| Anthelmintic resistance of gastro-intestinal nematodes of small ruminant(sheep and goat)is a severe problem throuhout the world, which has not yet been concerned in China. With the need for our sheep and goat production and for control of parasites, the study was carried out in the following aspects. The results were as follows:(1)A survey was conducted by the faecal egg count reduction test(FECRT)on 18 farms(12 sheep ones and 6 goat ones)in Ningxia Autonomous Region of west-northern China. Resistance to albendazole was detected on 25% (4/16) of farms, and resistance to avermectin (AVM ) was considered as suspected on two out of six farms.(2)On 25 samples from 23 farms in Ningxia and Inner Mongolia Autonomous Region,LD50 values(anthelmintic concentration producing 50% inhibition of hatching) for albendazole and thiabendazole respectively were compared in vitro egg hatch assay (EHA). The results showed that the LD50 values for both were of no significant difference. In addition, the results were above 75% agreement in the detection of benzimidazole(BZ)between the FECRT and the EHA.(3)A vitro selection experiment was carried out for a suspected-resistant worm population from the field. With this isolate as a control one, A larval development assay (LDA)was used as screening method to detect BZ, Levamisole(LEV)and AVM.(4)A field isolate of Haemonchus contortus(H. contortus)was iditified as susceptible to AVM and LEV, and as resistant to BZ(resistance facter:10). After lambs were infected with the resistance isolate, faecal samples were collected from 22 to 72 days. The LD50 values in EHA increased to a peak about 50 days later and then declined gradually.(5)The polymorphism in partial fragment of the beta-tubulin gene was examined in H. contortus from treated and untreated populations using single-strand confirmation polymorphism(SSCP)analysis. The results of analysing 181 male adults revealed 20%(3/15)mutant individuals, 60%(9/15)heterozygous ones and 20%(3/15)normal ones in the treated populations, and 3.6%(6/166), 7.8%(13/166)and 88.6%(147/166)respectively in the natural infectious populations.(6)A restriction fragment length polymorphism-poly merase chain reaction (RFLP-PCR)technique was developed for detection of the mutation at 200 codon of the beta-tubulin isotypeâ… gene for 64 H. contortus individuals from the field, including 10 adults treated with BZ. Results showed that frequency of BZ-resistance alleles was 45% in the treated populations, and averagely 9.3% in the other natural infectious populations.(7)A 370bp fragment of the beta-tubulin isotypeâ… gene of H. contortus has been sequenced from several populations in 4 different regions. Comparing with the sequence corresponding to beta-tubulin gene of published BZ-resistance isolate indicated that there were 12 polymorphic sites in the amplified fragments, and the Diversity of genetic and BZ-resistance alleles were existed in population of H. contortus .(8)The states of parasite nematode infection in three types of feeding pattern was investigated from 90 samples on 6 farms in the West-north of China. In the condition of zero-grazing, contrasting to grazing, gastro-intestinal nematodes infection decreased relatively, and in half-grazing, it was between the zero grazing and grazing condition. In the same feeding condition, infection rate and intensity of nematodes in goats were higher than in sheep. Finally, the author suggested that current parasite control required integrated management strategy.
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