黄土耕作坡面溅蚀过程中微地形响应特征

[目的]探究60mm/h雨强下不同耕作坡面在溅蚀阶段的微地形变化特征,为黄土坡地水土保持耕作方式布设提供科学依据。[方法]在室内人工模拟降雨试验的基础上,采用激光扫描量测方法分别获取溅蚀前后4种不同耕作方式(人工锄耕、人工掏挖、等高耕作、耙磨整平)黄土坡面微地形相对高程,并对能反映微地形变化的高精度M-ΔDEM进行了分析。[结果]不同耕作措施下坡面微地形均具有较弱的空间变异,其空间分异主要受耕作措施的影响;降雨对微地形具有一定的夷平效应,且不同耕作坡面在1~1.3m尺度范围内均表现出侵蚀平衡现象;不同耕作微地形对溅蚀均具有阻滞作用,其中人工掏挖和等高耕作具有较强的水土保持作用。[结论]微地形水系分维能较好地反映复杂的微地形特征,而坡面耕作方式是溅蚀过程中微地形时空变异分布状况的控制性因子。     

ADCC and complement-dependent lysis as immune mechanisms against EHV-1 infection in the horse

Immunity to equine herpesvirus type 1 (EHV-1) was evaluated using sera collected from yearling horses involved in a trial of a commercial vaccine. Measurement of the ability of these sera to mediate antibody-dependent cellular cytotoxicity and complement-dependent lysis revealed that these mechanisms, although potentially important in recovery from EHV-1 infection, do not play a role in protection following vaccination.     

Clinical and laboratory findings in cats infected with feline immunodeficiency virus

Thirty-two cats referred to the Feline Studies Centre between June 1987 and October 1988, and 14 in-contact cats, were found to be infected with feline immunodeficiency virus. Most of the 46 cats were non-pedigree and free ranging; 27 were male (19 neutered) and 19 were female (18 neutered). Their ages ranged from one to 17 years and the average age was 5.8 years. The most common clinical signs were lethargy, inappetence, weight loss, pyrexia and lymphadenopathy; most cases had multiple abnormalities. Other common signs were gingivitis, diarrhoea, rhinitis and ocular discharge. Eight cats had neoplasia. The commonest haematological abnormalities were anaemia, neutropenia, lymphopenia and monocytosis. Eight cats had lymphocytosis; seven of these were in a single house-hold. Several cats had high serum globulin levels and half of those tested had high IgG levels. Seven cats had no detectable antibody to feline immunodeficiency virus even though the virus was cultured from the peripheral blood lymphocytes. During follow-up for up to 60 weeks one cat died and 23 were destroyed on humane grounds.     

Cellular content of secretions obtained by lavage from different levels of the equine respiratory tract

Lavage procedures were used to obtain samples of respiratory secretions from the nasal cavity, trachea, bronchi and bronchoalveolar level of apparently normal conscious horses, and the cellular composition of the lavage fluids was assessed. There was a progressive increase in total cell count of the secretions obtained from the upper to the lower respiratory tracts. Nasal lavage fluid was composed chiefly of epithelial cells, whereas tracheal, bronchial and bronchoalveolar fluids contained higher proportions of macrophages, lymphocytes and neutrophils. Eosinophils and mast cells were identified in small numbers. The results of the differential cell counts were compared with previous published reports, which revealed some major differences between studies. It is suggested that these differences may relate to variations in the collection technique, the cytological interpretation of cell types, the presence of subclinical airway disease, and the degree of exposure to airborne environmental contaminants.     

Maturation of cellular defence in the respiratory tract of young calves

The maturation of respiratory tract defence was investigated in a longitudinal study of calves during the first 100 days of life. From day 7, the proportions of the cell types identified in bronchoalveolar lavage (BAL) fluid were similar to those found in adults, with a predominance of alveolar macrophages over polymorphonuclear neutrophils (PMNs) and lymphocytes. Functionally, bactericidal activity of BAL cells was defective and for the first 21 days they supported intracellular bacterial growth. At 24 hours of life, the movement of peripheral blood neutrophils to a chemotactic source was poor, but this increased rapidly during the first week of life. Like BAL cells, peripheral blood PMNs supported intracellular bacterial growth for the first two weeks of life. These studies suggest that cellular defence mechanisms may be compromised during the first week of life.     

The intestinal and serum humoral immune response of mice to systemically and orally administered antigens in liposomes: I. The response to liposome-entrapped soluble proteins.

The development of oral vaccines is of great importance in veterinary medicine and new adjuvants and carriers are essential to this aim. Liposomes are effective systemic adjuvants but the relatively little data on their potential as oral adjuvants is inconclusive. Liposomes containing ovalbumin (OA) were effective adjuvants when administered intraperitoneally to mice. Feeding mice with OA or keyhole limpet haemocyanin in liposomes in a series of priming and boosting regimes failed to elicit any significant increase in serum or intestinal antibody response compared with feeding the free antigen. Oral tolerance induction to systemic challenge was also unaffected by OA entrapment in liposomes. In vitro liposome stability assays at 37 degrees C demonstrated a substantial resistance to disruption in the presence of acidic stomach contents. However, the addition of bile caused a rapid and profound release of protein marker from the liposomes. The rate and degree of disruption was influenced by the type of phospholipid used. These results suggest that liposomes may be useful as carriers for orally administered compounds but they are ineffective as adjuvants for the non-particulate, naturally weak immunogens used in this study.     

Technique for physiological examination of canine skeletal muscle in vivo

A technique is described for studying the physiological function of canine skeletal muscle in vivo. The contractile properties of the tarsal flexor muscles were examined in three beagle dogs under general anaesthesia. The force responses to electrical stimulation of the common peroneal nerve were measured at various frequencies to determine the frequency:force relationship for this muscle group. Fatigue characteristics were also examined during intermittent stimulated activity delivered in a set pattern of frequencies. The results provide quantitative characterisation of muscle function which is repeatable. The technique described could be applied to other animals and is a potentially powerful tool for evaluating the effects of drugs on muscle performance.     

Macrophage clearance of 125I-labelled polyvinyl pyrrolidone in the horse: effect of ovarian steroids and persistent endometritis

The rate of clearance of 125I-labelled polyvinyl pyrrolidone (PVP) from blood was measured in mares as an indicator of macrophage function. In three out of four cycling mares, PVP clearance was slower during oestrus than dioestrus. Similarly, administration of oestrogen to four ovariectomised mares tended to depress PVP clearance compared with clearance from the same mares before they received oestrogen. However, the effect of oestrogen was not statistically significant. Mares susceptible to persistent endometritis had rates of PVP clearance which were similar to those of genitally normal mares.