维生素营养的新概念

动物的维生素需要量是动态的 ,是随其基因型、生产性能高低、所用生产体系的不同而不同的 ,还随着人们对维生素功能更加深入的了解而不同。这意味着 ,维生素推荐量和维生素添加指南都需要经常更新。现在已经有了新的指南 ,其中的推荐量是根据“最佳维生素营养”的长期概念加以更新的 ,这有助于营养师保证动物的健康和性能目标不因维生素供应量的问题而受害。只有当动物有效利用了为生长、健康、繁殖和存活而通过日粮提供的养分以后才算是实现了最佳营养。虽然所有的养分 ,如蛋白质、矿物质和水 ,对于动物的功能都极为重要 ,但维生素却另有其…     

Long-term vegetational history of a Picea abies stand in south-eastern Norway: Implications for the conservation of biological values

The development of a forest stand in south-eastern Norway during the last 9000 years is investigated by pollen and charcoal analyses. The aims are to identify factors that have influenced current biodiversity, which includes the lichen Usnea longissima, and examine the immigration and establishment of the current dominant tree Picea abies. Fire has been a variable but major disturbance factor at the site throughout the study period but has ceased during the last 100 years. Picea immigration was primarily a natural process but local establishment occurred after a major disturbance. Cultural impact began 3500 years ago during the Bronze Age, but was most intensive between AD 1600 and AD 1900. It led to the local extinction of deciduous trees and created a biodiversity bottleneck that facilitated the rise to dominance of Picea. Guidelines are proposed for future management designed to preserve and enhance local biological values.     

Quantitative assessment of nociception in horses by use of the nociceptive withdrawal reflex evoked by transcutaneous electrical stimulation

OBJECTIVES: To evoke and measure the nociceptive withdrawal reflex (NWR) by use of electromyographic recordings and to score the behavioral nociceptive responses to electrical pulses in standing nonsedated horses. ANIMALS: 10 adult horses. PROCEDURE: The lateral palmar digital nerve of the forelimb was transcutaneously stimulated, and surface electromyographic responses were recorded from the ulnaris lateralis, extensor carpi radialis, and common digital extensor muscles. Stimuli consisted of a 25-millisecond train of 5 constant-current pulses delivered by a computer-controlled stimulator. The 80- to 250-milliseconds poststimulation interval was analyzed to detect the NWR. The current intensity was increased in steps of 0.5 mA until the NWR threshold intensity (lt) was reached. The stimulus at It was repeated twice. Latency and amplitude of the NWR, together with the behavioral reaction of horses, were analyzed. The latter was scored according to a scale from 0 (no reaction) to 5 (vigorous reaction). Finally, 3 suprathreshold stimuli at 1.2 X It were analyzed. RESULTS: The median It to elicit NWR was 2.5 mA. Median onset latency of the NWR was 96.0 milliseconds at It and 89.6 milliseconds for suprathreshold stimuli. The amplitude of the reflexes was higher for suprathreshold stimulations, and behavioral reactions were slightly stronger when stimulus intensity increased. CONCLUSIONS AND CLINICAL RELEVANCE: Results of our study indicate that it is possible to record NWR in conscious standing horses, to define a reflex threshold, and to measure reflexes in response to increasing stimulus intensity.     

How representatively can we sample soil mineral nitrogen?

Spatial distribution of soil mineral‐N content (N_min) is a scale‐variant process. Precision farming assumes knowledge about the spatial distribution of N_min. Moreover, sampling in management zones is based on the assumption of spatial dependence between sampling points. In the present study, variability structure of N_min and the sources of variability were investigated. Within an agricultural landscape, N_min was investigated across a field in a nested design over four consecutive years. Temporally unstable structure of individual nests require a sampling with several nests in the field. In the investigated field, 35%–49% of the total variability derived from small‐scale variability observed at spatial distances of <5 m and from sampling and analytical errors. Differences between 10 and 26 kg N ha^–1 for the soil depth increment 0–60 cm can be expected. Uncertainty due to analytical errors were in the order of 5–10 kg N ha^–1 for a 0–60 cm layer.     

Contribution of fallow periods between rice crops to seasonal GHG emissions: effect of water and tillage management

ABSTRACT

Irrigated rice cultivation is a major source of greenhouse gas (GHG) emissions from agriculture. Methane (CH₄) and nitrous oxide (N₂O) are emitted not only throughout the growing season but also in the fallow period between crops. A study was conducted for two transition periods between rice crops (dry to wet season transition and wet to dry season transition) in the Philippines to investigate the effect of water and tillage management on CH₄ and N₂O emissions as well as on soil nitrate and ammonium. Management treatments between rice crops included (1) continuous flooding (F), (2) soil drying (D), (3) soil drying with aerobic tillage (D + T), and (4) soil drying and wetting (D + W). The static closed chamber method was used to measure CH₄ and N₂O fluxes.

