Veterinary Parasitology, 42 (1992) 257-263 Elsevier Science Publishers B.V., Amsterdam
257
Evaluation of ivermectin agfiinst experimental infections of Haemonchus contortus and Trichostrongylus colubriformis in goats P.G. Hoyt a, D.D. Frenchb, J.E. Millerc, J.C. Williams b, G.E. Hackett, Jr. a, M.T. Kearneyc and M.J. HoyV aDepartment of Veterinary Clinical Science, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA bDepartment of Veterinary Science, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA CDepartment of Epidemiology and Community Health, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA dCalifornia State Polytechnic University, Pomona, CA 91768-4076, USA eSchool of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA (Accepted 4 November 1991 )
ABSTRACT Hoyt, P.G., French, D.D., Miller, J.E., Williams, J.C., Hackett, Jr., G.E., Kearney, M.T. and Hoyt, M.J., 1992. Evaluation of ivermectin against experimental infections of Haemonchus contortus and Trichostrongylus colubriformis in goats. Vet. Parasitol., 42: 257-263. Fourteen nematode parasite-naive kids were given a mixed larval inoculum (approximately 17 250 infective larvae) via stomach tube. Twenty-two days after infection, the kids were randomly assigned to control and treatment groups of seven animals each. Mean eggs per gram for control and treatment groups were 4304 and 5315, respectively. Kids in the treatment group were given ivermectin (0.2 mg kg- ~) administered by subcutaneous injection. At necropsy, the mean numbers of Haemonchus contortus and Trichostrongylus colubriformis for control and treatment groups were 2259 and 0, and 3033 and 773, respectively. This reduction was significant (P< 0.05) for both species, resulting in an efficacy of 100.0% and 74.5%, respectively. The lower efficacy against T. colubriformis may be a sign of resistance, a reduced effectiveness due to route of administration, or a higher dose may be required with subcutaneous administration, as has been observed previously.
INTRODUCTION
On a world-wide basis, goats are of great economic importance (Hagstad et al., 1984 ). There are many conflicting goat population figures available for the United States. The 1987 Agricultural Census listed 45 032 goat farms and Correspondence to: Dr. P.G. Hoyt, Department of Clinical Science, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-4017/92/$05.00
258
P.G. HOYTETAL.
a goat population of 2 246 587. In 1989 the Agricultural Stabilization and Conservation Service listed 2 321 000 Angora goats in the United States (Anonymous, 1989 ). The yearly registration of dairy goats has increased from 3611 in 1955 (Leach, 1980) to 35 779 in 1990 (Miller, 1991 ). These figures do indicate that goat ownership is very popular within the United States. Gastrointestinal nematodes are considered a major health problem in goat herds, especially when increased stocking rates result in increased nematode burdens (Baker, 1975; Lutu, 1983; Kettle et al., 1983; LeJambre, 1984; McKenna, 1984). Most management programs employ the routine use of anthelmintics because goats do not appear to develop a stable or lasting immunity to gastrointestinal nematodes (Baker, 1975; LeJambre and Royal, 1976; Lutu, 1983; Kettle et al., 1983; LeJambre, 1984; McKenna, 1984; Hagstad et al., 1984). Use of anthelmintics in goats has resulted in nematode resistance to some benzimidazoles, levamisole, and morantel tartrate (Lutu, 1983; Kettle et al., 1983; McKenna, 1984). Dose rates of these drugs are the same for sheep and goats even though plasma levels are lower and excretion rates are more rapid in goats (McKenna, 1984; Swan and Gross, 1985). Therefore, current dose rates may be inappropriate for goats, and the anthelmintic resistance phen o m e n o n may actually be an anthelmintic ineffectiveness (McKenna, 1984 ). As anthelmintic resistance or anthelmintic ineffectiveness becomes more prevalent, control of gastrointestinal parasites will become more difficult. Ivermectin, administered by subcutaneous injection (the most c o m m o n method used by producers) had been used for gastrointestinal nematode parasite control in the goat herd maintained at the School of Veterinary Medicine, Louisiana State University, for 3 years. Efficacy, based on fecal egg per gram (EPG) counts, decreased from year to year. The purpose of this study was to evaluate the efficacy of ivermectin administered by subcutaneous injection. MATERIALS AND METHODS
