The effect of weather in modifying the pattern of pasture larval contamination withOstertagia circumcincta

Groups of 3 ewes and 6 lambs were run on each of three paddocks carrying residual pasture larval contamination ofOstertagia circumcincta, pasture larval contamination following the simulated spring rise on both types of infection. On all paddocks a rise in pasture larval contamination occurred in early August. The absence of the usual peak in June on the paddocks contaminated from the spring rise was attributed to the cold weather during April and May which slowed up development of the eggs ofOstertagia circumcincta     

The influence of weather and egg contamination on the development of third-stage larvae of Cooperia oncophora on pasture.

The influence of weather and egg contamination on the dynamics of herbage contamination with infective larave of Cooperia oncophora was investigated on artificially contaminated grass plots and in a grazing experiment with 24 first-year grazing calves from May to October 1987 in Lower Saxony, Germany. On the experimental plots the larval translation was highest at the beginning of July and in the second part of September, following high mean weekly temperatures. Between July and September peak recovery of larvae from herbage occurred 4 weeks after contamination. A seasonal pattern of larval translation similar to that on the experimental plots could be demonstrated on the grazed pastures when the number of larvae per m2 of pasture had been adjusted to the previous egg output by means of a contamination index. The resulting 'relative larval density' is regarded as a good indicator for larval development on pasture. From July to September the larval population on pasture resulted mainly from the egg contamination 2-3 weeks earlier. The short persistence of the infective larvae on herbage was probably due to the frequent and heavy rainfall throughout the season, causing a passive washout of larvae into the soil. On single pastures the larval density started to increase within 1 week after the calves had first contact with these fields. The impact of the calves on the distribution of larvae is discussed.     

Distribution of nematode larvae of sheep in tropical pasture plants

The aim of this work was to study the dynamics of parasitic nematode larvae of sheep (third larval stage), in tropical forage species. The experiment was composed of two different dry matter yield for each plant species, Pensacola grass (Paspalum saurae) and Aruana grass (Panicum maximum). The animals in the experiment were 28 Suffolk lambs that were 6–8 months old. Lambs were left in a naturally contaminated pasture for 86 days. A randomized design was adopted, collection of pasture was made every 15 days, separated into upper and lower portions and made larval enumeration. Lambs were evaluated by faecal egg count (FEC) to monitoring worm infection. The number of parasite larvae in both forages was similar (p > 0.05). However, higher (p < 0.05) infestation by helminth larvae in forage with lower dry matter yield, was observed in the upper portion of both plants studied. Animals with lower forage yield, for both forages, presented superior averages (p < 0.05) of FEC compared to higher forage yield pasture. Lambs grazing on Pensacola grass, with lower dry matter yield, showed increasing FECs over time. Lambs maintained on the pasture with higher yield of dry matter (Aruana) showed decreasing FECs over time. Similar results were observed when each pasture type was analysed for larval contamination. Epidemiologic and management implications are discussed in this work.     

Gastro-intestinal nematode parasite populations in ewes and lambs and the origin and time course of infective larval availability in pastures

Changes in the numbers of infective larvae available on pasture and the development of helminth infection in spring-born lambs were studied in an environment with a mild winter and where pastures are grazed throughout the year. Prior contamination of pastures in autumn and early winter was compared with egg deposition by lambing ewes as sources of infection. Larvae derived from eggs deposited by lambing ewes did not appear on pasture until 8 weeks after the beginning of lambing but were present in increasing numbers for the last 7 weeks before weaning at 11–15 weeks of age. Lambs exposed to prior contamination became infected earlier than those exposed only to ewe contamination, but lamb egg output made no contribution to larval numbers on pasture before weaning. Lamb growth rates to weaning did not differ between groups exposed either to prior contamination alone, to ewe egg output alone or to both, but all groups carried appreciable infections at weaning. After weaning, lambs remained on the same pastures, and those exposed to ewe contamination suffered severe trichostrongylosis 5 weeks after weaning. Lambs exposed only to over-wintered contamination also developed severe trichostrongylosis 9 weeks after weaning. The results are compared with those of similar recent studies in Britain and their implications for control of infection are discussed.     

