Date of Award

2005

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Animal Sciences

Advisor

James Weber

Second Committee Member

Kenneth Andries

Third Committee Member

Robert Causey

Abstract

Gastrointestinal nematode infection in sheep is currently considered to be a problem of great magnitude in sheep production worldwide. This problem has been compounded by the overuse of anthelmintics used to treat parasite infection. In efforts to reduce chemical dependant production, research has focused on selection for parasite resistance based on worm load. Due to the low heritability of this trait any change effected by selection would take many years to realize. Selection for resistance can be improved by using more specific traits acted upon by fewer genes. Markers that are linked to the immune response to a parasite infection are great candidate genes to evaluate use in a genetic marker selection program. For the past five years, the Northeast Katahdin Hair Sheep Project has been C breeding Katahdins for improved parasite resistance. Lambs from the hair sheep project were used in this study, all of which were 3/4 Katahdin (n=28). To evaluate resistance, lambs were naturally and artificially infected with the nematode Haemonchus contortus in a process called priming. Data from the initial artificial infection were used to determine levels of resistance based upon fecal egg count (FEC) and packed cell volume (PCV). Lambs under artificial infection showed a weak infection and there was no difference in FEC or PCV between the lambs (p > 0.05) and were all considered to be resistant. Lambs were treated with levamisole (8mgIkg) and held kept free of parasite infection for fourteen days post anthelmintic treatment. Lambs were then divided into control and treatment groups, where they received an oral dose of PBS or 10,000 L3 Haemonchus contortus larvae, respectively. Lambs were tested weekly post infection for 6 weeks. On the third week p.i. the lambs showed symptoms of parasite infection. Fecal egg count peaked on 28d p.i. at 4,168 epg and began to recede each following week to the end of the study where the mean FEC was 3,021 epg. The control lambs, grown in the same location, did not become infected. Resistance was determined on the mean fecal egg count, packed cell volume and FAMACHA anemia scores and lambs were grouped into low and high resistance groups. The low resistance group differed from the high group in FEC, PCV, and FAMACHA (p C0.05). There was no difference found in the DNA sequences of the 27 lambs tested as they all had the same allele of CSRD 2138. It is unlikely that a different allele exists in the local population as it is inherited codominantly. This candidate marker needs more research with breeds susceptible to Haemonchus contortus. The response from the lambs in this study shows that breeding for resistance can be improved faster by crossbreeding with breeds that show more parasite resistance.

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