放牧家畜的践踏作用研究评述

放牧家畜的践踏作用是家畜作用于草地的 3个途径之一 ,相对于采食和排泄物的作用具有作用时间长、直接作用的草地组分多和效果持久的特点。家畜践踏损伤牧草、埋实种子、促进萌发 ,减少凋落物的现存量 ,增加土壤的紧实度、容重 ,降低土壤孔隙度、水稳性团聚体、透水性和透气性 ,导致雨后水涝和植物根区缺氧 ,引发水土流失。国内外使用的 4种践踏强度指标分别存在不确定性大、忽视践踏强度的时间依赖性和畜种间差异、没有考虑放牧行为及其时间分配模式等问题 ,分析认为践踏强度应为家畜放牧行为、不同行为的持续时间、家畜体重、放牧地面积和坡度的函数。家畜的践踏作用因草地的健康状况差异而与之存在正或负的反馈机制以及践踏强度阈值 ,可能在草地退化和健康维护中起主导作用。今后需建立严格的研究方法和科学的践踏强度指标 ,重视草地植被对践踏的耐受阈限、践踏对牧草更新的调控机理及其对凋落物产生和分解的影响 ,以及土壤水分与践踏作用的关系 ,确定放牧系统的践踏强度阈值。     

Occupational health problems among migrant and seasonal farm workers.

Migrant and seasonal farm workers are one of the most underserved and understudied populations in the United States. The total US population of such farm workers has been estimated at 5 million, of whom about 20% live or work in California. Farm workers perform strenuous tasks and are exposed to a wide variety of occupational risks and hazards. Low socioeconomic status and poor access to health care also contribute to existing health problems in this population. Potential farm work-related health problems include accidents, pesticide-related illnesses, musculoskeletal and soft-tissue disorders, dermatitis, noninfectious respiratory conditions, reproductive health problems, health problems of children of farm workers, climate-caused illnesses, communicable diseases, bladder and kidney disorders, and eye and ear problems. Few epidemiologic studies exist of these occupational health problems. No comprehensive epidemiologic studies have assessed the magnitude of occupational health problems among migrant and seasonal farm workers and their dependents. Although the migratory nature of this population makes long-term studies difficult, the development of standardized data collection instruments for health consequences and scientific assessment of farm work exposures and working conditions are vital to characterize and reduce the occupational health risks in farm workers.     

Method to estimate genotype probabilities at individual loci in farm livestock

Summary A Bayesian method to estimate genotype probabilities at a single locus using information on the individual and all its relatives and their mates has been developed. The method uses data over several generations, can deal with large numbers of individuals in large livestock families and allows for missing information. It can be extended to multiple alleles and can be used for autosomal or sex-linked loci. The allele frequencies and the form of expression (dominance, penetrance) must be specified. An algorithm using the method and involving an iterative procedure has been developed to calculate the genotype probabilities for practical use in livestock breeding. The method and algorithm were used to determine the accuracy of estimating genotype probabilities of sires for a female sex-limited trait, such as genetic variants of milk proteins. Data were similated and genotype probabilities estimated for 100 sires (20 replicates) with 3, 6 and 12 female offspring per sire, for different population frequencies, for additive and dominance gene action and for variable genotypic expression. Such simulation is useful in the design of testing systems for the use of information on specific genetic loci in selection.Prepared during a leave at Centre for Genetic Improvement of Livestock, Guelph, Canada     

Extremal problems for topological indices in combinatorial chemistry.

Topological indices of molecular graphs are related to several physicochemical characteristics; recently, the inverse problem for some of these indices has been studied, and it has some applications in the design of combinatorial libraries for drug discovery. It is thus very natural to study also extremal problems for these indices, i.e., finding graphs having minimal or maximal index. In this paper, these questions will be discussed for three different indices, namely the sigma-index, the c-index and the Z-index, with emphasis on the sigma-index.     

矿区废弃地土壤动物研究进展

土壤动物的侵入与定居是矿区废弃地群落结构形成的重要途径.随着矿区废弃地废弃时间的增加,土壤动物群落结构不断改变,这对于矿区废弃地生态系统演替与生态恢复具有重要的作用.本文综述了矿区废弃地土壤动物生态环境、土壤动物迁居与群落演替、土壤动物活动对土壤过程的影响、土壤动物对矿区废弃地环境的响应及其指示意义等方面的研究进展.在对已有成果进行综合分析的基础上,就目前矿区废弃地土壤动物研究中亟待解决的一些问题进行了探讨,并提出今后应加强研究的方向.     

