This article presents an investigation that further demonstrates that OPP infection in sheep can be eliminated and controlled by utilizing the agar gel immunodiffusion test and the removal of seropositive sheep from the involved flock. The second approach would consist of testing and placing all reactors in a separate flock on the same premises and obtaining some replacements from the lambs of OPP positive ewes

Light, M.

Ludeman, L.

Schipper, I.A.

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CONTROL OF OVINE PR·OGRESSIVE PNEU MONIA (OPP) LA. Schipper, M. Light and L. Ludeman Surveys have suggested that ovine progressive pneumonia (OPP), frequently referred to as Visna­maedi infection, of cull sheep in western US ranges from 1 percent to 67 percent with a mean of 34.9 percent (4). The incidence in range sheep in Idaho was 16 per­cent in yearlings to 83 percent in ewes over seven years of age (9) . A sero logical incidence of 35.7 percent (high of 67.6 and a low of 20 percent) was recorded in sheep in Quebec, Canada with a 0 to 36.8 percent in infection goats (14). It has been demonstrated that when newborn lambs are removed fro m the ewe and her environment im­mediately following birth and before nursing that the lambs remain free of OPP infection (2, 7, 17). It has also been demonstrated that lambs remaining with OPP infected ewes for 10 hours post-birth were 28 percent in­fected or 76 percent infected if they were with infected ewes until weaning (7). Serum antibody to OPP is not present in the newborn lambs of infected ewes until they have nursed, thus there is no evidence of placental transmission of the OPP virus (22, 23). Antibodies are demonstrable and the OPP virus can be isolated from the colostrum of infected ewes (8, 10, 15, 16, 19,22,23). There are two reports of vertical transmission in utero, but in one case no tests were made until the lambs were four months old so infection could have occured after lambing (1). In the second report OPP virus was reportedly isolated from one lamb fetus (2). It has also been suggested that in utero infection is possible but no proof was offered. (6, 13). A serum neutralization test for OPP was described in 1960 (21). Other serological testing procedures include complement fixation and indirect fluorescent antibody test (8, 11). Indirect immunofluorescence and im­munodiffusion tests can detect specific antibodies before the complement fixing test, but neutralizing an­tibodies appear later than the complement fixation an­tibodies (24). The immunodiffusion test has been reported to be more sensitive then the complement fixa­tion test (3, 5). Immunodiffusion test were reported to be efficacious and have been frequently employed in the detection of OPP infection (4, 18,24). Funding f or this investigation was provided by USDA Special Grant No. 59-2381-1-2-069-0 MATERIAL AND METHODS In an attempt to evaluate two programs for the elimination of OPP from farm or ranch flocks of sheep, cooperating owners were contacted an informed of the potential problems of OPP. Two programs for establishing OPP-free flocks were offered to each owner. Plan A. All sheep including lambs under one year of age were to be bled and the serum tested for OPP by the agar-gel immunodiffusion test (AGIO). Following testing all positive sheep were marketed. A repeat test was to be made at six-month intervals until two negative test were obtained for the flock. Further testing would be at yearly intervals or at the descretion of the owner. Plan B. This plan was designed for those flock owners whose flocks were so extensively infected with OPP that dispersal of all positive sheep would be economically impossible. The sheep were tested as described in plan A, but reactors were either moved to another premise or the OPP-positive flock was separated from the OPP-negative flock but maintained on the same premises. Weaned lambs from the positive flock were placed into the clean flock without test to serve as all or part of the replacements for the establish­ed flock. RESULTS Fifteen cooperators initially indicated interest in this investigation and had their flocks of sheep bled for the AGIO testing for OPP. Of the 15 breeders only four maintained interest to the degree that four test were made on each flock. In the case of these four breeders the testing period lasted four years. Initial testing of 15 flocks indicated that 28.6 percent of 1,989 sheep were seropositive for OPP. One flock of 89 sheep had no detectable OPP infected sheep. The highest infection occured in a flock of 417 with 58.5 per­cent infection. Two breeders utilized the Plan A approach to OPP elimination and continued with the plan for a minimum of four tests. As demonstrated in Table t, when all seropositive sheep were removed from the flocks im­mediately following the determination of their infection 30 TABLE 1 PLAN A DEGREE OF INFECTION Initial Test Second Test Third Test Fo urth Test Flock Infection Size No. 0/ 0 29 7 24.1 29 3 10.3 Fl ock Infeclion Size ..!::!