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LC LLOYD 《Australian veterinary journal》2002,80(3):168-169

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Protection against enzootic pneumonia of pigs: intraperitoneal inoculation with live LKR strain of Mycoplasma hyopneumoniae     

LC. LLOYD  GS. COTTEW  DA. ANDERSON † 《Australian veterinary journal》1989,66(1):9-12

Pigs obtained from a mycoplasma-free piggery were randomised into 4 groups of 9. Groups 1 and 2 were injected by the intraperitoneal route with liquid culture of the LKR strain of Mycoplasma hyopneumoniae. Group 1 was injected once and group 2 twice. Group 3 was made up of pigs inoculated by the intranasal route with the virulent Beaufort strain of M. hyopneumoniae; they served as the source of infection for the challenge. Group 4 were uninfected, uninjected controls. Six weeks after the last injection, groups from 1 to 4 were placed in contact. Seven of the pigs in the 1-dose group and 6 in the 2-dose group were free of lesions at necropsy 6 weeks after challenge. Of the two pigs with lesions in the 1-dose group one had only a small lesion but the other had extensive lesions; it had not shown an antibody response after injection of culture. The lesions in the 3 pigs in the 2-dose group were all small. All 9 control pigs had lesions which varied from medium to large in size. The difference in the incidence of pneumonia between the injected and control groups was significant (P less than 0.05) and the proportion of severely affected pigs in the vaccinated groups was significantly lower (P greater than 0.01). There was no difference between those given one dose of vaccine and those receiving 2 doses.  相似文献   

Existence Value,Contingent Valuation,and Natural Resources Damages Assessment     

GLENN C. BLOMQUIST  JOHN C. WHITEHEAD 《Growth and change》1995,26(4):573-589

ABSTRACT The purpose of this paper is to review recent developments in economics and public policy with regard to environmental resources. We describe the traditional concepts of externalities, public goods, efficient property rights, and the more recent concept of existence values for wilderness areas and other natural resources. A feature is the inclusiveness of modem economic theory. We trace the development of economic approaches to estimating values. We briefly review approaches based on observable market behavior and contingent market responses. Contingent valuation plays a vital role in estimation because it is the sole technique available for estimating the potentially important existence values. Benefit-cost analysis for regulatory decisions and natural resource damages assessment for implementation of Superfund legislation are discussed. We conclude that estimates of existence values based on contingent valuation can be useful especially when the alternative is greater reliance upon an imperfect political process.  相似文献   

Soil carbon availability affects nitrogen transformation under irrigated lucerne     

Adriano S. NASCENTE  Jonathan NU?EZ  Scott L. GRAHAM  Gabriel Y. K. MOINET  John E. HUNT  Graeme N. D. ROGERS  David WHITEHEAD 《土壤圈》2021,31(6):977-980

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A Physoderma disease of barnyard grass     

THIRUMALACHAR MJ  WHITEHEAD MD 《Science (New York, N.Y.)》1953,118(3075):693-694

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Environmental Interest Group Behavior and Self-Selection Bias in Contingent Valuation Mail Surveys     

JOHN C. WHITEHEAD 《Growth and change》1991,22(1):10-20

This paper analyzes the behavior of a general sample and an environmental interest group sample in a contingent market for wetlands preservation. Mail survey response rates and environmental values for wetlands preservation are significantly greater in the environmental interest group sample than in the general population sample. An estimate of the potential self-selection bias in the benefits of wetlands preservation is made. These results suggest that self-selection bias in contingent valuation mail surveys could upwardly bias aggregate benefit estimates as much as 50 percent. Potential, but costly, solutions to the problem of self-selection bias are suggested.  相似文献   

In vitro Maturation of Oocytes from Santa Ines Ewes Subjected to Consecutive Sessions of Follicular Aspiration by Laparoscopy     

LC Padilha  PPM Teixeira  EA Pires‐Buttler  M Apparício  TF Motheo  PAP Savi  EYO Nakaghi  AE Alves  WRR Vicente 《Reproduction in domestic animals》2014,49(2):243-248

The success of embryo production in vitro depends upon the use of an efficient oocyte retrieval technique, and the best results have been obtained by laparoscopic aspiration. The aim of this study was to evaluate the effect of consecutive sessions of follicular aspiration on the quantity, quality and in vitro maturation competence of oocytes obtained from ewes subjected to hormonal stimulation. Six Santa Ines ewes underwent nine sessions of follicular aspiration by laparoscopy with a 7‐day interval between sessions, totalling 56 aspirations. After 24 h of culture, oocytes were stained and classified according to the stage of nuclear and cytoplasmic maturation. Oocyte retrieval rate was 61.4 ± 2%, resulting in a total of 249 oocytes. No significant variation was observed between sessions (p > 0.05). The average number of oocytes retrieved from each ewe was 6.4 ± 2 per session and 42 ± 4 in total. No significant difference was observed between the frequencies of the different stages of nuclear maturation: 32.72% mature, 40.74% immature and 26.54% degenerated/indeterminate oocytes; however, a significant difference was observed between the frequencies of the different stages of cytoplasmic maturation: 10.7% mature, 73.25% immature and 16.05% degenerated/indeterminate oocytes. No significant difference was observed in nuclear or cytoplasmic maturation between the weeks of procedure. We conclude that after nine consecutive sessions of follicular aspiration, the quantity and quality of retrieved oocytes remained unchanged as well as the levels of nuclear and cytoplasmic maturation obtained, demonstrating the viability of this technique for repetitive follicular aspirations on the same donor.  相似文献   