Fifteen pregnant does, maintained on pasture, were dewormed with ivermectin (Ivomec ®, 0.2 mg kg-1 administered by subcutaneous injection) approximately 14 days before kidding and again 7 days later. Immediately after kidding, the does and their l 5 kids were moved to a pen with a well-drained concrete floor, and the does were dewormed with ivermectin weekly. Water was available ad libitum and the does were fed 3 lb of a complete pelleted ration daily while confined. The concrete floor was washed daily to remove fecal matter. All kids, at approximately 4 weeks of age, were vaccinated for Clostridium perfringens types C and D, and the males were castrated and received tetanus antitoxin. The kids were weaned as a group at approximately 5 weeks of age
USE OF IVERMECT1N FOR PARASITE CONTROL IN GOATS
259
and remained on the concrete floor. The does were moved back to pasture. Water and a complete pelleted ration were available for the kids at all times. Feces from seven untreated does were collected, mixed with water and vermiculite in plastic pans, and covered with aluminum foil. These cultures were maintained at 24°C for 14 days and then subjected to the Baermann technique for harvesting of infective larvae. There were 16 125 infective larvae (84% Trichostrongylus and 16% Haemonchus) recovered. These larvae were inoculated via stomach tube into one of the nematode-na'fve kids. Twentyeight days after the infection of this donor kid, its feces were collected and cultured. Larvae were harvested, identified to genera, counted, and stored at 4°C. Fecal samples were collected from each of the remaining 14 kids 38 and 9 days before and on the day of experimental inoculation and were processed by the double centrifugation-flotation technique using concentrated sugar solution to determine EPG counts. On the day of inoculation, the kids as a group were approximately 4 months of age. Each of the kids was given a mixed larval inoculum via stomach tube containing approximately 17 250 infective larvae (37.7% H. contortus and 62.3% T. colubriformis). The kids were randomly assigned to control and treatment groups (seven animals each). Fecal samples were collected 22 days after inoculation to determine patency of infection; the treatment group received ivermectin (0.2 mg kg -1 ) by subcutaneous injection, and the control group received no treatment. The two groups were maintained in separate adjacent pens which had well-drained concrete floors. One control animal died 21 days after infection, and two other control animals had to be killed before the end of the study because of their anemic condition. Twelve days after treatment, all remaining animals were stunned with a captive-bolt gun, exsanguinated, and necropsied. At necropsy, the pylorus, ileocecal valve, and rectum were ligated, and the abomasum and small intestine were separated. The large intestine was not examined. The abomasum and small intestine were opened and the contents washed into separate containers for each organ. Water was added until a total volume of 71 was obtained. While being stirred, a 1 1 aliquot from each container was removed and preserved in 5% formalin. The abomasum was soaked in water overnight at 24°C. The mucosa was then washed and scraped. Water was added to the scrapings until a total volume of 4 1 was reached. A 500 ml aliquot was taken and preserved in 5% formalin. A 200 ml portion of each aliquot was examined, and all nematode parasites found were counted. All nematodes, or the first 100, were identified for population distribution determination. For calculation of nematode counts in the abomasum and small intestine, and total count, the number of nematodes counted in each aliquot was multiplied by the appropriate aliquoting factors. For calculation of the nematode
260
P.G. HOYT ETAL.