£: % 28 0 0 28 I 3.6 Fl oc k Infection Size No. 0/0 27 0 0 29 0 0 Flock In fect ion Size No. % 27 0 0 29 0 0 status the involved flocks had no further reactors detected following the second test. It will also be noted that the flocks were comparatively small and that the removal of all the seropositive sheep had a minimum economic effect to the owner. Two breaders utilized Plan B. As recorded in Table 2 these were larger flocks than those recorded in Plan A. Though the number of animals seropositive to OPP decreased following the second test, not all seropositive sheep were eliminated up to and including test number four. It should also be noted that the flock size generally decreased following the second testing. TABLE 2 PLAN B DEGREE OF INFECTION Initial 	 FourthSecond Th ird Test Test Tes t Test Flock Infection Flock Infection Flock Infeclion Flock Infection Size No. % Size No. % Size No. % Size No. 0/0 234 67 28.6 234 49 20.9 188 34 18 . 1 163 5 3.1 98 17 17 .3 	 117 19 16.282 17 20.7 	 93 3 3.2 DISCUSSION It is obvious from the various surveys conducted in the United States and Canada that OPP is a serious respiratory disease of sheep and goats (4, 9, 14). It has been suggested that OPP-positive flocks are more sub­ject to other respiratory infections, exibit decreased fer­tility, and do not gain as efficiently as OPP-free flocks (5, 9) . The survey completed in this investigation would indicate that North Dakota has a sufficient flock infec­tion of OPP to conclude that OPP is a serious disease in sheep in this geographical area. It appears that any plan where the OPP-seropositive sheep are removed from the flock will serve to eliminate the OPP problem. When all OPP-seropositive sheep are completely removed from the premises as soon as detected there was a more rapid elimination of the OPP problem then if prolonged or partial removal was employed. The economics of removing all positive sheep and hence the source of infection could be impractical where all or a major part of the producer's income is dependent upon sheep. On the average this would be nearly 29 percent of a North Dakota flock or 35 percent of a flock in the western United States. Separation of OPP-seropositive sheep from OPP­seronegative sheep but maintaining both flocks on the same premises and depending upon untested lambs from the positive flock as replacement subjects the owner to less financial stress but prolongs the process of establishing a totally OPP-free flock. Testing lambs before employing them as clean flock replacements may hasten the process of establishing OPP clean flock, however there is always the possibility that a lamb hav­ing an OPP-negative test may be in the incubative stage of infection and hance not detectable by serodiagnosis (12,13,15,16). Twenty percent of lambs removed from OPP negative ewes immediately following birth and supplied ovine colostrum containing OPP virus became AGIO seropositive within two months of virus ad­ministration (20). Others have also demonstrated col­ostral transmission (I, 3, 13). Though the original plan called for biannual testing until the involved flocks were free of OPP, all owners preferred annual testing as it was more applicable to their management. SUMMARY This investigation further demonstrates that OPP in­fection in sheep can be eliminated and controlled by utilizing the agar gel immunodiffusion test and removal of seropositive sheep from the involved flock. Two ap­proaches may be employed to meet the needs of the sheep producers, one consisting of testing and im­mediate elimination of reactors from the premises and obtaining all replacements from OPP free ewes. The se­cond approach would consist of testing and placing all reactors in a separate flock on the same premises and obtaining some replacements from the lambs of OPP positive ewes . The latter approach will delay the process of elimination of OPP infection in the flock. REFERENCES 1. 	 Cross, R.F., Smith , C.K.: Vertical Transmission of Pro­gressive Pneumonia in Sheep. Am. J. Vet. Res . 36( 1975):465-468. 2. Cutlip, R.C., Lehmkuhl , H.D., Jackson, T.A .: in­trauterine Transmission of Ovine Progressive Pneumonia Virus. Am. J . Vet. Res. 42(1981): 1795-1797. 3. 	Cutlip, R.C., Jackson, T.A., Lehmkuhl, H.D.: Diagnostic Features of Ovine Progressive Pneumonia. JAVMA 173(1978):1578-1579. 4. 	 Cutlip, R.C., Jackson, T.A., Laird, G.A.: Prevalence of Ovine Progressive Pneumonia in a Sampling of Cull Sheep from Western U.S. Am. J. Vet. Res . 