Ecologically and economically valuable Pacific salmon and trout (Oncorhynchus spp.) are widespread and susceptible to the ectoparasite Salmincola californiensis (Dana). The range of this freshwater copepod has expanded, and in 2015, S. californiensis was observed in Blue Mesa Reservoir, Colorado, USA, an important kokanee salmon (O. nerka, Walbaum) egg source for sustaining fisheries. Few S. californiensis were detected on kokanee salmon in 2016 (<10% prevalence; 2 adult S. californiensis maximum). By 2020, age-3 kokanee salmon had 100% S. californiensis prevalence and mean intensity exceeding 50 adult copepods. Year and kokanee salmon age/maturity (older/mature) were consistently identified as significant predictors of S. californiensis prevalence/intensity. There was evidence that S. californiensis spread rapidly, but their population growth was maximized at the initiation (the first 2–3 years) of the invasion. Gills and heads of kokanee salmon carried the highest S. californiensis loads. S. californiensis population growth appears to be slowing, but S. californiensis expansion occurred concomitant with myriad environmental/biological factors. These factors and inherent variance in S. californiensis count data may have obscured patterns that continued monitoring of parasite–host dynamics, when S. californiensis abundance is more stable, might reveal. The rapid proliferation of S. californiensis indicates that in 5 years a system can go from a light infestation to supporting hosts carrying hundreds of parasites, and concern remains about the sustainability of this kokanee salmon population. 相似文献
This study investigated the individual variation in vertebral morphology and mineral content (as % of bone dry weight) in rapid growing underyearling smolt (n = 33) twelve weeks after transfer to seawater. The smolt, which were reared in triplicate tanks, had a large individual variation in vertebral bone mineral content (Tank A: 36.2% min, 45.2% max, 39.6% mean. Tank B: 32.6% min, 46.6% max, 40.0% mean. Tank C: 38.5% min, 47.9% max, 42.4% mean), and were subdivided into two groups based on mean within each tank: high mineral content (HMC, above tank mean, n = 15) and low mineral content (LMC, below tank mean, n = 18). Vertebrae of smolt with a low mineral content were more compressed in the anterior–posterior direction (HMC vertebral length/dorso-ventral diameter ratio 0.83, LMC 0.80). This was related to a change in the growth direction of the vertebral cone. This change occurred around transfer to seawater and was characterised by an increased angle between the wall of the cone of the vertebrae and the cranial–caudal axis, and gave the vertebrae a compressed appearance. Smolt with a high mineral content were significantly longer (HMC 28.1 cm, LMC 26.5 cm) and heavier (HMC 270 g, LMC 210 g) twelve weeks after transfer to seawater. 相似文献
This review comprises both well‐known and recently described Phytophthora species and concentrates on Phytophthora–woody plant interactions. First, comprehensive data on infection strategies are presented which were the basis for three models that explain invasion and spread of Phytophthora pathogens in different woody host plants. The first model describes infection of roots, the second concentrates on invasion of the trunk, and the last one summarizes infection and invasion of host plants via leaves. On the basis of morphological, physiological, biochemical and molecular data, scenarios are suggested which explain the sequences of reactions that occur in susceptible and tolerant plants following infections of roots or of stem bark. Particular emphasis is paid to the significance of Phytophthora elicitins for such host–pathogen interactions. The overall goal is to shed light on the sequences of pathogenesis to better understand how Phytophthora pathogens harm their host plants. 相似文献
The effect of nitrogen (N) on crop growth and productivity is mediated through effects on both light interception (green crop area) and radiation use efficiency (RUE). The effects of N nutrition on these factors were studied using data on green area index (GAI), above-ground dry matter and N uptake from growth analysis measurements in winter wheat from a number of experiments in Denmark with different application rates of N. Only measurements taken prior to anthesis were used in the statistical analyses. The N uptake was found to be proportional to GAI, and to have an additional curvilinear response to dry matter implying decreasing N concentration with increasing dry matter. This supports the hypothesis that nitrogen is associated with both the green surfaces of the crop canopy and with the dry matter component. A model of GAI expansion is presented incorporating three limiting factors: an exponential increase in GAI in thermal time, a minimum leaf area ratio, and a minimum ratio of GAI to N content in above-ground dry matter. This simple function has potential to be used as a tool for targeting timing and rates of N fertilisation in relation to a desired development of GAI. Such N application strategies should also consider the nitrogen nutrition index (NNI), which was defined based on the relationship between N uptake and both GAI and dry matter. The response of RUE to NNI showed a curvilinear response with a tendency for saturation at high NNI. The design of N application strategies should therefore ensure that low NNI is avoided during the most productive periods in the growing season. 相似文献
The long-term effects of undersowing a ryegrass catch crop in cereals was analysed with the FASSET simulation model. The model was tested on a 28-year field experiment with ryegrass catch crops in spring barley. The experiment included treatments with nitrogen (N) fertiliser rates, catch crop use and timing of tillage. The modelled effects of these treatments generally agreed with observations on crop production, soil carbon, soil nitrogen and nitrate leaching. Both the observations and the simulations predicted a yield increase of 7 kg N ha−1 and an increase in nitrate leaching of 13 kg N ha−1 due to a prehistory of 24 years with continuous use of catch crops compared to a prehistory without catch crops.