The phenology of Onitis alexis (Coleoptera: Scarabaeidae) in the Araluen Valley: Survival in a marginal environment

The introduced African dung beetle, Onitis alexis Klug, has become established in the warmer regions of Australia. The south-eastern limit of its current distribution is Moruya, NSW, and the Araluen Valley 50 km inland. At Araluen newly emerged beetles are present in dung in late spring, summer and autumn. Egg-laying starts 1-2 weeks after emergence and continues throughout the summer and autumn, as indicated by the presence of parous females in the population and of broods under experimental pads. Eggs laid in December/January produce adults in late summer and autumn, those laid from February to April produce adults in the following spring and summer. In the laboratory, mortality of larvae is high in cold (0–16°C), wet conditions and their development is delayed in warm (25°C and 27°C), dry conditions. This delay was confirmed in the field during the summer drought of 1982-83 when predicted times of emergence (based on day-degree summation in the soil) always preceded the observed emergence time of the local population, as well as preceding the emergence of beetles developing from eggs laid at known times. Follicle resorption in adult females was related directly to increasing age and to rainfall. Dung collected from hayed-off pasture did not affect fecundity, but caused larval mortality. Adults survived the winters at Araluen in some years, and immatures survived best during dry winters, being facilitated in this by a cold-induced larval diapause. Onitis alexis larvae can survive wet or dry summers, and cold dry winters (down to about 0°C) but not wet winters. This seems to be the major factor limiting the southern distribution of the species.     

Breed Difference in Water Content of Faeces From Five Breeds of Sheep

Water content of faeces from five breeds was examined (14 weekly observations — eight sheep of each breed). A higher water content was found of faeces from New Zealand Romney Marsh than from their pasture mates of breeds originating from drier areas — Somali, Merino, Karakul; but Nandi originating from a medium to wet area had a similar dry matter content of faeces as the dry area breeds mentioned above. The growth rate in New Zealand Romney Marsh is greater than in the other breeds.     

Soil seed densities and emergence patterns in pastures in the seasonally dry tropics of northeastern Australia

Germinable seed densities in the surface (0–10 cm) soil of pasture communities growing at Lansdown, near Townsville, were measured during the late dry season before the first germinating rain and again during the following wet season after germination but before the input of new seed. Seedlings emerging in the field were counted at approximately weekly intervals during this period to determine emergence patterns. Twelve communities were sampled in 1980–81 and six were re-sampled in 1981–82. During the late dry season germinable seed densities ranged from 5000 to 40 000 seeds m^-2. Seeds of the introduced legume, Stylosanthes hamata, were present in all pastures. There were many seeds of annual grasses (Digitaria ciliaris and Brachiaria miliiformis) and sedges (Cyperus and Fimbristylis spp.) but only few seeds of perennial grasses (both native and introduced). Soil seed densities were much lower during the wet season than during the preceding dry season, particularly for the grasses. Emergence commenced and approximately 70% of all seedlings emerged on the first major rainfall of the wet season. The subsequent emergence pattern varied between years. In 1980–81 there was a gradual and continuous increase in seedling numbers under the continuously moist conditions which prevailed. In 1981–82 further emergence occurred in discrete events related to rainfall and intervening dry periods. Maximum seedling densities exceeded 34 000 seedlings m^-2 including 29 000 grass seedlings (mainly annual species). The implications of these results for species survival and pasture composition are discussed.     

Differential growth identified in salamander larvae half‐sib cohorts: Survival strategy?

