ALABAMA A&M AND AUBURN UNIVERSITIES The Use of Breeds UNP-0006 Resistant to Internal Parasites

Gastrointestinal are commonly used; Parasite Life Cycle is a major problem in sheep however internal The life cycle of internal para- production worldwide. A parasites are becoming sites in sheep begins when monetary value for losses increasingly more the sheep eats the infective from parasites is difficult resistant to dewormers. larvae on a blade of grass. to ascertain, but it can In addition, there is Adult parasites stay in the be very substantial. This increasing awareness of abomasum (true stomach) publication presents an environmental issues that and lay tremendous num- approach that can be may influence the use bers of eggs. Haemonchus used in combination with of dewormers as more contortus requires 14 days strategic deworming and consumers demand to complete this part of the good pasture management products and pastures life cycle, while it normally to control internal parasites that are free of chemical takes Ostertagia circumcincta in sheep. This approach residues. Many consumers and Trichostrongylus spp. 21 involves breeding sheep are now questioning the days after the infective larvae for improved resistance to widespread use of chemicals are eaten for the adult to these parasites. in animal production mature and start to produce because of fears of human eggs. The eggs exit the host food contamination. For in the manure. The eggs then these reasons, alternative hatch into larvae, and the approaches for controlling infective larvae move from internal parasites are the manure onto the grass. being considered. Thus Conditions must be moist and far, a vaccination against warm in order for the eggs gastrointestinal parasites to hatch and move. Figure 2 in has not been shows the life cycle of gastro- found despite extensive intestinal parasites in sheep. Figure 1. Haemonchus contortus is the research. gastrointestinal parasite of sheep that causes the most harm. Photo from It is unlikely that future flickr.com. methods of parasite control in the sheep Loss of production, costs industry will rely on any of dewormers, andARCHIVE animal single approach but will death are some of the major probably be combinations concerns associated with of several approaches. the widespread occurrence To some extent, this is of with internal already happening with the parasites, particularly combination of strategic Haemonchus contortus deworming and good (Figure 1). Chemical pasture management. Figure 2. Life cycle of gastrointestinal dewormers, or parasite.

www.aces.edu Breeding for Improved Resistance Of the approaches to parasite control, breeding sheep for resistance seems to be the most promising application that can be used to complement the strategic use of dewormers and improved pasture Figure 3. Mature purebred Suffolk ram Figure 4. Mature purebred Florida Na- management. Resistance tive ram. Photo from wikimedia.org. refers to the sheep’s ability to suppress the establishment and/or development of parasites. From an economic point of view, resistance allows sheep to maintain existing levels of production even if they are infected. Australian researchers have termed this ability Figure 5. Mature purebred Suffolk ewes Figure 6. Mature purebred Florida Na- to maintain levels of tive ewe. Photo from wikimedia.org. production as “resilience.”

There is a substantial body The resistance values of Florida Native and Suffolk in this of evidence that supports trial suggest that parasitic resistance may be improved variation among breeds through systematic crossbreeding of these two breeds, and in resistance to internal other breeds may be able to be crossbred or backcrossed parasites, particularly to to the Florida Native to improve their resistance. Haemonchus contortus, Ostertagia circumcincta, Albers et al. (1987) concluded that breeding for resistance and Trichostrongylus to Haemonchus contortus may have positive effects on the spp. For example, the production capacity of Merinos. Large international sur- Gulf Coast, also known pluses of wool and meat as well as dwindling sheep market as Florida Native, is prices require reduction in production costs. Breeders who much more resistant to choose to reduce costs by breeding sheep with resistance Haemonchus contortus than to internal parasites are more likely to see cost savings are the European breeds than those who choose to increase the genetic potential for Rambouillet and Merino as more wool or meat. well as the Suffolk breed. In a trial conducted at Alabama There is a substantial body of evidence that supports the A&M University, Ruvuna and fact that some breeds are naturally more resistant to inter- ARCHIVEnal parasites in sheep than other breeds are. For example, Stephens (1997) observed that the egg per gram (EPG) Scrivner (1964) showed that Targhee is more resistant of feces was approximately than Rambouillet is. Table 1 summarizes this information. eight times lower in Florida Native ewes than in There is evidence that selection for resistance to inter- Suffolk ewes under natural nal parasites of sheep is feasible. Producers could reduce conditions of infection costs by breeding sheep such as the Florida Native or Flor- (Figures 3 through 6). ida Native crosses that are resistant to internal parasites

