Australia's forests and woodlands have been extensively cleared since European settlement. Cropping regions have the least retained native vegetation, with the greatest depletion of forests and woodlands being observed in Western Australia and South Australia. Salinisation, erosion and landslides have resulted from excessive clearing and inappropriate tree removal from particular units within the landscape. Major problems in cropping regions are the dramatic reduction in total woody cover and the fragmentation of retained vegetation into isolated remnant patches which tend to be very small (<10–15 ha). Those states with little remnant vegetation have legislation which restricts further clearing and the main emphasis is on managing remnant patches for conservation. For those states with a large proportion of woody vegetation uncleared, the main priority is to ensure that past mistakes are not repeated and that any vegetation clearance is based upon sound ecological principles.Throughout Australia, the condition of the remaining vegetation is of great concern and management guidelines for both conservation and production are being sought. Clearing may lead directly to soil erosion, but often the cause of erosion is inappropriate post-clearing management. Overgrazing is a major cause of vegetation and soil degradation, particularly in semi-arid regions.An understanding of the complex inter-relationship between woody vegetation, grazing and fire is necessary if 1) flora and fauna are to be conserved; 2) hydrological balance is to be maintained; and 3) rural industries are to remain viable. Planning at the catchment level is necessary to implement strategies to meet conservation and hydrological goals. Within that framework, individual property planning must include consideration of the area of native woody vegetation to be retained and its configuration. In many cases, the purpose of retention will influence the decisions of where and how native vegetation should be retained. 相似文献
Imbalances in the proliferation and apoptosis processes are involved in numerous epithelial alterations. In the seminiferous epithelium, normal spermatogenesis is regulated by spermatogonia proliferation and germ cell apoptosis, and both processes are involved in diverse pathological alterations of the seminiferous epithelium. Other physiological phenomena including aging and short photoperiod, in which apoptosis and proliferation seem to play important roles, cause testicular changes. Aging is accompanied by diminished proliferation and increased apoptosis, the latter occurring in specific states of the seminiferous cycle and considered the cause of epithelium involution. However, there is no clear evidence concerning whether proliferation decreases in the spermatogonia themselves or is due to an alteration in the cell microenvironment that surrounds them. As regards the factors that regulate the process, the data are scant, but it is considered that the diminution of c‐kit expression in the spermatagonia, together with the diminution in antiapoptotic factors (Bcl‐xL)) of the intrinsic molecular pathway of apoptosis play a part in epithelial regression. A short photoperiod, especially in rodents, produces a gradual involution of the seminiferous epithelium, which is related with increased apoptosis during the regression phase and a diminution of apoptosis during recrudescence. Proliferative activity varies, especially during the total regression phase, when it usually increases in the undifferentiated spermatogonia. In other species showing seasonal reproduction, however, decreased proliferation is considered the main factor in the regression of the seminiferous epithelium. Little is known about how both phenomena are regulated, although data in rodents suggest that both the intrinsic and extrinsic pathways of apoptosis contribute to the increase in this process. In conclusion, regression of the seminiferous epithelium in physiological situations, as in many pathological situations, is a result of alterations in equilibrium between the proliferation and apoptosis of germinal cell types. However, both physiological phenomena showed important differences as regard proliferation/apoptosis and their regulation pathways, probably as a result of their irreversible or reversible character. 相似文献
Malocclusions are a misalignment or incorrect positioning of the teeth when the upper and lower jaws close. These are poorly described in the koala and can result in irregular mastication which can have lifelong effects on body condition and oral health. A total of 370 koalas from two populations in Queensland (295) and one in South Australia (75) were examined for malocclusions. The prevalence of malocclusions in South Australian free‐ranging koalas, captive Queensland koalas and Queensland free‐ranging koalas was 39% (44), 30% (29) and 22% (29) respectively. Four types of malocclusion were identified based on severity of misalignment of the incisor/canine region, types 1, 2, 3 and 4. Maxillary overbite measurements of the molariform teeth were determined and these anisognathic values were then used to describe malocclusions within familial relationships in captive colonies. Captive koalas with a malocclusion had narrower mandibular width that ranged between 0.5 and 1% less than the normal measurements. The specific malocclusions reported in this study affected individuals by leading to tooth rotation, mobility and erosion with inefficient mastication of food and vegetation compaction. These changes increased the oral cavity pathology, by placing animals at risk of periodontal disease. There was evidence of familial links to malocclusion types in captive animals. Therefore captive breeding recommendations should consider known koala malocclusion traits to minimise their effect on future generations. 相似文献
AIMS: The principle aim of this study was to examine the association between infection with Theileria orientalis Ikeda type and growth rates of suckled beef calves on four beef farms. In addition, associations between calf sex, sampling time, and individual farm and T. orientalis Ikeda type infection intensity and haematocrit (HCT) were investigated.
METHODS: The study was a prospective longitudinal study in which 240 calves from four purposively selected beef farms in the North Island of New Zealand were blood sampled and weighed in late spring, mid-summer and early autumn. Two farms were from high-risk (A and B) and two from low-risk (C and D) tick areas. Blood samples were analysed to determine HCT, and the number of T. orientalis Ikeda type organisms/µL of blood (infection intensity) using a quantitative PCR assay. A calf was defined as infected if >415 organisms/µL were detected in a blood sample. Linear mixed models were used to examine associations between infection intensity, mean daily liveweight gain (MDG), HCT, calf sex and time of sampling on the four farms.
