The effects of herbaceous and woody competition on planted white pine in a clearcut site

We investigated the effects of herbaceous and woody vegetation control on the survival and growth of planted eastern white pine (Pinus strobus L.) seedlings through six growing seasons. Herbaceous vegetation control involved the suppression of grasses, forbs, ferns, and low-shrubs, and was maintained for 0, 2, or 4 years after white pine seedlings were planted. Woody control involved the removal of all tall-shrub and deciduous trees, and was conducted at the time of planting, at the end of the second or fifth growing seasons, or not at all. Seedling height and basal diameter responded positively and proportionally to duration of herbaceous vegetation control. Gains associated with woody control were generally not significant unless some degree of herbaceous vegetation control was also conducted. Only herbaceous control increased pine crown closure and rate of crown closure. Herbaceous control and the presence of 5000–15,000 stems per ha of young overtopping aspen were associated with reduced weevil (Pissodes strobi Peck.) injury and increased pine height growth. The study suggests that white pine restoration strategies on clearcut sites should focus on the proactive, early management of understory vegetation and the gradual reduction of overtopping cover from woody vegetation to create a seedling light environment that supports acceptable growth with minimal weevil damage.     

Functional and ultrastructural changes in neutrophils from mares and foals experimentally inoculated with a respiratory tract strain of equine herpesvirus-1

Neutrophils isolated from venous blood of adult and foal ponies inoculated with equine herpesvirus-1 were evaluated by in vitro function tests and by electron microscopy. Foals had fever and severe neutropenia 24 hours after inoculation; increased neutrophil random migration under agarose and decreased antibody-dependent cell-mediated cytotoxicity were significant at 24 hours, but values had returned to preinoculation levels by 72 hours. Mares had fever and leukopenia of less severity, increases in neutrophil migration, and longer persistence of primary granule release than were seen in foals. Reduced migration and degranulation, and a decrease in antibody-dependent cell-mediated cytotoxicity seen with neutrophils from foals, as compared with mares, may relate to the high susceptibility of foals to equine herpesvirus-1 infection.     

Pathogenicity of equine herpesvirus 1 subtype 2 for foals and adult pony mares

Three pony mares and 4 pony foals were inoculated with a subtype 2 strain of equine herpesvirus 1. Foals had periods of fever 12 h and 2.5 days after inoculation and leukopenia, involving both neutrophils and lymphocytes, followed by leukocytosis. Mares had transient fever and leukopenia 24 hours after inoculation that were less severe than in foals. An increase in circulating virus-neutralizing antibody was seen in 2 of 3 inoculated mares, but not in foals. Attempts to isolate virus from blood were unsuccessful. These studies show that equine herpesvirus 1 subtype 2 is a mild pathogen for ponies and infection may result in inapparent clinical disease.     

The relationship between appetite and plasma non-esterified fatty acid levels in housed calves

Non-esterified fatty acid (NEFA) levels in housed, 3-month-old calves were monitored in two experiments designed to establish (i) the effect of diet and time of sampling in relation to feeding on blood levels; and (ii) the relationship between appetite and plasma NEFA in animals on chopped hay. In the first experiment, a significant drop in NEFA levels was recorded after feeding. Furthermore, the NEFA levels of calves maintained on concentrate were significantly lower than those on hay throughout the post-feeding period. In the second study, a significant negative correlation was established between NEFA levels and intake of chopped hay in (i) ad-lib-fed calves infected with the abomasal nematode Ostertagia ostertagi; (ii) worm-free animals pair-fed with those in group (i); and (iii) ad-lib-fed worm-free calves. Regression analysis of raw and transformed data from all three groups combined also yielded significant correlations. It is suggested that the measurement of blood NEFA may be a useful indirect indicator of feed intake in conditioned housed calves offered hay diets.     

Pathologic changes associated with brucellosis experimentally induced by aerosol exposure in rhesus macaques (Macaca mulatta)

OBJECTIVE: To develop an aerosol exposure method for induction of brucellosis in rhesus macaques (Macaca mulatta). ANIMALS: 10 adult rhesus macaques. PROCEDURE: 8 rhesus macaques were challenge exposed with 10(2) to 10(5) colony-forming units of Brucella melitensis 16M by use of an aerosol-exposure technique, and 2 served as control animals. All macaques were euthanatized 63 days after challenge exposure. Gross and microscopic lesions, bacterial burden in target organs, and histologic changes in tissues were evaluated. RESULTS: Grossly, spleen weights were increased in exposed macaques, compared with spleen weights in control macaques. Histologically, there was inflammation in the liver, kidneys, spleen, testes, and epididymides in exposed macaques. The spleen and lymph nodes had increased numbers of lymphohistiocytic cells. Morphometrically, the spleen also had an increased ratio of white pulp to red pulp. Areas of hepatitis and amount of splenic white pulp increased with increasing exposure dose. CONCLUSIONS AND CLINICAL RELEVANCE: Pathologic findings in rhesus macaques after aerosol exposure to B melitensis are similar to those observed in humans with brucellosis. IMPACT FOR HUMAN MEDICINE: These results may aid in the development of a vaccine against brucellosis that can be used in humans.     