population distribution, the total nematode count for each organ was multiplied by the percentage of each species identified. The non-parametric Wilcoxon Rank Sum test was used to statistically evaluate differences in nematode species between control and treated groups. RESULTS
Kids were minimally parasitized (2 EPG or less) for the 38 days prior to being experimentally infected (Table 1 ). Mean EPG counts for control and treatment groups, 22 days after infection, were 4304 and 5315. Mean counts for control and treatment groups 5 days after treatment were 6134 and 62, respectively, and 12 days after treatment mean counts were 4238 and 64, respectively. Efficacy, based on EPG counts, at 5 and 12 days after treatment was 99.0% and 98.5%, respectively. The mean parasite numbers recovered from the control and treatment groups were 2259 and 0 (H. contortus) and 3033 and 773 ( T. colubriformis) (Table 2). These differences were significantly ( P < 0.05 ) different for each parasite species. Efficacy ofivermectin against H. contortus and T. colubriformis was 100.0% and 74.5%, respectively. The numbers of Trichostrongylus TABLE1 M e a n n e m a t o d e egg per g r a m ( E P G ) c o u n t s in feces o f control a n d treated goat kids following experi m e n t a l infection with Haemonchus contortus a n d Trichostrongylus colubriformis Day of infection
Treatment group
No. o f animals
EPG ( M e a n _+SD )
- 38
Control Treated Control Treated Control Treated Control Treated Control Treated Control Treated
7 7 7 7 5 7 6 5 5 7 4 7
0.86 +_ 1.50 0.86_+ 1.50 0.14_+0.38 0.14 _+0.38 1.60 _+2.30 1.14_+ 0.90 4304_+ 4262 5315 _+3778 6134 _+5660 62 _+96 4238_+ 5960 64 +_89
-
9 02 223 27 34
Efficacy ~
99.0 98.5
Control a n i m a l s died or were killed 21, 23 a n d 27 days after infection. calculated as M e a n E P G in c o n t r o l - m e a n E P G in treated t Efficacy : M e a n E P G in control × 100. 2Day 0, e x p e r i m e n t a l infection; each a n i m a l inoculated with a p p r o x i m a t e l y 17 250 infective larvae ( 37.7% H. contortus a n d 62.3% T. colubriformis ). 3Day o f t r e a t m e n t .
USE OF IVERMECTIN FOR PARASITE CONTROL IN GOATS
261
TABLE 2 Efficacy o f i v e r m e c t i n (0.2 m g k g - l s u b c u t a n e o u s l y ) against e x p e r i m e n t a l infections o f H a e m o n c h u s contortus a n d Trichostrongylus colubriformis in goat kids N e m a t o d e species
No. o f n e m a t o d e s Control (n = 7 ) ( m e a n + SD )
Haemonchus contortus Trichostrongylus colubriformis Trichostrongylus axei Ostertagia spp.
2259a+ 1283 3033 a + 1289 3a+ 2a+
5 4
Efficacy Treated (n = 7 ) ( m e a n + SD ) 0b
100.0
773 b + 1009 0~ 5 ~+
13
74.5 -
M e a n no. in c o n t r o l - m e a n no. in treated × 100. M e a n no. in control M e a n s in the s a m e row with different superscripts are significantly different ( P < 0.05 ). Efficacy calculated as:
axei and Ostertagia spp. recovered from the kids were too small for a valid determination of efficacy. DISCUSSION
The inoculation of 17 250 larvae (37.7% H. contortus) may have been excessive for this age group of kids, in that three of the control animals either died or were killed because of anemia before the rest of the animals were necropsied. Ivermectin has a federal license, in the US, for internal parasite control in horses, cattle, sheep, and swine, but it is not cleared for use in goats. However, ivermectin has been reported to have broad spectrum anthelmintic activity in goats. An oral dose of 0.3 mg kg -~ had an efficacy of 100% against all gastrointestinal nematodes (Anonymous, 1982). Oral dosages of 0.05-0.2 mg kg- 1 had an efficacy of more than 96.9% against H. contortus and T. colubriformis (Swan and Gross, 1985 ). A subcutaneous dose of 0.2 mg kg- ~ had an efficacy of 100% against H. contortus (Njanja et al., 1987). An oral dose of 0.2 mg kg- i had an efficacy of more than 99.0% against H. contortus, Ostertagia spp., T. colubriformis, and Cooperia curticei (McKenna and Watson, 1987). The low efficacy against T. colubriformis could be suspected as evidence of resistance to ivermectin. Ivermectin had been used for nematode parasite control in this herd for 3 years prior to the study. Resistance of H. contortus and T. colubriformis to ivermectin has been reported in sheep (Van Wyk and Malan, 1988; Giordano et al., 1988 ). The low efficacy could also be associated with the route of administration.