In this study we describe the growth of several different larval cohorts (i.e. half-siblings of the same mother born on the same day) of a rare, xeric-adapted salamander Salamandra s. infraimmaculata Martens, 1885, under constant density and food conditions from birth to metamorphosis. The larvae spend the critical first phase of their lives in water, mostly in temporary ponds. Age and weight at metamorphosis were highly affected by varying food conditions. We have identified six different growth modes that these larvae use, both fast growing and slow growing. Each larval cohort was found to use 2-4 different such growth modes regardless of their initial weight. Fast growing modes (I-III) will enable larvae to survive dry years, and metamorphose bigger. Slow growing modes (IV-VI), used by 8% of the larval population, will enable survival only in rainy years. These last growth modes effect differential temporal dispersal in wet years by delaying the emergence of postmetamorphs onto land. Distribution of growth modes in the larval population is affected by food but not by density conditions. Late-born, fast-growing larvae will have an advantage in dry years being able to metamorphose and disperse, whereas the slow-growing larvae will survive only in wet years.     

Biology of gastrointestinal nematodes of ruminants

The development and survival of free-living stages of gastro-intestinal nematodes of small ruminants are influenced by several abiotic and biotic factors. Within the abiotic factors, most important are the environmental temperature and humidity. They regulate the development of larvae from eggs dispersed on the pasture by the animals faeces. Each parasite species that infect ruminants requires a different time to development, depending on temperature and humidity. Among trichostrongylids, Ostertagia, Teladorsagia and Nematodirus show a strong adaptation to low temperatures. Nematodirus larvae are able to survive to winter inside the egg shell. Temperature and humidity influence the distribution and survival of larvae on pasture. The larval third stage can migrate from faeces to pasture vegetation and they accumulate at the basis of vegetation where stay during the day or in the soil to avoid the desiccation. The forage species affects the migration of larvae on herbage too. Many biological factors contribute to disperse the larvae on the pasture. Dung burying beetles, coprophagous beetles and earthworms can greatly reduce the larvae of some trichostrongylids on pasture. They contribute to the spread of the faecal material on the pasture and allow the larval death as a consequence of drying.     

Observations on parasitic gastroenteritis and bronchitis in grazing calves: effect of low level feed incorporation of morantel in early season.

Pott J. M., Jones R. M. and Cornwell R. I. 1979. Observations on parasitic gastroenteritis and bronchitis in grazing calves: effect of low level feed incorporation of morantel in early season. International Journal for Parasitology9: 153–157. Twenty-four castrated Friesian calves were divided into two equal groups on a body weight basis and grazed separate halves of an infected pasture. One group was given 1.5 mg/kg per day morantel tartrate in the feed over a period extending from 2 weeks before turning out in early May to early July. The other group of calves received an equivalent amount of unmedicated food as controls. Pasture larval counts showed a similar pattern and level of infection from February to July on both pastures. This consisted of a fall from moderate winter levels to very low levels in April/July. The control pasture then showed a typical sharp rise in August to high levels extending through September and falling to moderate levels in October. The pasture being grazed by treated calves showed only a small rise in larval counts in August. The total pasture contamination was reduced by 85% compared with controls during August/October. Faecal egg and larval counts showed similar differences between treated and control calves. Mild clinical signs of parasitic gastroenteritis and bronchitis were seen in controls but not in the treated group. The latter had a weight gain advantage of 20.5 kg the difference becoming marked in the last month of the trial.     

Populations of strongyloid nematode infective stages in sheep pastures: Comparison between direct pasture sampling and tracer lambs as estimators of larval abundance