2 Alabama Cooperative Extension System Table 1.

Sheep Breed Comparisons for Resistance to Internal Parasites

Resistant Breed Comparison Breed Parasite Species* Reference Targhee Rambouillet Osp, Nsp Scrivner (1964) Scottish Blackface Finn Dorset Hc Altaif & Dargie (1978) Border Leicester x Merino Merino Osp Donald et al (1982) Florida Native Rambouillet Hc Jilck & Bradley (1969) Florida Native Dorset x Rambouillet Hc, Tsp Zajac et al. (1988) Florida Native Barbados Hc Courtney et al. (1985a) Florida Native Suffolk Hc Ruvuna & Stephens (1997) Red Maasai Merino Corriedale Hc Preston & Allonby (1978) Hampshire Red Maasai Dorper Hc Baker et al. (1994)

* Hc: Haemonchus contortus Osp: Ostertagia (Teladorsagia) species Tsp: Trichostrongylus species Nsp: Nematodirus species

(Figures 7 and 8). A pos- lambs in a dangerous para- sible short-term alternative site environment resulting could be the use of indepen- from the natural peripartu- dent culling levels to select rient (prelambing) rise in for internal parasite resis- fecal eggs. tance traits. A performance recording system that can Fecal egg count (FEC) and handle the collection of packed cell volume (PCV) measurements of internal of blood are measurements parasite resistance would be that can be used as a way a critical component. to monitor parasite infec- tion in lambs and in ewes Figure 8. Crossbred lambs. Photo just before lambing and from flickr.com. during lactation. FEC is both a repeatable and heri- can be manifested. How-ev- table trait and does respond er, since research hasshown to selection (Baker et al; that genetic resistance of 1992). Ideally, each time sheep to internal parasites FEC or PCV is measured, is not able to develop until a larval culture should be 5 months of age (Gray et taken to provide an ap- al; 1992), young lambs (1 proximate indication of to 6 months of age) would Figure 7. Yearling purebred Florida which parasite species are need to be dewormed. Native ram. Photo from ARCHIVEwikimedia. present. Sheep producers org. Moreover, since the natu- may negotiate with a local ral resistance ewes have veterinary practice for the The most important issue decreases when they are lab work to be done. Most producers need to face is pregnant, they should be small animal veterinary the requirement of with- given a deworming treat- practices have the neces- holding dewormers from ment about 2 weeks before sary equipment and con- so that genetic lambing. This practice will duct these tests on pets. variation for host resistance prevent placing very young

The Use of Sheep Breeds Resistant to Internal Parasites 3 References Albers, G. A., Gray, G. D., Piper, L. R., Barker, J. S., LeJambre, L. F., & Barger, I. A. (1987, October). The genetics of resistance and resilience to Haemonchus contortus infection in young Merino sheep. International Journal for Parasitology, 17(7), 1355-1363.

Baker, R. L. (1991). Breeding for disease resistance—some historical perspectives, problems and prospects. In: Proceedings of the New Zealand Society of Animal Production, 51, 1-14.

Baker, R. L., Kassi, A. L., Rege, J. E. O., Reynolds, L., Bekele, T., Mukassa-Mugerwa, E., & Rey, B. (1992). A review of genetic resistance to endoparasites in small ruminants and an outline of ILCA’s Research Programme in this area. In: Proceedings of SR-CRSP Science Workshop of the Small Collaborative Research Support Program, Nairobi, Kenya, 10, 79-104.

Baker, R. L., Mwamachi, D. M., Audho, J. O., & Thorpe, W. (1994). Genetic resistance to gastrointestinal parasites in Red Maasai sheep in Kenya. Proceedings of the 5th World Congress on Genetics Applied to Livestock Production, 1-5.

Gray, G. D. (1997, November). The use of genetically resistant sheep to control nematode parasitism. Veterinary Parasitology, 72(3-4), 345-357.

Gruner, L., & Cabaret, J. (1988). Resistance of sheep and to helminth : A genetic basis. In E.F. Thomson, & Thomson, F. S. (eds.), Increasing Small Ruminant Productivity in Semi-arid Areas. The Netherlands.

Ruvuna, F., & Stephens, C. M. (1997). Genetics of resistance to internal parasites with management therapy to utilize anthelmintics in sheep production. Abstracts of the Eleventh Biennial Research Symposium. Association of Research Directors, Inc., 92-93.

Strickland, J. E. (1991). Internal parasite control in sheep. The University of Georgia College of Agricultural and Environmental Sciences/Cooperative Extension Service. Bulletin 1064.

Julio E. Correa, PhD, Extension Animal Scientist & Associate Professor, ARCHIVEAlabama A&M University, and James G. Floyd, DVM, Retired Extension Veterinarian & Professor, and Lisa A. Kriese-Anderson, PhD, Extension Animal Scientist & Associate Professor, Auburn University

For more information, call your county Extension office. Look in your telephone directory under your county’s name to find the number. UNP-0006 The Alabama Cooperative Extension System (Alabama A&M University and Auburn University), is an equal opportunity educator and employer. Everyone is welcome!

Revised February 2016; UNP-0006 © 2016 by Alabama Cooperative Extension System. All rights reserved.