Net ecosystem carbon exchange for Bermuda grass growing in mesocosms as affected by irrigation frequency     

Yuan LI  Gabriel Y. K. MOINET  Timothy J. CLOUGH  John E. HUNT  David WHITEHEAD 《土壤圈》2022,32(3):393-401

Intensification of grazed grasslands following conversion from dryland to irrigated farming has the potential to alter ecosystem carbon (C) cycling and affect components of carbon dioxide (CO₂) exchange that could lead to either net accumulation or loss of soil C. While there are many studies on the effect of water availability on biomass production and soil C stocks, much less is known about the effect of the frequency of water inputs on the components of CO₂ exchange. We grew Bermuda grass (Cynodon dactylon L.) in mesocosms under irrigation frequencies of every day (I₁ treatment, 30 d), every two days (I₂ treatment, 12 d), every three days (I₃ treatment, 30 d), and every six days (I₆ treatment, 18 d, after I₂ treatment). Rates of CO₂ exchange for estimating net ecosystem CO₂ exchange (F_N), ecosystem respiration (R_E), and soil respiration (R_S) were measured, and gross C uptake by plants (F_G) and respiration from leaves (R_L) were calculated during two periods, 1–12 and 13–30 d, of the 30-d experiment. During the first 12 d, there were no significant differences in cumulative F_N (mean ±standard deviation, 61 ±30 g C m^-2, n = 4). During the subsequent 18 d, cumulative F_N decreased with decreasing irrigation frequency and increasing cumulative soil water deficit (W), with values of 70 ±22, 60 ±16, and 18 ±12 g C m^-2 for the I₁, I₃, and I₆ treatments, respectively. There were similar decreases in F_G, R_E, and R_L with increasing W, but differences in R_S were not significant. Use of the C₄ grass growing in a C₃-derived soil enabled partitioning of R_S into its autotrophic (R_A) and heterotrophic (R_H) components using a ¹³C natural abundance isotopic technique at the end of the experiment when differences in cumulative W between the treatments were the greatest. The values of R_H and its percentage contributions to R_S (43% ±8%, 42% ±8%, and 8% ±5% for the I₁, I₃, and I₆ treatments, respectively) suggested that R_H remained unaffected across a wide range of W and then decreased under extreme W. There were no significant differences in aboveground biomass between the treatments. Nitrous oxide (N₂O) emission was measured to determine if there was a trade-off effect between irrigation frequency and increasing W on net greenhouse gas emission, but no significant differences were found between the treatments. These findings suggest that over short periods in well-drained soil, irrigation frequency could be managed to manipulate soil water deficit in order to reduce net belowground respiratory C losses, particularly those from the microbial decomposition of soil organic matter, with no significant effect on biomass production and N₂O emission.  相似文献   

Nongovernmental Organizations and the Option Value of Donated Land     

CATHERINE M. CHAMBERS  PAUL E. CHAMBERS  JOHN C. WHITEHEAD 《Growth and change》1995,26(3):442-462

ABSTRACT Nongovernmental organizations frequently receive donations of land that have unknown characteristics. This paper presents an analytical model of the option to preserve such land. The nongovernmental organizations' option value arises from the option to preserve or sell the land to generate funds for other preservation projects. We show that die preservation option is equivalent to an option that allows the nongovernmental organization to choose between he maximum of the market value of the land and the preservation value of the land. From the resulting closed from solution of the option to preserve, we perform comparative statics showing how the relevant factors (preservation value of the land, the development value of the land, the length of the that the option is available, and the uncertainty surrounding the relative values of preservation and development) influence the value of the preservation option. In addition, to the basic model, we present three model modifications. The first examines the effects of costly preservation and costly nonpreservation. In the second extension, we examine the effects of freeriding modeled by a continuous variable. In the final modification, we relax the assumption of the fixed survey period and show the optimal development date.  相似文献   

The fate at several time intervals of ¹⁵N-labelled ammonium nitrate applied to an established grass sward     

A. W. BRISTOW  J. C. RYDEN  D. C. WHITEHEAD 《European Journal of Soil Science》1987,38(2):245-254

¹⁵N-labelled ammonium nitrate solution was applied in late April to circular, enclosed micro-plots prepared by pressing open-ended polypropylene cylinders into an established sward of perennial ryegrass. Cylinders were removed from the ground at intervals between 2 and 370 days after the application and assessments made of the distribution of ¹⁵N in plant and soil components. Of the added labelled N, 54.7% was recovered in the herbage which was cut four times during the growing season and again at the final sampling date. After two days, 37% of the labelled N was recovered in the soil microbial biomass. Large fluctuations occurred in the amount of ¹⁵N recovered in the soil microbial biomass over the next 14 days suggesting that rapid cycling of ¹⁵N occurred between this fraction and the mineral N fraction. After the first cut in late May, translocation of¹⁵N occurred more slowly from the roots into the stubble than from stubble into new herbage, so that the amount in the stubble declined more rapidly than did that in the roots. During the winter, there was no net transfer of N from the roots to above-ground components of the sward. By the end of the growing season, half the ¹⁵N remaining in the sward was immobilized in the humified fraction of the soil organic matter; some of this was mineralized in the following spring.  相似文献