262
P.O. HOYT ET AL.
Oral administration (0.15 mg k g - i ) in lambs was more efficacious than the subcutaneous (0.2 mg kg-~ ) route (Giordano et al., 1988 ). Oral administration (0.2 mg kg -~ ) in goats had a 100% efficacy in the reduction of fecal egg counts while the same dose given subcutaneously had a 94% efficacy (Pearson and Rutherford, 1988). An efficacy against T. colubriformis in goats of more than 97% has been reported with oral administration (Anonymous, 1982; Swan and Gross, 1985; M c K e n n a and Watson, 1987). A difference in efficacy in goats was noted when comparing the reduction of fecal egg counts after subcutaneous and oral administration (94% and 100%, respectively), suggesting that subcutaneous administration may not be appropriate for controlling Trichostrongylus spp. infection (Pearson and Rutherford, 1988 ). There also is evidence that ivermectin is more effective in the abomasum than in the small intestine. It has been shown that a m u c h smaller dose is required to control T. axei in the a b o m a s u m than T. colubriformis in the small intestine of cattle with either oral or subcutaneous administration (Egerton et al., 1981 ). This was also demonstrated in sheep when a subcutaneous dose of 0.2 mg kg-~ had good efficacy against abomasal nematodes but lower efficacy against small intestinal parasites (Wescott and LeaMaster, 1982). It has been suggested that this reduced efficacy against small intestinal nematodes may be explained by the parasites recovering from the effects of the drug and re-establishing at the distal end of the small intestine (Bogan et al., 1988). With the 100% reduction in H. contortus, this study demonstrated that the subcutaneous injection of ivermectin (0.2 mg kg -~ ) is an extremely efficacious treatment for young goats infected with this parasite. The 74.5% reduction in T. colubriformis in the present study could indicate a parasite resistance, a reduced effectiveness against this parasite with subcutaneous administration, or that a higher subcutaneous dose may be required for small intestinal parasites. To determine if a true resistance is present, further work is required, comparing oral with subcutaneous administration and increasing the subcutaneous dose for the small intestinal parasites.
REFERENCES Anonymous, 1982. Ivermectins in goats. Surveillance, 9: 22-24. Anonymous, 1989. Mohair production figures released. Ranch Mag., 70 (9): 53. Baker, N.F., 1975. Control of parasitic gastroenteritis in goats. J. Am. Vet. Med. Assoc., 167: 1069-1075. Bogan, J.A., McKellar,Q.A., Mitchell, E.S. and Scott, E.W., 1988. Efficacyof ivermectin against Cooperia curticei infection in sheep. Am. J. Vet. Res., 49 ( 1): 99-100. Egerton, J.R., Eary, C.H. and Suhayda, D., 1981. The anthelmintic efficacy of ivermectin in experimentally infected cattle. Vet. Parasitol., 8: 59-70. Giordano, D.J., Tritschler, II, J.P. and Coles, G.C., 1988. Selection of ivermectin-resistant Trichostrongylus colubriformisin lambs. Vet. Parasitol., 30:139-148.