Waller P.J., Dobson R.J., Donald A.D. and Thomas R.J. 1981. Populations of strongyloid nematode infective stages in sheep pastures : comparison between direct pasture sampling and tracer lambs as estimators of larval abundance. International Journal for Parasitology11: 359–367. Over a 2-year period, numbers of infective larvae in samples of pasture herbage, and numbers of worms in previously worm-free “tracer” lambs allowed 4 weeks grazing, were compared as estimators of the abundance of infective larvae on pastures.Transformation of sample estimates of infective larval numbers per 100 g herbage dry matter (DM) and of worm numbers in tracer sheep, according to the expression y = log₁₀ (x+25), was effective in stabilizing variances. Estimates of error variance for each technique did not differ significantly among the genera Haemonchus, Ostertagia or Trichostrongylus and the pooled estimate for the tracer sheep method was 4 times greater than that for pasture sampling. From these results, more tracer sheep than pasture samples would be required to achieve the same level of precision with the two techniques. Using conventional statistical methods, the effects of numbers of pasture samples or tracer sheep on the size of the difference between two means which can be detected as significant and on the width of the confidence interval about a single mean, are illustrated. These can be used as a guide in the choice of sample sizes. Error variances for Nematodirus spp. were significantly less than for the other genera by pasture sampling, and greater by the tracer sheep technique. Possible reasons for this are discussed, but it is concluded that pasture sampling is likely to be much the more precise method for estimating Nematodirus spp. infective larval availability.Changes with time in infective larval abundance, for Haemonchus, Trichostrongylus and Nematodirus spp. which were present in moderate to low numbers, followed similar trends by both techniques. However, for Ostertagia spp. larvae, which were much more abundant, peak levels were defined more sharply and occurred earlier by pasture sampling than by the tracer method. It is suggested that worm counts from tracer sheep, especially those grazing for 4 weeks rather than shorter periods, may systematically underestimate the infective larval population on pasture at high levels of abundance owing to density-dependent worm loss.     

Phenotypic plasticity of starvation resistance in the butterfly <Emphasis Type="Italic">Bicyclus anynana</Emphasis>

Starvation resistance is an important trait related to survival in many species and often involves dramatic changes in physiology and homeostasis. The tropical African butterfly Bicyclus anynana lives in two seasonal environments and has evolved phenotypic plasticity. The contrasting demands of the favourable, wet season and the harsh, dry season have shaped a remarkable life history, which makes this species particularly interesting for investigating the relationship between starvation resistance, metabolism, and its environmental modulation. This study reports on two laboratory experiments to investigate the effects of pre-adult and adult temperatures that mimic the seasonal environments, on starvation resistance and resting metabolic rate (RMR) in adult B. anynana. In addition, we investigate starvation resistance in wet and dry seasonal form genotypes; artificial selection on eyespot size has yielded lines that only produce one or the other of the seasonal forms across all rearing environments. As expected, the results show a large effect of adult temperature. More relevant, we show here that both pre-adult temperature and genetic background also influence adult starvation resistance, showing that phenotypic plasticity in this species includes starvation resistance. The dry season form genotype has a higher starvation resistance when developed at dry season temperatures, indicating a genetic modulation of starvation resistance in relation to temperature. Paradoxically, dry season pre-adult temperatures reduce starvation resistance and raise RMR. The high overall association of RMR and starvation resistance in our experiments suggests that energy expenditure and survival are linked, but that they may counteract each other in their influence on fitness in the dry season. We hypothesize that metabolism is moderating a trade-off between pre-adult (larval) survival and adult survival in the dry season.     

Field studies on flooding and survival of overwintering large heath butterfly Coenonympha tullia larvae on Fenn's and Whixall Mosses in Shropshire and Wrexham, U.K.

1. Peatland rehabilitation projects may involve large increases in water levels if Sphagnum-based vegetation is to be restored over areas where vegetation has largely been destroyed by commercial peat-cutting processes. While this can result in the creation of cotton-sedge tussocks Eriophorum vaginatum on which large heath butterfly Coenonympha tullia larvae live, the water level changes can also lead to these tussocks being subjected to long periods of winter flooding. 2. Field trials were carried out over two winters (1996–97 and 1997–98) (1) to test laboratory predictions of the survival of C. tullia larvae under wet and dry conditions, (2) to record the behavioural responses of larvae to flooding, and (3) to determine whether vertebrate predation affected larval survival significantly. 3. Field trials confirmed the results from earlier laboratory work in that they showed that the submergence of overwintering C. tullia larvae has a marked impact on their survival. During the 1996–97 winter, 35% of the larvae placed in wet areas survived compared with 63% placed in dry areas. During the 1997–98 winter, none of the C. tullia larvae placed in wet areas survived compared with 54% of the larvae placed in dry areas. Because the depth of flooding in the wet areas was much greater in the 1997–98 winter than in the 1996–97 winter, the results from this study may reflect the survival rates of wild C. tullia larvae under moderate (1996–97 data) or severe (1997–98 data) levels of flooding. 4. The behavioural data from the field also support earlier laboratory findings and suggest that C. tullia can move in order to stay above the water surface. No evidence was found that vertebrate predation was a significant factor affecting larval survival. 5. These results suggest that raised water levels threaten C. tullia populations, but that the maintenance of suitable E. vaginatum tussocks in drier areas may ensure that a proportion of the C. tullia population survives even the wettest years.     