Analyses of livestock production, waste storage, and pathogen levels and prevalences in farm manures

Survey results describing the levels and prevalences of zoonotic agents in 1,549 livestock waste samples were analyzed for significance with livestock husbandry and farm waste management practices. Statistical analyses of survey data showed that livestock groups containing calves of <3 months of age, piglets, or lambs had higher prevalences and levels of Campylobacter spp. and Escherichia coli O157 in their wastes. Younger calves that were still receiving milk, however, had significantly lower levels and prevalence of E. coli O157. Furthermore, when wastes contained any form of bedding, they had lowered prevalences and levels of both pathogenic Listeria spp. and Campylobacter spp. Livestock wastes generated by stock consuming a diet composed principally of grass were less likely to harbor E. coli O157 or Salmonella spp. Stocking density did not appear to influence either the levels or prevalences of bacterial pathogens. Significant seasonal differences in prevalences were detected in cattle wastes; Listeria spp. were more likely to be isolated in March to June, and E. coli O157 was more likely to be found in May and June. Factors such as livestock diet and age also had significant influence on the levels and prevalences of some zoonotic agents in livestock wastes. A number of the correlations identified could be used as the basis of a best-practice disposal document for farmers, thereby lowering the microbiological risks associated with applying manures of contaminated livestock to land.     

The inverse problems for some topological indices in combinatorial chemistry.

In the original paper, Goldman et al. (2000) launched the study of the inverse problems in combinatorial chemistry, which is closely related to the design of combinatorial libraries for drug discovery. Following their ideas, we investigate four other topological indices, i.e., the sigma-index, the c-index, the Z-index, and the M(1)-index, with a special emphasis on the sigma-index. Like the Wiener index, these four indices are very popular in combinatorial chemistry and reflect many chemical and physical properties. We give algorithmic and analytical solutions for the inverse problems of the four indices. We also show that the SUBTREEVALUE reconstruction problem for the sigma-index is NP-hard.     

Bioinorganic chemistry of open-angle glaucoma: A review

At present, physical methods of chemical analysis are constantly improving providing large amount of data on elemental composition of organs and tissues. However, only few works describe the correlation (or the potential connection) between the general or local bioelemental imbalances and specific biochemical reactions that are involved in pathogenesis of certain diseases. This review describes primary open-angle glaucoma (POAG) – one of the most common ophthalmic diseases – in terms of elemental chemistry. The authors look into the impact that various subgroups of elements have on passive and active processes of homeostasis regulation and hydrodynamic balance in the eye. Alkaline metals and their analogues (K, Na, Li, Rb, Cs) influence hydrostatics and hydrodynamics by means of both K-Na pumps and osmosis. Alkaline-earth elements and their analogues (Ca, Mg, Sr, Ba, Be) are involved in biomineralization and intercellular interaction in the drainage areas. Chalcophile metals and their analogues (Zn, Cu, Hg, Co, Ni, Cd, Pb, Mo, Sb) regulate redox reactions. They are the cofactors of enzymes that support structural homeostasis of the drainage area. Siderophile metals (Fe, Mn, Cr, Rh) regulate oxidation-reduction reactions, including those associated with limited nutrition of tissues in glaucoma. The role of amphoteric metals and nonmetals (Al, Si, Ga, V, TI, Sn, Ge, Zr, W) in POAG has not been described properly, but they were noted to participate in mineralization. Structure-forming non-metals and their analogues (N, S, Se, As) are directly involved in the formation of protein and non-protein aggregates that prevent aqueous humor outflow. The specific role of phosphorus in the pathogenesis of glaucoma has not been described previously. The authors analyze the involvement of phosphorus in energy-dependent processes of cellular activity, which are aimed at the reprocessing of aggregates that cause aqueous humor retention.     

Immunity to adult cestodes: basic knowledge and vaccination problems. A review.

Immunity in mammals to intestinal cestodes has been reviewed using the normal final host infected with the tapeworms Hymenolepis diminuta in rats and H. microstoma and H. nana in mice as a model. Primary infections up to a certain level continue to live as long the host, while most worms in infections with larger doses are destrobilated and expelled. It has been argued that concomitant immunity against a superimposed infection exists in rats and mice infected with H. diminuta and H. microstoma, respectively, and suggested that it also takes place in humans infected with Taenia spp. Immunity to secondary infections after expulsion of a primary infection occurs, but immunological memory is rather short-lived, although depression of worm growth occurs for at least two third of the rat's life. Serum antibodies have been shown to produce a direct precipitate on the surface of cestodes in vitro, but a direct effect of antibodies in vivo or the relationship with e.g. host effector cells, like mast cells and eosinophils, is unknown. It has been shown that peritoneal exudate cells from rats are able to kill H. diminuta in vitro. Very little is known about the mechanisms of tapeworms to counteract host immunological responses, but the tegumental glycoconjugates and discoidal secretory bodies are possible candidates. Passive transfer of immunity by mesenteric lymph node cells has only been successful using cells from H. nana egg-infected mice and has shown that only short-lived proliferating cells are responsible for transferring immunity. Vaccination procedures and problems are discussed with special reference to E. granulosus in dogs.     