USE OF IVERMECTIN FOR PARASITE CONTROL IN GOATS
263
Hagstad, H.V., Hubbert, W.T. and Craig, L.M., 1984. Health status as related to management practices in Louisiana goat herds. Int. Goat Sheep Res., 2: 238-242. Kettle, P.R., Vlassoff, A., Reid, T.C. and Horton, C.T., 1983. A survey of nematode control measures used by milking goat farmers and of anthelmintic resistance on their farms. N.Z. Vet. J., 31: 139-143. Leach, K., 1980. Trends in dairy goats. J. Dairy Sci., 63: 1600-1604. LeJambre, L.F., 1984. Stocking rate effects on the worm burdens of Angora goats and Merino sheep. Aust. Vet. J., 61: 280-282. LeJambre, L.F. and Royal, W.M., 1976. A comparison of worm burdens in grazing Merino sheep and Angora goats. Aust. Vet. J., 52:181-183. Lutu, W.Z., 1983. Internal parasitism in milk goats in Kenya. Trop. Anim. Health Prod., 16: 153-157. McKenna, P.B., 1984. Gastro-intestinal parasitism and "anthelmintic resistance" in goats. Surveillance, 1 t: 2-4. McKenna, P.B. and Watson, T.G., 1987. The comparative efficacy of four broad spectrum anthelmintics against some experimentally induced trichostrongylid infections in sheep and goats. N.Z. Vet. J., 35: 192-195. Miller, A.J., 1991. Bleatings: Report from ADGA office. Dairy Goat J., 69 (3): 5. Njanja, J.C., Wescott, R.B. and Ruvuna, F., 1987. Comparison ofivermectin and thiabendazole for treatment of naturally occurring nematode infections of goats in Kenya. Vet. Parasitol., 23: 205-209. Pearson, A.B. and Rutherford, D.M., 1988. Ivermectin injection less effective in goats than oral treatment. Surveillance, 15: 22. Swan, G.E. and Gross, S.J., 1985. Efficacy of ivermectin against induced gastrointestinal nematode infections in goats. Vet. Rec., 117:147-149. Van Wyk, J.A. and Malan, F.S., 1988. Resistance of field strains ofHaemonchus contortus to ivermectin, closantel, rafoxanide and the benzimidazoles in South Africa. Vet. Rec., 123: 226-228. Wescott, R.B. and LeaMaster, B.R., 1982. Efficacy ofivermectin against naturally acquired and experimentally induced nematode infections in sheep. Am. J. Vet. Res., 43 (3): 531-533.
257
Evaluation of ivermectin agfiinst experimental infections of Haemonchus contortus and Trichostrongylus colubriformis in goats P.G. Hoyt a, D.D. Frenchb, J.E. Millerc, J.C. Williams b, G.E. Hackett, Jr. a, M.T. Kearneyc and M.J. HoyV aDepartment of Veterinary Clinical Science, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA bDepartment of Veterinary Science, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA CDepartment of Epidemiology and Community Health, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA dCalifornia State Polytechnic University, Pomona, CA 91768-4076, USA eSchool of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA (Accepted 4 November 1991 )
ABSTRACT Hoyt, P.G., French, D.D., Miller, J.E., Williams, J.C., Hackett, Jr., G.E., Kearney, M.T. and Hoyt, M.J., 1992. Evaluation of ivermectin against experimental infections of Haemonchus contortus and Trichostrongylus colubriformis in goats. Vet. Parasitol., 42: 257-263. Fourteen nematode parasite-naive kids were given a mixed larval inoculum (approximately 17 250 infective larvae) via stomach tube. Twenty-two days after infection, the kids were randomly assigned to control and treatment groups of seven animals each. Mean eggs per gram for control and treatment groups were 4304 and 5315, respectively. Kids in the treatment group were given ivermectin (0.2 mg kg- ~) administered by subcutaneous injection. At necropsy, the mean numbers of Haemonchus contortus and Trichostrongylus colubriformis for control and treatment groups were 2259 and 0, and 3033 and 773, respectively. This reduction was significant (P< 0.05) for both species, resulting in an efficacy of 100.0% and 74.5%, respectively. The lower efficacy against T. colubriformis may be a sign of resistance, a reduced effectiveness due to route of administration, or a higher dose may be required with subcutaneous administration, as has been observed previously.