A range of scenarios was constructed to evaluate the fate of the reduced nitrate leaching on crop N uptake, N leaching, gaseous emissions and change in soil organic N, and how this fate interacts with soils and climate and management. These scenarios showed that 22–30% of the reduced nitrate leaching was subsequently leached during the following decades after termination of catch crop use. Between 35 and 40% of the reduced nitrate leaching was harvested in cereals. The exact distribution depended primarily on the soil texture. The scenarios showed that effects of catch crops should be evaluated on the long-term rather than consider short-term effects only. 相似文献
Progress in establishing if therapies provide relief to cats with degenerative joint disease (DJD)‐associated pain is hampered by a lack of validated owner‐administered assessment methods.
Hypothesis
That an appropriately developed subjective owner‐completed instrument (Feline Musculoskeletal Pain Index‐FMPI) to assess DJD‐associated impairment would have responsiveness and criterion validity.
Animals
Twenty‐five client‐owned cats with DJD‐associated pain.
Methods
FMPI responsiveness (ability to detect the effect of an analgesic treatment) and validity (correlation with an objective measure) were explored through a stratified, randomized, double blinded, placebo‐controlled, crossover 10‐week clinical study. Meloxicam was administered to effect pain relief. A linear mixed model, backward stepwise regression, and Pearson correlations were used to assess responsiveness and criterion validity with the assumption that the NSAID would increase activity.
Results
Positive responses of cats to placebo (P =.0001) and meloxicam treatment (P =.0004) were detected; however, the instrument did not detect any difference between placebo and meloxicam (linear mixed model), even for the high impairment cases. Percent meloxicam target dose administered, temperament, and total baseline FMPI score were covariates that most affected FMPI scores. Controlling for significant covariates, most positive effects were seen for placebo treatment. Positive treatment effects on activity were detected, but only for the cases designated as most highly impaired.
Conclusions and Clinical Importance
Neither responsiveness nor criterion validity were detected by the inclusion criteria for cases in this study. The data suggest that further work is indicated to understand factors affecting activity in cats to optimize inclusion criteria. 相似文献
Abstract Selection was performed for high November weight on ad libitum (AL) and restricted feeding (RF) in mink in two generations. A farm fed line (FF) was maintained as a control. The estimates of heritability for November weight were large (0.62, 0.52, and 0.73 in males and 0.68, 0.51, and 0.60 in females in the FF-, AL-, and RF-line). The results indicate that selection on AL feeding increased appetite and thereby improved feed conversion ratio while selection on RF improved feed utilization. Furthermore, the results suggest that selection for August weight produces lean mink while selection for November weight produces fat mink. 相似文献
AbstractIn this work we address the short-term postprandial dynamic changes in the equine caecal microbial composition and the microbial fermentation metabolites in the caecum. Samples were collected every half hour for 8.5 hours postfeeding from two horses on two consecutive days. The caecal content of volatile fatty acids (VFAs), lactate, and ammonia (NH3N), as well as microbiota composition and pH were analyzed. Mixed Sangers sequences generated from universal polymerase chain reaction (PCR)-amplified 16S rRNA gene were used to analyze the microbiota composition. Three main phylogroups were identified and classified as Clostridium cluster XIVa, Clostridium cluster III, and lactic acid bacteria. Furthermore, we found that the composition of the caecal microbiota was closely associated with the VFA profile. Our main findings were that short-term microbial fluctuations occur in healthy hindgut fermenting horses as a response to feed intake. 相似文献
Records from 570 scanblack mink dams with 786 lactations in the period 1989–94 were used to estimate genetic parameters for body weight and weight changes during the lactation period from parturition to 6 weeks post‐partum. Direct additive effects and effects of permanent environment were estimated using restricted maximum likelihood (REML) in univariate and bivariate models. During the first 6 weeks of lactation, the dam lost around 15% (169 g) of the body weight at parturition, the main part, 10% (112 g), during the last 2 weeks. Older dams lost more weight than yearling dams, especially during the late part of the lactation period. Dams fed ad libitum had a higher body weight during the last part of the lactation period. The litter size, the sex of the kits and the litter weight influenced weight loss of the dam, especially in the late part of the lactation period. The heritability of the direct additive effect was intermediate to high for body weight (h2a ~ 0.39–0.58), but lower for weight changes (h2a~ 0.15–0.38). The permanent environmental effect was important for the total body weight (c2 ~ 0.23–0.30) and less important for weight changes (c2 ~ 0.13), but still significant. The repeatability for weight changes between parities was intermediate to high (r ~ 0.19–0.52). 相似文献
The IGF system is related to embryo quality. We aim to determine the effect of the heat stress on the mRNA expression of IGF1 and IGF2, IGFR1 and IGFR2, IGFBP2 and IGFBP4, and PAPPA in in vitro production (IVP) blastocysts from Nelore and Holstein after ovum pick up (OPU) to better understand the differences between these breeds. Oocytes from four Nelore and seven Holstein were collected in six OPU sessions. Following in vitro maturation and fertilization using six Nelore or Holstein sires, embryos were divided into control (cultured at 39°C) and heat stress (HS; exposed to 41°C for 9 h). Blastocysts were submitted to RNA extraction. The IGF1 expression was higher in blastocysts under HS in both breeds, and the expression of IGFBP2 and IGFBP4 was higher in Holstein blastocysts under HS. The high PAPPA expression and the low expression of IGFBP2 and IGFBP4 are associated with a more efficient degradation of IGFBPs, which results in greater IGF bioavailability in Nelore blastocysts and may contribute to the superior HS tolerance in Nelore, when compared to Holstein. 相似文献