Seasonal and physiological variations in serum chemistry and mineral concentrations in cattle

The present study reports the seasonal and physiological variations of copper, zinc, magnesium, iron sodium chlorine, potassium, calcium, phosphorus, urea, alkaline phosphatase (ALP), creatinine (CR), aspartate aminotransfrase (AST), alanine aminotransferase (ALT), cholesterol, albumin, globulin, lactate dehydrogenase (LDH), and total protein concentrations in cattle. Two groups of mated (n=14) and nonmated (n=10), healthy cows were selected for the study. Serum samples were collected at each of four periods: (1) early pregnancy (May), (2) midpregnancy (August), (3) late pregnancy (October), and (4) lactation (February). Physiological variations result in changes of cholesterol, calcium, LDH, and total protein concentrations. Phosphorus varies only with seasonal but not physiological changes, whereas ALP, copper, magnesium, and potassium concentrations change with physiological and seasonal conditions. The copper concentration is increased through the pregnancy. Neither the seasonal nor the physiologic variations affect zinc, iron, sodium, chlorine, calcium, urea, creatinine, albumin, and globulin values in both groups in all periods. Thus, these values can be used as reference for both mater and nonmated bovines. The measured total protein might not reflect its true value because of dehydration during the hot season. These observations suggest that seasonal and physiologic variations have to be taken into consideration for the correct interpretation of serum chemistry and elements status in cattle. Nutritional supplements are required for cattle during certain periods to avoid a decline of their performance, which would then represent consequent economic loses.     

The chemical control of livestock parasites: problems and alternatives

Over 200 classes of chemical compounds are currently in use for the treatment of livestock parasites. Here Les Strong and Richard Wall review some of the problems arising from the total reliance on chemical control and consider some of the alternative methods that might be given more thought and application.     

The biology and chemistry of antifungal agents: A review

In recent years their has been an increased use of antifungal agents and has resulted in the development of resistance to drugs. Currently, use of standard antifungal therapies can be limited because of toxicity, low efficacy rates. Different types of mechanisms contribute to the development of resistance to antifungals. This has given raise to search for a new heterocycle with distinct action or multitargeted combination therapy. This review addresses the areas such as the underlying mechanisms, eight different targets such as ergosterol synthesis, chitin synthesis, ergosterol disruptors, glucan synthesis, squalene epoxidase, nucleic acid synthesis, protein synthesis, microtubules synthesis. The clinically employed drugs along with the current research work going on worldwide on different heterocycles are discussed. In recent advances various heterocycles including imidazole, benzimidazole etc., twenty three scaffolds and their lead identification are discussed.     

Detecting autocorrelation problems from GPS collar data in livestock studies

Uneven use of grasslands and savannas by livestock has a significant impact on ecosystem productivity, biodiversity, and function. In studies of livestock distribution, global positioning systems (GPS) collars are frequently used and the rapid rate of technological improvement has brought new opportunities to collect extremely large amounts of very accurate spatial information. However, these advances also pose statistical challenges associated with the analysis of large, temporally correlated, datasets. Our main goal was to find the optimal sampling time intervals for GPS collar schedules when studying livestock distribution in semi-arid ecosystems. The schedule must provide maximum spatio-temporal information while avoiding problems of autocorrelation of sequential locations to provide a methodology that is both practical and statistically valid. We used GPS collar data collected in the Southwestern region of the United States. In each study cattle were tracked and data were recorded every 5 min. Location information from the 5-min GPS fixes were subsampled into 10, 20, 30, 60, 90, 120, 150, 180, 240, 300, 360, and 420-min regular intervals. We calculated the Euclidean distance between pairs of successive locations then conducted correlation analyses to determine the degree of similarity between successive traveled distances. We then selected two correlated and two non-correlated time-interval datasets to compare estimates of kernel home range and minimum convex polygon areas. Successive Euclidean distances between GPS locations were significantly correlated when time intervals were <120 min. The calculated distance traveled was significantly reduced as time intervals between successive locations increased. Kernel home range values were smaller in correlated than in non-correlated datasets yet minimum convex polygon values were greater in correlated data than in non-correlated data sets. Our study shows the importance of considering different livestock sampling time intervals using GPS to achieve accurate and meaningful results on animal distributions especially in semi-arid ecosystems. Circumstances in which researchers may elect to use short-time interval autocorrelated data sets are also discussed.     