INTRODUCTION
On a world-wide basis, goats are of great economic importance (Hagstad et al., 1984 ). There are many conflicting goat population figures available for the United States. The 1987 Agricultural Census listed 45 032 goat farms and Correspondence to: Dr. P.G. Hoyt, Department of Clinical Science, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-4017/92/$05.00
258
P.G. HOYTETAL.
a goat population of 2 246 587. In 1989 the Agricultural Stabilization and Conservation Service listed 2 321 000 Angora goats in the United States (Anonymous, 1989 ). The yearly registration of dairy goats has increased from 3611 in 1955 (Leach, 1980) to 35 779 in 1990 (Miller, 1991 ). These figures do indicate that goat ownership is very popular within the United States. Gastrointestinal nematodes are considered a major health problem in goat herds, especially when increased stocking rates result in increased nematode burdens (Baker, 1975; Lutu, 1983; Kettle et al., 1983; LeJambre, 1984; McKenna, 1984). Most management programs employ the routine use of anthelmintics because goats do not appear to develop a stable or lasting immunity to gastrointestinal nematodes (Baker, 1975; LeJambre and Royal, 1976; Lutu, 1983; Kettle et al., 1983; LeJambre, 1984; McKenna, 1984; Hagstad et al., 1984). Use of anthelmintics in goats has resulted in nematode resistance to some benzimidazoles, levamisole, and morantel tartrate (Lutu, 1983; Kettle et al., 1983; McKenna, 1984). Dose rates of these drugs are the same for sheep and goats even though plasma levels are lower and excretion rates are more rapid in goats (McKenna, 1984; Swan and Gross, 1985). Therefore, current dose rates may be inappropriate for goats, and the anthelmintic resistance phen o m e n o n may actually be an anthelmintic ineffectiveness (McKenna, 1984 ). As anthelmintic resistance or anthelmintic ineffectiveness becomes more prevalent, control of gastrointestinal parasites will become more difficult. Ivermectin, administered by subcutaneous injection (the most c o m m o n method used by producers) had been used for gastrointestinal nematode parasite control in the goat herd maintained at the School of Veterinary Medicine, Louisiana State University, for 3 years. Efficacy, based on fecal egg per gram (EPG) counts, decreased from year to year. The purpose of this study was to evaluate the efficacy of ivermectin administered by subcutaneous injection. MATERIALS AND METHODS
Fifteen pregnant does, maintained on pasture, were dewormed with ivermectin (Ivomec ®, 0.2 mg kg-1 administered by subcutaneous injection) approximately 14 days before kidding and again 7 days later. Immediately after kidding, the does and their l 5 kids were moved to a pen with a well-drained concrete floor, and the does were dewormed with ivermectin weekly. Water was available ad libitum and the does were fed 3 lb of a complete pelleted ration daily while confined. The concrete floor was washed daily to remove fecal matter. All kids, at approximately 4 weeks of age, were vaccinated for Clostridium perfringens types C and D, and the males were castrated and received tetanus antitoxin. The kids were weaned as a group at approximately 5 weeks of age
USE OF IVERMECT1N FOR PARASITE CONTROL IN GOATS
259
and remained on the concrete floor. The does were moved back to pasture. Water and a complete pelleted ration were available for the kids at all times. Feces from seven untreated does were collected, mixed with water and vermiculite in plastic pans, and covered with aluminum foil. These cultures were maintained at 24°C for 14 days and then subjected to the Baermann technique for harvesting of infective larvae. There were 16 125 infective larvae (84% Trichostrongylus and 16% Haemonchus) recovered. These larvae were inoculated via stomach tube into one of the nematode-na'fve kids. Twentyeight days after the infection of this donor kid, its feces were collected and cultured. Larvae were harvested, identified to genera, counted, and stored at 4°C. Fecal samples were collected from each of the remaining 14 kids 38 and 9 days before and on the day of experimental inoculation and were processed by the double centrifugation-flotation