Linking the abundance of aspen with soil faunal communities and rates of belowground processes within single stands of mixed aspen–black spruce

The occurrence of aspen (Populus tremuloides Michx.) patches within stands dominated by black spruce (Picea mariana Mill. BSP) has been shown to increase litter decomposition and nutrient cycling rates by improving soil physical and chemical properties. It is well known, however, that these processes are also influenced by the structure of the soil biota, but this factor has received less attention. In this study, relationships between forest floor properties and soil invertebrates were studied along black spruce–trembling aspen gradients in three stands of the eastern boreal forest of Canada. The forest floor layer of 36 plots differing in aspen basal area was sampled and analyzed to determine physical and chemical properties, the rates of decomposition of standard substrates, net N mineralization, as well as microbial basal respiration and metabolic quotient. Soil invertebrates were also collected using funnel-extraction and pitfall trapping methods. Based on redundancy analyses, we found that forest floor properties, the abundance and composition of soil invertebrates, and the rates of belowground processes changed along the spruce–aspen gradient. The increase in aspen basal area was associated with a reduction in forest floor thickness, moisture content and microbial biomass, and with an increase in the concentration of nutrients. It was also accompanied by changes in soil faunal communities, as soil invertebrates were associated with specific soil properties. In general, macroinvertebrates (i.e., Lumbricidae, Formicidae, Carabidae, Staphylinidae and Gastropoda) were related to the nutrient-rich forest floor associated with aspen, whereas microarthropods and Enchytraeidae tended to be negatively related to aspen basal area. According to mixed linear models, decomposition rates of standard substrates and net ammonification significantly increased along the spruce–aspen gradient. Given the functional significance of macroinvertebrates in soils, these results suggest that aspen favours the elaboration of a macrofaunal community, which in turn accelerates the rate of soil processes by having either direct or indirect influence on microbial activity. Moreover, this study shows that the changes in soil processes and in the biodiversity of soil organisms related to the presence of mixed stands can operate only in the immediate surroundings of a given tree species. Therefore, coarse-scale tree species mixing in a forest stand may have a different effect on soil biodiversity and soil processes than fine-scale mixing.     

Dilemma of virulence of Streptococcus suis: Canadian isolate 89-1591 characterized as a virulent strain using a standardized experimental model in pigs

Virulence of Streptococccus suis capsular type 2 strain 89-1591 has been controversial in literature. A standardized experimental model with specific-pathogen free piglets was used for a new evaluation of this strain. Twenty-nine piglets were allotted in 4 separated groups. Group 1 consisted of negative control animals which received broth medium. Groups 2, 3, and 4 were intravenously challenged with 2 mL of S. suis, strains 1330, 89-1591, and 166', respectively. The strain 1330 is a recognized avirulent Canadian strain. The strain 166' is a reference French virulent isolate. Pigs inoculated with strain 1330 did not present clinical signs of a S. suis infection. Contamination in organs and bacterial blood circulation were rare and lesions were almost non-existent. Infection of pigs with S. suis strain 89-1591 (group 3) and 166' (group 4) caused severe clinical problems, animals infected with S. suis 166' were the most affected. Pigs presented with clinical signs such as high body temperature, lameness, nervous symptoms, and even mortality. Lesions associated with S. suis were numerous for both strains, but more evident in animals of group 4. It can be concluded that S. suis strain 89-1591 is virulent, although its virulence seems to be lower than that of the French strain. Results of an experimental infection with strain 89-1591 may depend on different factors such as the route of inoculation and the immunological status of the animals used. Using conventional animals, with an unknown status regarding previous S. suis infections, equivocal results may be obtained, and this may explain differences reported by some authors with the same strain.     

Evaluation of Natural Chemical Compounds Against Root-lesion and Root-knot Nematodes and Side-effects on the Infectivity of Arbuscular Mycorrhizal Fungi

The survival of two species of plant parasitic nematodes: the root-lesion nematode Pratylenchus brachyurus, and the root-knot nematode Meloidogyne javanica, was evaluated in saturated atmospheres of 12 natural chemical compounds. The infectivity of two isolates of arbuscular mycorrhizal fungi: Glomus mosseae and Glomus intraradices, under identical experimental conditions, was also determined. All the compounds tested exerted a highly significant control against M. javanica and among them, benzaldehyde, salicilaldehyde, borneol, p-anisaldehyde and cinnamaldehyde caused a mortality rate above 50% over P. brachyurus. The infectivity of G. intraradices was inhibited by cinnamaldehyde, salicilaldehyde, thymol, carvacrol, p-anisaldehyde, and benzaldehyde, while only cinnamaldehyde and thymol significantly inhibited mycorrhizal colonization by G. mosseae.     