Aerosol Survival of Pasteurella tularensis Disseminated from the Wet and Dry States

The aerosol survival in air and in nitrogen was measured for Pasteurella tularensis live vaccine strain, disseminated from the wet and dry states. The results showed that most of the loss of viability occurred in less than 2 min of aerosol age, i.e., a rapid initial decay followed by a much slower secondary decay. In nitrogen and air, minimum survival occurred at 50 to 55% relative humidity (RH) for wet dissemination and at 75% RH for dry dissemination. This shift indicated that aerosols produced by wet and dry dissemination were not equivalent and suggested that survival might not be related to bacterial water activity or content. The results showed that rehydration is the key process with regard to survival, but that lysis on rehydration is not a primary death mechanism. The effects of oxygen were complex because it could be either protective or toxic, depending upon other conditions. The protective action of oxygen was through an effect on the spent culture suspending fluid. The latter contained a toxic component, the activity of which is suppressed by oxygen; possibly the component is pumped away during freeze-drying. A toxic effect of oxygen was not found in the presence of spent culture media because the toxicity of the latter masks such an effect. With other bacterial suspending fluids, oxygen was shown to be toxic at low RH. Similar effects with regard to oxygen toxicity were also found with a laboratory strain of P. tularensis. Differences in oxygen toxicity for aerosols generated from the wet and dry states also suggest that bacterial water content and activity do not control aerosol survival.     

Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands

Soil samples from mature and secondary forests and agricultural sites in three subtropical life zones of Puerto Rico and the US Virgin Islands were collected to determine the effects of forest conversion to agriculture and succession on soil organic carbon (C) and nitrogen (N) contents. Site characteristics that may affect soil C and N (slope, elevation, aspect, and texture) were as uniform as possible. Carbon contents (to 50 cm depth or bedrock) of cultivated sites, as a percent of corresponding mature forests, were lower in the wet (44%) and moist (31%) than in the dry (86%) life zones whereas N contents were relatively high regardless of life zone (60–130% of the mature forests). Conversion of forests to pasture resulted in less soil C and N loss than conversion to crops. The time for recovery of soil C and N during succession was approximately the same in all three life zones, about 40–50 yr for C about 15–20 yr for N. However, the rate of recovery of soil C was faster in the wet and moist life zone, whereas N appeared to recover faster in the dry life zone. Evidence for loss of soil C during cultivation and gain during succession to soil depths of 50–100 cm is presented.     

Effects of egg composition and prey density on the larval growth and survival of lake whitefish (Coregonus clupeaformis Mitchill)

Eggs were collected from two stocks of lake whitefish, Coregonus clupeaformis , in Lakes Michigan and Huron to assess the effect of egg composition and prey density on larval growth and survival. Egg composition parameters including wet weight (mg egg⁻¹), dry weight (mg egg⁻¹), percent water, total caloric content (cal egg⁻¹), caloric density (cal egg⁻¹), percent lipid content, and total lipidcontent (mg egg⁻¹) were measured. Fish hatched from six parental females in each stock were fed one of four rations (0, 18, 24, 50 brine shrimp larva⁻¹ day⁻¹) after yolk sac absorption. Length at hatch, endogenous growth, exogenous growth, and survival were measured during a 42-day laboratory experiment. Length at hatch of larvae was positively related to egg caloric content ( r ²=0.780). Endogenous growth for lake whitefish larvae was positively related to percent lipid content ( r ²=0.896) and total egg lipid content ( r ²=0.876) of parental females. Exogenous growth and survival of larval lake whitefish was positively related to prey availability. Larval fish growth was accurately modelled ( r ²=0.973) as a function of prey abundance using a threshold-corrected hyperbolic equation. These results indicate that both egg composition and prey availability have the potential to influence the growth and survival dynamics of larval lake whitefish significantly.     