technique using concentrated sugar solution to determine EPG counts. On the day of inoculation, the kids as a group were approximately 4 months of age. Each of the kids was given a mixed larval inoculum via stomach tube containing approximately 17 250 infective larvae (37.7% H. contortus and 62.3% T. colubriformis). The kids were randomly assigned to control and treatment groups (seven animals each). Fecal samples were collected 22 days after inoculation to determine patency of infection; the treatment group received ivermectin (0.2 mg kg -1 ) by subcutaneous injection, and the control group received no treatment. The two groups were maintained in separate adjacent pens which had well-drained concrete floors. One control animal died 21 days after infection, and two other control animals had to be killed before the end of the study because of their anemic condition. Twelve days after treatment, all remaining animals were stunned with a captive-bolt gun, exsanguinated, and necropsied. At necropsy, the pylorus, ileocecal valve, and rectum were ligated, and the abomasum and small intestine were separated. The large intestine was not examined. The abomasum and small intestine were opened and the contents washed into separate containers for each organ. Water was added until a total volume of 71 was obtained. While being stirred, a 1 1 aliquot from each container was removed and preserved in 5% formalin. The abomasum was soaked in water overnight at 24°C. The mucosa was then washed and scraped. Water was added to the scrapings until a total volume of 4 1 was reached. A 500 ml aliquot was taken and preserved in 5% formalin. A 200 ml portion of each aliquot was examined, and all nematode parasites found were counted. All nematodes, or the first 100, were identified for population distribution determination. For calculation of nematode counts in the abomasum and small intestine, and total count, the number of nematodes counted in each aliquot was multiplied by the appropriate aliquoting factors. For calculation of the nematode
260
P.G. HOYT ETAL.
population distribution, the total nematode count for each organ was multiplied by the percentage of each species identified. The non-parametric Wilcoxon Rank Sum test was used to statistically evaluate differences in nematode species between control and treated groups. RESULTS
Kids were minimally parasitized (2 EPG or less) for the 38 days prior to being experimentally infected (Table 1 ). Mean EPG counts for control and treatment groups, 22 days after infection, were 4304 and 5315. Mean counts for control and treatment groups 5 days after treatment were 6134 and 62, respectively, and 12 days after treatment mean counts were 4238 and 64, respectively. Efficacy, based on EPG counts, at 5 and 12 days after treatment was 99.0% and 98.5%, respectively. The mean parasite numbers recovered from the control and treatment groups were 2259 and 0 (H. contortus) and 3033 and 773 ( T. colubriformis) (Table 2). These differences were significantly ( P < 0.05 ) different for each parasite species. Efficacy ofivermectin against H. contortus and T. colubriformis was 100.0% and 74.5%, respectively. The numbers of Trichostrongylus TABLE1 M e a n n e m a t o d e egg per g r a m ( E P G ) c o u n t s in feces o f control a n d treated goat kids following experi m e n t a l infection with Haemonchus contortus a n d Trichostrongylus colubriformis Day of infection
Treatment group
No. o f animals
EPG ( M e a n _+SD )
- 38
Control Treated Control Treated Control Treated Control Treated Control Treated Control Treated
7 7 7 7 5 7 6 5 5 7 4 7
0.86 +_ 1.50 0.86_+ 1.50 0.14_+0.38 0.14 _+0.38 1.60 _+2.30 1.14_+ 0.90 4304_+ 4262 5315 _+3778 6134 _+5660 62 _+96 4238_+ 5960 64 +_89
-
9 02 223 27 34
Efficacy ~
99.0 98.5
Control a n i m a l s died or were killed 21, 23 a n d 27 days after infection. calculated as M e a n E P G in c o n t r o l - m e a n E P G in treated t Efficacy : M e a n E P G in control × 100. 2Day 0, e x p e r i m e n t a l infection; each a n i m a l inoculated with a p p r o x i m a t e l y 17 250 infective larvae ( 37.7% H. contortus a n d 62.3% T. colubriformis ). 3Day o f t r e a t m e n t .
