日粮抗氧化剂减少肉鸡的腹水症

低死亡率和较高的饲料利用率 ,看来是鸡抗氧化状态得到改善的结果。增高日粮维生素E的含量并应用有机硒可减少肺高压 (腹水症 )引起的死亡。     

Antimicrobial substances and chick growth promotion: The growth‐promoting activities of antimicrobial substances,including fifty‐two used either in therapy or as dietary additives

1. Fifty‐five antimicrobial substances were tested for their ability to promote growth when added to the diet of chicks.

2. Both cephalosporins and all the nine penicillins tested were active.

3. Of six aminoglycosides, streptomycin and gentamicin had the greatest activity and neomycin had none.

4. Growth rate was significantly improved by clindamycin, lincomycin, vancomycin, spectinomycin, rifampicin, oxytetracycline, chlortetracycline, erythromycin, tylosin, flavomycin, virginiamycin and zinc bacitracin. Chloramphenicol and nalidixic acid were inactive. Polymixin B, novo‐biocin, cycloserine, phosphonomycin, and sodium fusidate had little activity. Fusidic acid promoted growth at 250 mg/kg diet.

5. Trimethoprim was inactive alone and in combination with sulpha‐diazine. Of seven 5‐nitroimidazoles, only dimetridazole and metronidazole showed slight activity. Of the six 5‐nitrofurans, only nitrovin, the standard reference substance used, promoted growth.

6. Caprylohydroxamic acid, a urease inhibitor, had no beneficial effect on growth rate or on the efficiency of food conversion.

7. The growth‐promoting properties of the various substances could not be related with their known antimicrobial and absorption characteristics in mammals.     

Detection of genes with moderate effects on disease resistance using ovine mhc and resistance to nematodes as an example

Detecting some of the genes that influence disease resistance would improve our understanding of the processes that cause disease and also simplify disease control. Genes within the major histocompatibility complex (mhc) are strong candidates for disease resistance and they have been intensely studied for the last 30 years. Recently, several groups working independently have reported the existence of alleles within the mhc that are associated with enhanced resistance to nematode infection. This article uses hindsight to describe some of the potential pitfalls that hinder the search for valid disease resistance genes. The search requires a good understanding of disease biology, molecular genetics, statistical genetics and especially, the design and analysis of experiments. The power to detect mhc effects is quite low and is quite sensitive to the frequency of the putative resistance alleles.     

Rht1(B. dw), an alternative allelic variant for breeding semi-dwarf wheat varieties

The vast majority of the world's acreage of semi-dwarf wheat varieties is at present cultivated with varieties carrying one of two genetically similar dwarfing genes, Rht1 and Rht2, derived from the Japanese variety ‘Norin 10’. Near-isogenic lines have been developed and tested to determine the breeding potential of an allelic variant of Rht1, designated Rht1(B. dw). Following its introduction into four varietal backgrounds, Rht1 (B. dw) was seen to reduce height by around 25%, to increase the number of grains setting in spikelets and ears by around 20%, to reduce grain weight by 10%, and to increase yields of plants grown under spaced or drilled conditions by about 8%. When compared to the commercially utilized Rht1 allele, as near isogenic lines in a ‘Mercia’ varietal background, Rht1 (B. dw) gives a significantly greater reduction in plant height, a greater increase in spikelet and ear fertilities, slightly less reduction in 1000-grain weight, and significantly higher spikelet, ear and plot yields. If these results are repeatable in other varietal backgrounds, over seasons, and under differing environmental conditions, Rht1 (B. dw) should have considerable commercial potential as an alternative allele for producing shorter-than-average, high-yielding, semi-dwarf wheat varieties.     

Allelic variation at the dwarfing gene Rht8 locus and its significance in international breeding programmes

A microsatellite marker WMS261 developed at I.P.K., Gatersleben,Germany, co-segregates with the semi-dwarfing gene Rht8. Screens ofover 800 wheat varieties from 20 countries show 90% carry WMS-261alleles with 165, 174 or 192 base pairs (bp). The 192bp allele diagnosticof Rht8 occurs in most screened Southern European varieties. Anallele with 165 bp occurs in the majority of CIMMYT Mexican varieties andin most varieties bred in countries that utilize CIMMYT germplasm.Agronomic studies of single chromosome recombinant line mappingpopulations segregating for WMS 261 alleles with 165, 174 or 192 bp,show compared to the 174bp allele the 192bp allele reduces height byaround 8 cm and the 165 bp allele increases height by around 3cm. Theresults indicate the importance and widespread utilization of Rht8 asa dwarfing gene in southern Europe and suggest an adaptative significanceto the height promoting 165 bp allele in CIMMYT material.     