RESULTS: On Farms A and B nearly all calves were infected at each sampling time, on Farm C <30% were infected at any sampling and on Farm D infection prevalence increased from 32 to 79% between late spring and early autumn. On Farms C and D, from mid-summer to early autumn, mean MDG was 0.127 (95% CI=0.072–0.183) kg/day less for infected than uninfected calves (p<0.001). On all farms MDG was negatively associated with infection intensity for mid-summer and early autumn sampling times (p=0.037). The relationship between time of sampling and infection intensity varied between farms (p<0.001), and between male and female calves (p=0.018). Females had a higher infection intensity than males at the mid-summer and early autumn samplings. The association between HCT and infection intensity varied with sampling time and farm (p=0.018). There was a strong negative association between infection intensity and HCT at the late spring sampling, but in mid-summer there was no association, and in early autumn only a weak association.
CONCLUSIONS AND CLINICAL RELEVANCE: This study has shown that beef farmers in the North Island of New Zealand should be concerned about the welfare effects and economic impacts of T. orientalis Ikeda type infection in suckled beef calves. 相似文献
AIMS: To assess the efficacy of praziquantel (PZQ) administered to control helminths in captive-reared critically endangered black stilts (Himantopus novaezelandiae) before their release into the wild and determine the effect on their survival shortly after release.
METHODS: Of 77 captive black stilts, 37 were treated with PZQ prior to release into the wild in South Canterbury, New Zealand, in August and September 2007. Faecal helminth egg counts (FEC) were measured before and after anthelmintic treatment, and before and after release to the wild using modified faecal flotation and sedimentation methods. In addition, total helminth counts were determined in 11 of the birds that died following release, as well as four captive and 11 other wild stilts.
RESULTS: The efficacy of PZQ against trematodes was 92% and against Capillaria spp. was 34%. No trematode or Capillaria spp. eggs were detected in treated birds 1 day after treatment, but FEC increased 3–5 days after treatment. There were no differences in the total helminth counts for trematodes, cestodes or Capillaria spp. in control or treated birds (p>0.2). Survival did not differ between treatment groups in the August or September releases (p>0.4). Of control and treated birds, 11/17 (65%) and 8/14 (57%) survived to 31 days, respectively, in the August release, and 16/20 (80%) and 10/15 (67%) survived to 84 days, respectively, in the September release.
CONCLUSION: Overall, the results suggest that PZQ treatment may be an unnecessary cost and the risks of producing anthelmintic resistance, injuring the birds during processing or producing an unnecessary stress response at the time of release could exceed any likely benefits.
CLINICAL RELEVANCE: It is recommended that pre-release anthelmintic treatment of black stilts should be used only if indicated by health screening. Any treatment should incorporate annual efficacy testing to monitor the emergence of anthelmintic resistance. 相似文献
An 18-year-old Friesian stallion was examined approximately one week after reportedly presenting scrotal swelling due to torsion of the spermatic cords. Upon presentation no scrotal swelling was noted, the testes were normally oriented, and no abnormalities of the spermatic cords were noted. However, both testes were smaller than expected for a mature stallion and deep palpation revealed that the consistency of the testes was nodular. Ultrasonographic evaluation of the testes revealed diffuse heterogeneous parenchyma with multiple hypoechoic nodular areas. Grossly, the testicular parenchyma was effaced by multiple gray-tan nodules of varying consistency interspersed with gray-white bands of tissue. Microscopic analysis revealed multiple pleomorphic neoplastic foci disseminated throughout both testes. Histological and immunohistochemical features were atypical and consistent with the diagnosis of bilateral testicular mixed germ cell-sex cord stromal tumours. Bilateral testicular tumours and testicular mixed cell tumours are extremely rare in stallions and this is the first report of bilateral testicular mixed germ cell-sex cord-stromal tumours in a stallion. Our findings indicate that certain ultrasonographic characteristics are suggestive of testicular tumour and that immunohistochemistry markers can be used to better characterize testicular neoplasms in stallions. 相似文献
A 5‐year‐old Arabian stallion was managed for breeding with fresh/extended semen during a period of 8 months with a resulting per cycle pregnancy rate of 26.3%. The stallion was in good health and no abnormalities of the reproductive tract were observed. Evaluation of several ejaculates revealed that sperm production and semen quality were mostly unchanged during the period of evaluation, that sperm production was normal and that semen quality was extremely poor. The most prevalent sperm defects were abnormal heads and mid‐pieces. Most abnormal heads were microcephalic and/or tapered and considerable variation in sperm head dimensions within and among ejaculates was observed. A unique defect characterized by swollen/roughened mid‐piece caused by accumulation of cytoplasmic‐like material and abnormal mitochondrial sheath was observed. Nuclear vacuoles, acrosome defects, and teratoids were also prevalent and most sperm presented multiple abnormalities. The absence of any clear cause or any signs of testicular degeneration, combined with normal sperm production, and constant abnormal sperm production suggest an inherent, congenital disturbance of spermatogenesis as the cause of teratospermia in this case. 相似文献