Soil nitrate accumulated and N₂O was emitted in treatments with soil drying. Nitrate disappeared while ammonium gradually increased after the soil was flooded during land preparation, indicating net nitrogen mineralization. N₂O emissions were highest in both transition periods in D + W (437 and 645 µg N₂O m^?2 h^?1). Methane emissions were significant in only the F treatment. The highest global warming potential (GWP) in the transition between rice crops occurred in F, with CH₄ contributing almost 100% to the GWP. The GWP from other treatments was lower than F, with about 60–99% of the GWP attributed to N₂O emissions in treatments with soil drying. The GWP in the transition between rice crops represented up to 26% of the total GWP from harvest to harvest. This study demonstrates that the transition period can be an important source of GHG emissions with relative importance of CH₄ and N₂O depending on the soil water regime. Therefore, the transition period should not be disregarded when estimating GHG emissions for rice cropping systems.     

Migration Inhibition Studies on Peripheral Leukocytes and Lymph Node Cells from Ruminants with Fascioliasis

Delayed type hypersensitivity against antigens of Fasciola hepatica has been repeatedly documented in infected hosts. Evidence has been presented to suggest that the delayed reactivity may develop earlier in the regional lymph nodes of the parasitized organ than in other lymph nodes of the body (Soulsby 1971).     

Deposition characteristics and biological effectiveness of fungicides applied to winter wheat and the hazards of drift when using different types of hydraulic nozzles

Hydraulic-fan cone, low-pressure fan and two-chamber cone nozzles were used at 1.5, 3.0 and 6.0 bar (150, 300 and 600 kPa) to deliver 140, 200 and 3001 ha⁻¹ respectively of a fungicide spray to control mildew and yellow rust in winter wheat. No significant differences in biological effect were obtained although fan nozzles deposited significantly more on the upper parts of the stems, and two-chamber cone nozzles deposited less on the flag leaf and on the upper part of the stems. Because of their higher deposit and more even distribution, fan nozzles should be preferred, operated at a pressure of 1.5–3 bar to deliver a spray volume of 140–190 lha⁻¹ at 7 km h⁻¹ and to obtain an acceptable biological effect. Higher pressure (6 bar) and volume rates gave no improvement in fungicide performance. Adding a surfactant or penetration oil did not change the volume median diameter or proportion of spray liquid in droplets < 150 μm. Less drift was found when using two-chamber cone nozzles at 3 bar than with flat-fan spray nozzles at 1.5 bar. It is concluded that the two-chamber cone nozzle is useful for fungicide application when drift must be avoided.     

Role of EphA4 and EphrinB3 in local neuronal circuits that control walking

Local circuits in the spinal cord that generate locomotion are termed central pattern generators (CPGs). These provide coordinated bilateral control over the normal limb alternation that underlies walking. The molecules that organize the mammalian CPG are unknown. Isolated spinal cords from mice lacking either the EphA4 receptor or its ligand ephrinB3 have lost left-right limb alternation and instead exhibit synchrony. We identified EphA4-positive neurons as an excitatory component of the locomotor CPG. Our study shows that dramatic locomotor changes can occur as a consequence of local genetic rewiring and identifies genes required for the development of normal locomotor behavior.     

DNA markers provide insight about common lime in historical plantings – An example from the Royal Danish Gardens

As part of the restoration process of an avenue of common lime (Tilia × europaea) from 1760 in the Royal Danish Gardens, all remaining trees were genotyped with DNA markers before they were felled. As such, information about the nature of the plant material (clonal versus non-clonal) and mode of propagation was obtained, revealing that a single clone constituted 92% of the remaining trees (106 out of 115). Five trees were of another clone, while the remaining four trees had unique genotypes. Mode of clonal propagation was most likely layering since the genotype of the crown and the roots of a subsample of the trees had the same genotype. Trees from four other locations with historical avenues/plantings from the 17th century were also genotyped. The two clones registered in the first location were also found at the other four locations. Of 76 trees from the other historical avenues/plantings, only two trees did not belong to either of the two clones. Genotyping of commercial common lime trees that would be planted in place of the felled trees during the restoration project was also performed. Samples of 20 newly planted trees all possessed the same genotype as the majority of the old felled trees and, thereby, were the same clone as the trees planted nearly 250 years ago. Altogether, the current study shows that the genetic diversity of common lime planted in Danish historical plantings is extremely narrow, and that the same clones have been produced for decades/centuries by private nurseries in the Netherlands and Germany. It also provides evidence that it is possible to obtain the same genetic material as originally planted when common lime trees are to be replaced in historical plantings. Furthermore, the utility of DNA markers in the management of plant material in parks is demonstrated.