Bovine spongiform encephalopathy: aspects of the clinical picture and analyses of possible changes 1986-1990.

A standard questionnaire was used to record the presence of specific clinical signs reported for histopathologically confirmed cases of bovine spongiform encephalopathy observed before June 30, 1990, and the frequencies of these signs were analysed. The signs most frequently recorded were apprehension, hyperaesthesia and ataxia, and there were variations in the frequency with which some signs were recorded in animals observed at different times during the epidemic. These variations were considered to be the result of differences between observers and differences in the duration of the illness, rather than a change in the clinical picture, which could possibly have occurred with a change in the nature of the agent to which the cattle had been exposed, or to a change in their response to the agent.     

Maasai herd and flock structures in relation to livestock wealth,climate and development

Information was obtained on the structure of the herds and flocks of a sample of 41 households on the three Maasai Group Ranches in Kenya. The purpose of the survey was to contribute to an intensive study of the livestock production system, and also to assess the amount of information that could be obtained from a herd structure study on its own. Differences in herd structure were related to the livestock wealth of the household, the stage of development of the Group Ranch as well as to the variation in climate, and production alternatives.Data from more than 5100 cattle revealed that Maasai herds contained less steers in 1982 (18%) than in 1968 (22%). The proportion of mature steers had also dropped from 5% (1968) to 2% (1982), with maximum valves of 3·2% on the most developed ranch and 2% for the wealthiest stratum of households. A high percentage of females had been retained (56%) giving a herd structure characteristic of subsistence production with milk as a primary output. This structure also caters for a strong market in immature animals and gives the herd a high potential for recovery after a drought. There appeared to be a trend towards increased use of introduced bulls, notably Sahiwal on the Small East African Zebu, with increased Group Ranch Development. However, this trend was confounded by a decreasing aridity gradient with increased development.On two of the ranches for which 1968 counts were available, cattle numbers were 119% of their previous value whereas small stock were 470%. The reason appears to be that increased sedentarisation without adequate range management has resulted in a severe reduction in grasses, and their replacement by forbs. These plants are more palatable to small stock which are better able to exploit the degraded habitat.Information from more than 2730 sheep and 2300 goats revealed that poor households preferred goats and richer households, sheep. The Small East African Goat was ubiquitous, but the most developed ranch had crossed Dorper onto Maasai sheep whereas the least developed and most arid ranch had introduced Somali Blackhead sheep. The Dorper crossbred catered for a market for mutton whereas the Blackhead was primarily for home consumption of fat.The conclusion is that Group Ranch Development has not projected the Maasai into commercial beef ranching as originally planned, but their production system has not stood still. A study of herd structures was a good way of demonstrating the evolution of the system. The method was simple but was dependent for its success on fairly involved and time-consuming sampling and data collection procedures.     

Gastrointestinal nematode infection in sheep--a review of the alternatives to anthelmintics in parasite control

Efforts to curb production losses caused by nematode parasitism in sheep have led to the development of a number of control methods to complement or replace anthelmintics. The need for alternative control measures stems from the emergence of anthelmintic-resistant parasitic nematodes with reports of multi-class resistance to these drugs now emerging. A number of these control methods such as predacious microfungi, protein supplementation, plant extracts in feed and vaccines have demonstrated potential to control infection but require development and examination under natural conditions. Breeding for natural resistance to nematode infection has already shown success in controlling the disease under natural conditions. Selection for resistance is currently based on fecal egg count measurements but identification of genetic indicators of resistance will provide a more efficient method of selection. Current quantitative trait loci for nematode resistance include the MHC genes, interferon gamma gene, IgE gene and microsatellites on chromosome 1, 5 and 6. This paper reviews the current alternatives to anthelmintics to control infection, with an emphasis on breeding for host resistance and identification of genetic indicators of resistance.     

A case study of capture-recapture methodology using scrapie surveillance data in Great Britain

We applied capture–recapture methodology (CRC) to data from three surveillance sources (statutory notification, abattoir survey (AS) and fallen stock (FS) survey) to estimate the number of holdings infected with scrapie in Great Britain and to assess the sensitivity of the surveillance network. Between January 1, 2002 and March 31, 2003, 144 holdings were identified by the three sources. Using CRC modelling techniques, we estimated a minimum lower bound for the total number of holdings infected as 642. A biologically plausible positive dependence between the statutory reporting and the fallen stock survey was found statistically significant. The sensitivity of the three sources combined was very low. The integration of the three overlapping sources provided a better understanding of the interactions within the surveillance network. However, the scarcity of the data and reduced overlapping among sources only allowed for very cautious inferences to be drawn about the true proportion of scrapie affected holdings in the national population. Future surveys and surveillance activities should be planned such that the resulting data can be used more effectively as part of CRC modelling approaches.