Rabies oral vaccination of foxes during the summer with the VRG vaccine bait

The vaccination of foxes by distributing vaccine baits in the environment was initiated in France in 1986. Two campaigns per year were carried out: one in the spring and one in the autumn. After the spring campaigns, only 22-52% of fox cubs consumed vaccine baits compared to 75% of the adults and 70-80% of the adults or fox cubs after autumn campaigns. In order to reduce the period of time during which fox cubs do not have access to baits and are not immunised, a vaccination campaign was organised during the summer of 1992 over a contaminated area of 25,748 km2 where vaccines had never previously been given. Vaccine bait stability was assessed during the same summer in the field and their appetence tested on captive foxes. The efficacy of the campaign was evaluated by the relative decrease in rabies incidence and the rate of bait uptake by foxes compared to those from neighbouring areas vaccinated for the first time with the same vaccine during the spring or autumn. Summer vaccination significantly increased (P < 0.01) bait uptake by fox cubs (71%) compared with spring vaccination (39%), but no significant difference was observed for adult foxes. Moreover, the decrease in rabies incidence, measured during the 6-month period following the campaigns was less pronounced after summer vaccination (49% decrease) than when the first vaccination was carried out during the spring or autumn (79 and 72% decrease, respectively). Three campaigns led to an apparent elimination of rabies when the first campaign was performed in the spring or autumn, but only to a 76% decrease in rabies incidence density index when the first campaign was performed during the summer. The high thermostability of the Raboral VRG bait permits its use during the summer for an emergency campaign. For routine vaccination plans, however, the classical calendar of spring and autumn vaccination campaigns should continue to be preferred.     

Gastric ulcers in standardbred racehorses: prevalence,lesion description,and risk factors

This study was performed to estimate the prevalence of gastric ulcers in Standardbred racehorses, to describe the lesion score and location, and to identify potential risk factors. Two hundred seventy-five (275) Standardbred horses from 5 training centers and 2 racetracks in Quebec, Canada, were studied. Historical data for the 2 months before examination were recorded for each horse, and the presence of gastric ulcers was determined by gastroscopy. A previously reported scoring system that used grades 0-3 for gastric lesions was used. Overall, 121 horses (44.0%; 95% CI, 38.1-50.1%) had gastric ulcers. The prevalence of gastric ulcers was significantly higher (P < .0001) in actively racing horses (63.3%; 95% CI, 54.7-71.2%) than in horses at rest. Multivariate analysis defined that horses in racing (OR = 9.29; 95% CI, 3.55-24.3) were significantly more likely to have gastric ulcers than horses at rest and that trotters (OR = 2.23; 95% CI, 1.28-3.86) were more likely to have gastric ulcers than pacers. The number of lesion sites (P < .0001) and poor body condition (P < .0001) were significantly associated with lesion scores. Gastric ulcers are highly prevalent in Standardbred racehorses. Furthermore, actively racing horses and trotters are more likely to have gastric ulcers. Also, poor body condition in Standardbred racehorses may be an indication that gastric ulcers are present and that lesion scores are high. The cause-and-effect relationship between poor body condition and the presence of gastric ulcers is unclear.     