An estimate of specificity for a Johne's disease absorbed ELISA in northern Australian cattle

OBJECTIVE: To estimate the specificity of an absorbed enzyme-linked immunosorbent assay kit for Johne's disease (JD) when used in mature cattle populations resident in northern Australia. DESIGN: Blood samples were collected from beef cattle in northern Queensland, the Northern Territory and northern Western Australia, and from dairy cattle in northern Queensland. The specificity of a serological test for JD was estimated by testing the blood samples with an absorbed ELISA kit. Further samples were collected from cattle with positive ELISA results to determine the presence or absence of infection with Mycobacterium avium subsp paratuberculosis. PROCEDURE: During 1995 and 1996, blood, tissue and gut contents were collected from beef cattle at abattoirs in Queensland and the Northern Territory; and blood and faecal samples were collected from dairy cattle in herds assessed to be most at risk for JD in northern Queensland. The blood samples were tested using an absorbed ELISA kit. Tissues and gut contents from beef cattle that had positive ELISA results were cultured for M. avium subsp paratuberculosis, and tissues were examined histologically. Faecal samples from dairy cattle with positive ELISA results were cultured for M. avium subsp paratuberculosis. RESULTS: Estimates of specificity for this absorbed ELISA in mature northern Australian cattle were 98.0% (97.0 to 98.8%, 95% CI) in beef cattle, and 98.3% (96.7 to 99.3%, 95% CI) in dairy cattle. CONCLUSION: Estimates of specificity in this study were lower for beef cattle from the Northern Territory and northern Western Australia and for dairy cattle from northern Queensland than those quoted from studies on cattle in southern Western Australia. This should be considered when serological testing using the JD ELISA is carried out on northern Australian cattle.     

Intravascular macrophages in lungs of pigs infected with Haemophilus pleuropneumoniae

Pigs were inoculated intratracheally with a virulent or an avirulent isolate of Haemophilus pleuropneumoniae serotype 5 and sacrificed during the first 24 hours post-inoculation. Intravascular macrophages were examined by electron microscopic and morphometric techniques. Samples of lung were taken from regions with no macroscopic lesions (Zone 0), 2.5 to 3.0 cm from lesions (Zone 1), and from the immediate edge of lesions (Zone 2). Those pigs inoculated with the avirulent isolate did not develop lesions. Pigs given the virulent isolate consistently developed necrohemorrhagic lesions in the dorsolateral aspect of the caudal and middle lung lobes. Relative volumes of intravascular macrophages in Zones 1 and 2 increased with increased time post-inoculation; in pigs given the avirulent isolate, intravascular macrophage volume decreased with increased time post-inoculation. Cytoplasmic volume to nuclear volume ratios for macrophages in Zone 2 from pigs with necrohemorrhagic lesions progressively increased with increased time post-inoculation. Enlarged intravascular macrophages had large nuclei, prominent nucleoli, and abundant cytoplasm. Increased cytoplasmic volume was the result of increased numbers of lysosomes, phagosomes, rough and smooth endoplasmic reticulum, and large Golgi complexes. Pigs inoculated with the virulent bacteria had IV macrophages with large phagosomes that contained necrotic cell debris and fibrin. Macrophages with phagosomes were more frequent in the 6-, 9-, and 24-hour sample periods of pigs with lesions than in any other group. Intercellular adhesion plaques (ICAP) were present between IV macrophages and subjacent endothelial cells. ICAP's increased in length with increased time post-inoculation in Zones 1 and 2 from pigs with necrohemorrhagic lesions. In later sample periods, multiple closely associated and interlacing IV macrophages formed a discontinuous layer over endothelial cells in Zone 2 samples near necrohemorrhagic lesions. These results suggest that the intravascular macrophage population changes from immature macrophages to mature macrophages or immature epithelioid cells within 24 hours after inhalation of a virulent Haemophilus pleuropneumoniae. Furthermore, intravascular macrophages likely function to clear cellular and acellular debris from the blood in pneumonic conditions.