38(1977):2091-2093. Continued on page 3531 to a smaller amount of water lost as evaporation early in the growing season and a more favorable soil water status during the growing season. SUMMARY This research supports . the value of small grain residue for water conservation. The most significant benefit was from snow trapping and subsequent in­crease in soil water content. In addition, the stubble reduced stage one evaporation losses during rainy periods. In general the evapotranspiration from NE was less than NW until the first week of JUly. After this the evapotranspiration from NE became greater because of greater soil water availability for transpiration. The cumulative water use became equal on July 19; however, for the growing season NE used 2.67 inches more water than NW resulting in 7.8 bushels per acre greater soybean yield. REFERENCES Black, A.L. and F. H. Siddoway. 1979. Innuence of tillage and wheat straw residue management on soil properties in the Great Plains. J. Soil and Water Cons. 34(5):220-223. Bond, J .J . and W.O. Willis; 1969. Soil water evaporation: surface residue and placement effects. Soil Sci. Soc. Amer. J. 33:445-448. Brun, L.J . , J.W. Enz and J.K . Larsen. 1983. Climatic research in the Department of Soil Science. ND Farm Res. 41(1):9-11 and 23 . Collins, D. 1982. Achieving cost-effective conservation. J . of ~oil and Water Cons. 37(5):262-263 . French, E.W . and N. Riveland. 1980. Chemical fallow in a spring wheat-fallow rotation. ND Farm Res . 38(1) :12-15. Greb, B.W., D.E. Smika and A.L. Black . 1967. Effect of straw mulch rates on soil water storage during summer fallow in the Great Plains. Soil Sci . Soc. Am. J . 31 :556-559. Smika, D.E. 1983 . Soil water change as related to position of wheat straw mulch on the soil surface. Soil Sci . Soc . Amer. J.47:988-991. Continued from page 31 5. 	 Dawson, M. : Maedi/ Visna: A review. Vet. Rec. 106(1980):212-216. 6. 	DeBoer, F.G., Houwers, D.J . : Epizootiology of Maedi / Visna in Sheep. In Tyrrel, D.A.J. (ed): Aspects of Slow and Persistant Virus Infections. ECSC, EEC, EAEC, Brussels-Luxembourg (1979): 198-220. 7. DeBoer, G .F., C. Terpstra, D.J. Houwers : Studies in EpidemiJolgy of Maedi/Visna in Sheep. Res. Vet. Sci . 26( 1979) :202-208. 8. DeBoer, 	G.F.: Antibody Formation in Zwoegerziekte, A Slow Infection in Sheep . J . Imm. 104(1970):414-422. 9. 	 Gates, N.L., Winward, L.D., Gorham, J.R., Shen, D.T.: Serologic Survey of Prevalence of Ovine Pro­gressive Pneumonia in Idaho Range Sheep . JA VMA, 173(1978):1575-1577. 10. 	 Gudnadotlir, M.: Visna-Maedi in Sheep. Progr. Med. Virol. 18(1974):336-349. 11. 	Gudnadotlir , M., Kristinsdottir, K.: Complement-Fixing AntibOdies in Sera of Sheep Affected with Visna and Maedi. J. Immun . 98(1967):663-667. 12. 	 Hoff-Jorgensen, R.: Slow Virus Infections with Par­ticular Reference to Maedi- Visna and Enzootic Bovine Leukemia. Vel. Sci. Commun. 1(1977):251-263. 13. 	 Lamontagne, L., Girard, R.A., Samagh, B.S.: Seroepi­demiological Survey of Maedi / Visna Virus Infection in Sheep and Goat Flocks in Quebec. Can. J . Compo Med. 47(1983): 309-315. 14. Larsen, H.J., Hy\lseth, B., Krogsrud, J.: Experimental Maedi Virus Infection in Sheep: Early Cellular and Humoral Immne Response Following Parenteral In­oculation . Am. J. Vel. Res. 43(1982):379-383. 15. 	 Larsen, H.J., Hyllseth, B., Krogsrud, J.: Experimental Maedi Virus Infection in Sheep: Cellular and Humoral Immune Response During Three Years following In­tranasal Inoculation. Am. J . Vet. Res. 43(1982) :384-389. 16. 	 Light, M.R., Schipper, LA., Molitor, T.W ., Tilton, . J.E., Sianger, W.D.: Progressive Pneumonia in Sheep : Incidence of Natural Infection and Establishiment of Clean Flocks. 1. An . Sci. 49(1979):1157-1160. 17. Molitor, T .W., Schipper, LA., Berryhill, D.L., Light, M.R.: Evaluation of the Agargel Immunodiffusion Test for the Detection of Precipitating Antibodies Against Progressive Pneumonia Virus of Sheep. Can . J . Comp o Med . 43(1979) :280-287. 18. 	Palsson, P .A . : Maedi and Visna in Sheep. Front BioI. 44(1976): 17-43. 19. 	 Vaheim, K. L., Schipper, LA.: Detection of Colostral Antibodies to Ovine Progressive Pneumonia Virus. N. Dak. Farm Research 41(1981) :26-27. 20 . 	Sigurdsson, B., Thormar, H. and Palsson, P .A.: Cultivation of Visna Virus in Tissue Culture. Archiv fur die Gesamte Virus forschung 10(1960):368-381. 21. Sihvonen, L.: Early 	Immune Responses in Experimental Maedi . Res. Vet. Sci. 30(1981): 217-222. 22 . 	Sihvonen, L.: Studies on Transmission of Maedi Virus to Lambs. Acta Vel. Scand. 21 (1980):689-698. 23. 	Terpestra, c., Deboer, G.F. : Precipitating Antibodies Against Maedi-Visna Virus in Experimentally Infected Sheep. Arch. Ges. Virusforsch 43(1973):53-62. 24. 	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Control of Ovine Progressive Pneumonia

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