Field efficacy of ivermectin plus praziquantel oral paste against naturally acquired gastrointestinal nematodes and cestodes of horses in North America and Europe

The efficacy of an oral formulation of ivermectin plus praziquantel in the reduction of nematode and cestode egg counts in horses was assessed in 273 horses under field conditions at 15 sites in North America (n = 6) and Europe (n = 9). Horses were confirmed by fecal examination to have natural infections of strongyles (100%) and tapeworms (76%). Replicates of four horses were formed at each site, and in each replicate three animals received ivermectin (0.2 mg/kg body weight) plus praziquantel (1 mg/kg body weight) oral paste and one animal remained untreated or received vehicle paste. Fecal samples were collected for fecal nematode and cestode egg counting before and 7, 8, 9, 14, 15, and 16 days after treatment. Horses treated with ivermectin plus praziquantel oral paste had significantly (P <.01) lower posttreatment strongylid and cestode egg counts (reductions of 98% or more) than controls. Combined site analyses revealed that 95% or 96% of the horses positive for cestode eggs before treatment that were treated with ivermectin plus praziquantel were negative for cestode eggs at each posttreatment fecal examination. No adverse reactions attributable to ivermectin plus praziquantel oral paste treatments were observed. The results of the studies demonstrated that ivermectin plus praziquantel paste was highly effective in reducing egg shedding by gastrointestinal nematodes and cestodes, and no adverse reactions were observed in horses treated under field conditions.     

Learning performances of honeybees (Apis mellifera L) are differentially affected by imidacloprid according to the season

To establish the sublethal concentrations domain, acute and chronic oral tests were conducted on caged honeybee workers (Apis mellifera L) using imidacloprid and a metabolite, 5-OH-imidacloprid, under laboratory conditions. The latter showed a 48-h oral LD50 value (153 ng per bee) five times higher than that of imidacloprid (30 ng per bee). Chronic feeding tests indicated that the lowest observed effect concentrations (LOEC) of imidacloprid and of 5-OH-imidacloprid on mortality of winter bees were 24 and 120 microg kg(-1) respectively. Behavioural effects of imidacloprid and 5-OH-imidacloprid were studied using the olfactory conditioning of proboscis extension response at two periods of the year. Winter bees surviving chronic treatment with imidacloprid and 5-OH-imidacloprid had reduced learning performances. The LOEC of imidacloprid was lower in summer bees (12 microg kg(-1)) than in winter bees (48 microg kg(-1)), which points to a greater sensitivity of honeybees behaviour in summer bees, compared to winter bees.     

Effect of dietary fat sources on systemic and intrauterine synthesis of prostaglandins during early pregnancy in gilts

The present experiment was conducted to determine the influence of dietary fatty acids C18:2n-6 and C18:3n-3 on the modulation of intrauterine synthesis of prostaglandin E2 (PGE2) and F2alpha (PGF2alpha) during early pregnancy in pigs. Prostaglandin E2 in uterine fluid has been previously reported to be associated with embryo survival and development. Thirty-two Yorkshire-Landrace nulliparous gilts were randomly allocated to four diets containing 5% supplemental fat. The four dietary treatments were: HT, hydrogenated tallow (26.5% C16:0 and 54.8% C18:0); SO, sunflower oil (61.3% C18:2n-6); LO, linseed oil (50.4% C18:3n-3); and SO(CLA), a mixture of sunflower oil and conjugated linoleic acids to provide 20% CLA. Treatments started 2 d after the first pubertal estrus (d -21) and lasted for 36 d (slaughter), which was 15 d after the second estrus (d 0; insemination). Fatty acids and PGE2 were measured in the peripheral blood plasma on d -19, d -7, d 0, and d 14. Fatty acids in endometrial tissues and PGE2 and PGF2alpha in the uterine fluid collected on d 15 were also measured. Concentrations of fatty acids in the plasma reflected the content of fatty acids in the diet as early as d -7. From d -7, PGE2 concentrations in the plasma were higher in gilts fed SO compared with HT (P < 0.05). Plasma PGE2 concentrations were lower (P < 0.01) on d 14 in gilts fed LO compared with HT. Total PGF2alpha contents in the uterine fluid of gilts fed LO were more than 70% lower (P < 0.05) than for the HT group. A similar trend was observed for total PGE2 content and for the ratio PGF2alpha:PGE2, but the effect (LO vs HT) was less marked (P < 0.07 and P < 0.10, respectively). There was no effect of SO or SO(CLA) on total PGE2 contents in the uterine fluid. Dietary enrichment in C18:2n-6 and/or C18:3n-3 for early pregnant gilts can influence fatty acids in plasma and endometrial tissue and can modulate circulatory and intrauterine prostaglandins.