养殖环境中抗生素抗性基因的研究进展

抗性基因在环境中的垂直及水平传播,致使抗生素耐药性成为危及人类和动物生命健康的全球性问题。动物源食品是中国美食不可或缺之物,而由于抗生素超用与滥用等行为让公众不得不关注动物源食品源头——养殖场的抗生素抗性基因环境安全问题。本文综述了养殖环境中抗生素抗性基因的研究进展,分析了养殖环境中抗生素抗性基因产生原因、传播途径以及影响因素,介绍了现有风险评估方法和控制技术,并对今后养殖环境中抗生素抗性基因的控制策略、技术及研究方向提出了建议。     

Identifying and monitoring pain in farm animals: a review

One important objective for animal welfare is to maintain animals free from pain, injury or disease. Therefore, detecting and evaluating the intensity of animal pain is crucial. As animals cannot directly communicate their feelings, it is necessary to identify sensitive and specific indicators that can be easily used. The aim of the present paper is to review relevant indicators to assess pain in several farm species. The term pain is used for mammals, birds and fish, even though the abilities of the various species to experience the emotional component of pain may be different. Numerous behavioural changes are associated with pain and many of them could be used on farms to assess the degree of pain being experienced by an animal. Pain, as a stressor, is associated with variations in the hypothalamic–pituitary–adrenal axis as well as in the sympathetic and immune systems that can be used to identify the presence of pain rapidly after it started. However, most of these measures need sophisticated equipment for their assessment. Therefore, they are mainly adapted to experimental situations. Injuries and other lesional indicators give information on the sources of pain and are convenient to use in all types of situations. Histopathological analyses can identify sources of pain in experimental studies. When pronounced and/or long lasting, the pain-induced behavioural and physiological changes can decrease production performance. Some indicators are very specific and sensitive to pain, whereas others are more generally related to stressful situations. The latter can be used to indicate that animals are suffering from something, which may be pain. Overall, this literature review shows that several indicators exist to assess pain in mammals, a few in birds and very few in fish. Even if in some cases, a single indicator, usually a behavioural indicator, may be sufficient to detect pain, combining various types of indicators increases sensitivity and specificity of pain assessment. Research is needed to build and validate new indicators and to develop systems of pain assessment adapted to each type of situation and each species.     

Aspects of the chemistry and toxicology of indole-diterpenoid mycotoxins involved in tremorganic disorder of livestock

A method for the large-scale extraction ofNeotyphodium lolii (formerlyAcremonium lolii) infectedLolium perenne (perennial ryegrass) seed was optimized so as to efficiently obtain lolitrem B, the tremorgenic indole-diterpenoid compound thought to be the principal causative agent of the neurotoxic disorder ryegrass staggers. In a period of two weeks, 30 kg of seed could be processed yielding 125mg of pure, crystalline lolitrem B. In addition to lolitrem B, fifteen lolitrem analogues were isolated from the seed extracts and their structures determined by mass spectrometry and one- and two-dimensional NMR techniques. All but one of these analogues were previously unknown. Furthermore, three compounds related to paxilline, thought to be a precursor of lolitrem B were isolated fromPenicillium paxilli cultures. The isolation of the lolitrem and paxilline analogues provided much information on the likely pathways of lolitrem biosynthesis, and a detailed pathway is proposed. Paspaline was identified as the crucial intermediate in indole-diterpenoid biosynthesis, rather than paxilline, as previously thought. It is proposed that new endophyte incapable of biosynthesizing this substance will not produce any indole-diterpenoid tremorgens. Many of the lolitrem and paxilline derivatives isolated in the course of this study were tested for tremorgenic action in mice. These studies have identified a number of strucural features which are necessary for tremorgenic effect. Slow onset and long-duration tremors are characteristic of lolitrem compounds. For this effect, the acetal-linked isoprene unit and the stereochemistry at the A/B ring junction were identified as important. In contrast, paxilline compounds induce fast-onset and short-duration tremors. For this effect a C-13 α-orientated hydroxyl group is essential and the C-10 functionality is important. The extensive study of structure-activity relationships described in this thesis also suggests that lolitrem and paxilline compounds may exert their effects by binding to different target sites. Others have proposed that the more readily available paxilline be used as a model for the lolitrems in trials to select for animals resistant to ryegrass staggers, but the above observations suggest, however, that such an approach would not be successful.