of clinical disease. However, some concerns remain including a failure to induce sterilising immunity, occasional vaccine breakdowns, and for live vaccines, occasional vaccine-induced disease. Key areas for future vaccine development include monitoring and broadening the cross-reactivity of vaccine immunity to field viruses, especially the recently evolved highly virulent strains, and attempting to reduce/eliminate field virus shedding by vaccinated cats.     

Duration of immunity (DOI)--The regulatory issues

This paper discusses the efficacy of cat and dog vaccines, with respect to duration of immunity and regulatory issues. The European Union (EU) regulatory requirements are described: briefly, efficacy claims, which include duration of immunity, have to be specific for the product and supported by controlled laboratory and field trials. As a result, the duration of immunity shown has typically been a minimum, because of the cost and welfare implications of keeping animals for long periods of time in isolation. In contrast, in the US, duration of immunity has not traditionally been required for each individual product, only for rabies vaccines and some other vaccines for which no other products are available. The consequence of this is that in the US, various scientific authorities have produced guidelines appropriate for individual diseases. Undoubtedly this will continue, although the regulatory authorities also appear to be moving towards a position where lack of information may be indicated on the product label, and studies are required to support extended duration of immunity claims. The advantages and disadvantages of laboratory challenge studies versus field trials are discussed, and the use of alternatives such as surrogate markers of protection. The approaches used for small animal vaccines are compared to those used, for example, in human medicine. The main issue for small animals is that unlike in some other species, the aim generally is to maximise protection in the individual, rather than induce protection at the population level. The drawbacks of the present EU system are summarised, and the ways in which the situation is currently being approached and improved are presented.     

Intramolecular carbon isotopic composition of monosodium glutamate: biochemical pathways and product source identification

Monosodium glutamate (MSG) obtained as trade samples from several manufacturers was studied to determine the range of its intramolecular 13C/12C composition. Although the carbon isotopic composition of the total MSG molecule did not differ among manufacturers in most instances, significant differences were observed in the isotopic composition of the alpha-carboxyl carbon, suggesting that different proprietary strains of industrial microorganisms or MSG purification methods may impart unique isotopic fingerprints upon their products. The 13C depletion of the alpha-carboxyl carbon relative to the rest of the molecule helps constrain the identity of the potential anapleurotic carboxylating enzymes responsible for its fixation.     

Changes in bone structure of Corriedale sheep with inherited rickets: A peripheral quantitative computed tomography assessment

An inherited skeletal disease with gross and microscopic features of rickets has been diagnosed in Corriedale sheep in New Zealand. The aim of this study was to quantify the changes present in tibia from sheep with inherited rickets using peripheral quantitative computed tomography. In affected sheep, scans in the proximal tibia, where metaphysis becomes diaphysis, showed significantly greater trabecular bone mineral content (BMC) and bone mineral density (BMD). The sheep with inherited rickets had significantly greater BMC and bone area in the mid-diaphysis of the proximal tibia compared to control sheep. However, BMD in the mid-diaphysis was significantly less in affected sheep than in controls, due to the greater cortical area and lower voxel density values in affected sheep. From this it was concluded that the increased strain on under-mineralised bone in sheep with inherited rickets led to increased bone mass in an attempt to improve bone strength.     

A review of the activity,fate and mode of action of sulfonylurea herbicides

The sulfonylurea herbicides are a relatively new group of compounds which control broad-leaved weeds and some grasses in cereal crops. This literature review emphasises work reported on chlorsulfuron and met-sulfuron-methyl. The activity of the herbicides, their fate in soil and in plants, and their mode of action are discussed. In addition some of the methods of assaying these compounds are described.