Damage evolution in acetabular reconstructs under physiological testing in a saline environment

Damage development in cemented acetabular reconstructs has been studied under a combined cyclic loading block representative of routine activities in a saline environment. A custom-made environmental chamber was designed and installed on the Portsmouth hip simulator to allow testing of acetabular reconstructs in a wet condition for the first time. Damage was monitored and detected by scanning at selected loading intervals using micro-focus computed tomography (μCT). The preliminary results show that, although, as in dry cases, debonding at the bone-cement interface defined the failure of the cement fixation, the combination of mechanical loading and saline environment significantly affected the damage initiation and development, with drastically reduced survival lives of the reconstructs. Debonding was found to be initiated at the bone-cement interface near the rim of the acetabular cup, or DeLee zone I, in wet condition, as opposed to initiation in DeLee zone II near the dome region in dry cases. The survival time of the reconstruct in wet condition is less than 10% of that in dry condition under a given applied hip contact force.     

Growth and competition in annual legume—perennial grass pasture in a dry monsoonal climate

The seasonal growth characteristics of a perennial (sabi grass (Urochloa mosambicensis))-annual (Townsville stylo (Stylosanthes humilis)) pasture ecosystem in the dry monsoonal region of norther Australia are described. The phases during which the botanical composition of the ecosystem may change are dry season plant survival, germination, establishment, growth and propagation. A conceptual model with general applicability for a pasture of perennial and annual species is presented and the inter-relationships between the identified phases are indicated. For the example studied, there was a large decline in the proportion of the annual legume in the establishment phase, due to competition for restricted soil moisture. This explains the trend to grass dominance observed in sabi grass-Townsville stylo swards, and is considered to apply generally in a perennial-annual pasture in a dry monsoonal environment. Two distinct environmental periods occurred during the season and were reflected in the observed growth characteristics. During the first, the growth rate of Townsville stylo was slow and plant density fluctuated sharply. The growth rate of sabi grass also fluctuated sharply due to high temperature and radiation, and variable but limiting soil moisture. In the second period temperatures were lower and soil moisture was higher. During this period growth rate of sabi grass and tiller production declined but both the plant density of sabi grass and the growth rate of Townsville stylo increased. As sabi grass has a high initial growth rate and nitrogen and phosphorus contents which are nutritionally acceptable during the transition between the dry and wet seasons, monospecific sabi grass swards are suggested for grazing during this period.     

Effects of leaf litter and precipitation on germination and seedling survival of the endangered tree Beilschmiedia miersii

Question: What effects do leaf litter and rainfall regime have on seed germination (time and probability) and seedling survival of the endangered tree species Beilschmiedia miersii (Lauraceae)? Location: The species is a native tree from the mediterranean climate region of Chile. Seeds were collected from La Campana National Park (Chile). The study was carried out under controlled conditions at the Laboratory of Ecology, University of Chile, Santiago, Chile. Methods: During April 2001,200 seeds were assigned to four experimental treatments: high precipitation, with and without litter and low precipitation, with and without litter. Each treatment had 50 individual seeds, each seed in an individual pot. For statistical purposes, we considered each seed as one replicate. High and low values of artificial rainfall corresponded to mean dry and wet years, respectively, for the period 1958–1993 in the central zone of Chile. Results: Seeds germinated earlier, and in higher proportion, in the presence of leaf litter, but only under low rainfall. Seedling survival was insensitive to both litter and precipitation. Conclusions: We conclude that the presence of litter in native populations facilitates seed germination and recruitment of B. miersii, particularly during dry years. We suggest that the reduction of leaf litter due to extraction for gardens and horticultural activities might preclude regeneration of this endangered species.