Published Research on PARASITE RESISTANCE of St. Croix Sheep (with Links to site-of-origin)
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1: Vet Parasitol. 1992 Mar;41(3-4):211-25. Related Articles, Links

Resistance of St. Croix lambs to Haemonchus contortus in experimentally and naturally acquired infections.

Gamble HR, Zajac AM.

U.S. Department of Agriculture, Agricultural Research Service, Helminthic Diseases Laboratory, Beltsville, MD 20705.

Parasitological and immunological parameters of experimental or naturally acquired infections with Haemonchus contortus were compared in St. Croix and Dorset lambs. In experimental infections, St. Croix lambs developed significantly greater levels of resistance to H. contortus, following primary exposure, as compared with Dorset lambs. This resistance was influenced both by age and by prior exposure to parasites. In grazing experiments on H. contortus-infected pasture, St. Croix lambs shed significantly fewer eggs as early as 5 weeks following initial exposure. Further, St. Croix lambs had more than 99% fewer worms in the abomasum at necropsy compared with age-matched Dorset lambs. Lymphoproliferative assays using peripheral blood mononuclear cells and antigen-specific serological tests demonstrated only minor differences in immune responsiveness between the two breeds despite the dramatic parasitological differences. Similarly, abomasal mucus from both breeds had elevated levels of parasite-specific antibodies and contained substances mediating larval paralysis. In contrast, St. Croix lambs which had become resistant to nematode infection had dramatically higher numbers of globule leukocytes in the abomasal mucosa compared with Dorset lambs.

PMID: 1502784 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1502784&dopt=Abstract

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Title: Resistance to Gastrointestinal Parasites in Dorper, Katahdin, and St. Croix Lambs in the Southeastern United States

Authors

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Burke, Joan

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Miller, J - LOUISIANA STATE UNIV

Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 9, 2003
Publication Date: August 1, 2004
Citation: Burke, J.M., Miller, J.E. 2004. Resistance to Gastrointestinal Parasites in Dorper, Katahdin, and St. Croix Lambs in the Southeastern United States. Small Ruminant Research. 54:43-51.

Interpretive Summary: Current anthelmintics available to sheep producers, as well as some approved for other species, have become ineffective for controlling internal parasites. Lambs are very susceptible to internal parasites. Some hair sheep ( St. Croix) possess a greater resistance to these parasites compared with wool breeds. Resistance of Dorper and Katahdin lambs is unknown. Therefore, parasite resistance among hair and wool breed lambs was examined and found to be similar among hair breeds when the parasite challenge was relatively low. Dorper lambs tolerated the infection more so than Suffolk (wool) lambs when fecal egg counts were low. However, as the challenge escalated, parasite resistance was greatest in St. Croix lambs, followed by Katahdin and Dorper lambs. This information is important to producers and extension agents with an interest in hair sheep.

Technical Abstract: A study was conducted to evaluate resistance to a natural or induced gastrointestinal (GI) nematode infection in hair and wool breeds of lambs. Experiment 1 evaluated parasite resistance of fall born Dorper crossbred (DO; n = 17) or St. Croix (SC; n = 17) lambs. Ewe and wether lambs were weaned at 84 ± 1.1 days of age and dewormed. Fecal egg counts (FEC) and blood packed cell volume (PCV) were determined between weaning and 56 d later. In Experiment 2, natural GI nematode infection was evaluated among spring born DO (7/8 or 3/4 Dorper; n = 24), Katahdin (KA; n = 26), SC (n = 8), and Suffolk (SU; n = 10; wethers only) ewe and wether lambs from weaning (60 ± 1.3 d of age; April) to 172 ± 1.3 d of age (August). Lambs were dewormed if the breed average FEC was 1000 eggs/g. Treatment for all breeds occurred in early and late June. In both studies, lambs grazed bermudagrass overseeded with ryegrass, previously grazed with sheep, and were supplemented with 225 to 500 g of corn/soybean meal supplement. Experiment 3 examined resistance of DO (n = 8), KA (n = 8), and SC (n = 9) ewe lambs to induced GI infection (20,000 L3 stage Haemonchus contortus). Lambs were weaned at 62 ± 2.3 d of age, dewormed 22 d later and inoculated 6 d later (Day 0). In Experiment 1, FEC was greater (breed x time, P<0.09) at weaning in DO lambs and PCV was similar between DO and SC lambs. In Experiment 2, FEC was greatest and PCV least in DO lambs when compared with other breeds. After deworming, PCV was lowest in SU lambs (breed x time, P<0.001). In Experiment 3, on Day 28, FEC was greater (P<0.05) in DO and KA lambs compared with SC lambs. By Day 42, 4 DO, 6 KA, and 3 SC lambs had been dewormed. With a moderate biological challenge, parasite resistance was similar among the three hair breeds examined and greater in hair than wool breed lambs. When the challenge escalated, St. Croix lambs were most resistant and Dorper crossbred lambs were similar or less resistant than Katahdin lambs.

   

 

 

http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=134476

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St. Croix Sheep vs. Parasites

Trichostrongyles or gastrointestinal parasites are one of the most common and costly constraints in sheep production worldwide. The resulting disease can require treatment with anthelmintics, or is often deadly. Adult sheep are able to develop an immunity with repeated exposure. Lambs, however, are highly susceptible to the parasites. They can become anemic and die without treatment. The St. Croix, a tropical breed of haired sheep, shows a remarkable genetic resistance to the parasites. Although considered a poor producer, the St. Croix can survive on sparse forage with minimal management.

Grazing trials were conducted on contaminated pastures by scientists at the Agricultural Research Service in Beltsville, Maryland. St. Croix lambs developed an almost complete resistance to the parasite after four to six weeks of exposure. Dorset lambs, a common wool breed, were grazed under the same conditions and required treatment for parasite infection. The St. Croix had over 99% fewer worms in the abomasum (fourth stomach) than the Dorset, and passed only 0.5% as many parasite eggs in the feces.

The resistance is accompanied by a high number of certain immune cells called globule leucocytes, in the abomasum of the St. Croix. Although the exact method is not known, these cells might function to prevent the parasite from attacking the stomach lining, or expel the parasites from the abomasum.

When the St. Croix are crossbred with sheep of a lesser tolerance to parasites, offspring lose most of the genetic resistance. Understanding the immune process could lead to the transfer of resistance through breeding or vaccination. This can potentially benefit the ovine industry, where losses due to stomach parasites total $300 million annually. Additional research is needed.

Mazzola, V. 1990. St. Croix sheep resist worms. Agricultural Research: Oct. 1990. p.27.

Gamble, H.R. 1991. Resistance to Internal Parasites in Tropical Breeds of Sheep.

For more information:

H. Ray Gamble
Helminthic Diseases
Laboratory USDA-ARS, BARC East
Beltsville, MD 20705 USA

http://www.fadr.msu.ru/rodale/agsieve/txt/vol3/6/a8.html