USE OF IVERMECTIN FOR PARASITE CONTROL IN GOATS
261
TABLE 2 Efficacy o f i v e r m e c t i n (0.2 m g k g - l s u b c u t a n e o u s l y ) against e x p e r i m e n t a l infections o f H a e m o n c h u s contortus a n d Trichostrongylus colubriformis in goat kids N e m a t o d e species
No. o f n e m a t o d e s Control (n = 7 ) ( m e a n + SD )
Haemonchus contortus Trichostrongylus colubriformis Trichostrongylus axei Ostertagia spp.
2259a+ 1283 3033 a + 1289 3a+ 2a+
5 4
Efficacy Treated (n = 7 ) ( m e a n + SD ) 0b
100.0
773 b + 1009 0~ 5 ~+
13
74.5 -
M e a n no. in c o n t r o l - m e a n no. in treated × 100. M e a n no. in control M e a n s in the s a m e row with different superscripts are significantly different ( P < 0.05 ). Efficacy calculated as:
axei and Ostertagia spp. recovered from the kids were too small for a valid determination of efficacy. DISCUSSION
The inoculation of 17 250 larvae (37.7% H. contortus) may have been excessive for this age group of kids, in that three of the control animals either died or were killed because of anemia before the rest of the animals were necropsied. Ivermectin has a federal license, in the US, for internal parasite control in horses, cattle, sheep, and swine, but it is not cleared for use in goats. However, ivermectin has been reported to have broad spectrum anthelmintic activity in goats. An oral dose of 0.3 mg kg -~ had an efficacy of 100% against all gastrointestinal nematodes (Anonymous, 1982). Oral dosages of 0.05-0.2 mg kg- 1 had an efficacy of more than 96.9% against H. contortus and T. colubriformis (Swan and Gross, 1985 ). A subcutaneous dose of 0.2 mg kg- ~ had an efficacy of 100% against H. contortus (Njanja et al., 1987). An oral dose of 0.2 mg kg- i had an efficacy of more than 99.0% against H. contortus, Ostertagia spp., T. colubriformis, and Cooperia curticei (McKenna and Watson, 1987). The low efficacy against T. colubriformis could be suspected as evidence of resistance to ivermectin. Ivermectin had been used for nematode parasite control in this herd for 3 years prior to the study. Resistance of H. contortus and T. colubriformis to ivermectin has been reported in sheep (Van Wyk and Malan, 1988; Giordano et al., 1988 ). The low efficacy could also be associated with the route of administration.
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Oral administration (0.15 mg k g - i ) in lambs was more efficacious than the subcutaneous (0.2 mg kg-~ ) route (Giordano et al., 1988 ). Oral administration (0.2 mg kg -~ ) in goats had a 100% efficacy in the reduction of fecal egg counts while the same dose given subcutaneously had a 94% efficacy (Pearson and Rutherford, 1988). An efficacy against T. colubriformis in goats of more than 97% has been reported with oral administration (Anonymous, 1982; Swan and Gross, 1985; M c K e n n a and Watson, 1987). A difference in efficacy in goats was noted when comparing the reduction of fecal egg counts after subcutaneous and oral administration (94% and 100%, respectively), suggesting that subcutaneous administration may not be appropriate for controlling Trichostrongylus spp. infection (Pearson and Rutherford, 1988 ). There also is evidence that ivermectin is more effective in the abomasum than in the small intestine. It has been shown that a m u c h smaller dose is required to control T. axei in the a b o m a s u m than T. colubriformis in the small intestine of cattle with either oral or subcutaneous administration (Egerton et al., 1981 ). This was also demonstrated in sheep when a subcutaneous dose of 0.2 mg kg-~ had good efficacy against abomasal nematodes but lower efficacy against small intestinal parasites (Wescott and LeaMaster, 1982). It has been suggested that this reduced efficacy against small intestinal nematodes may be explained by the parasites recovering from the effects of the drug and re-establishing at the distal end of the small intestine (Bogan et al., 1988). With the 100% reduction in H. contortus, this study demonstrated that the subcutaneous injection of ivermectin (0.2 mg kg -~ ) is an extremely efficacious treatment for young goats infected with this parasite. The 74.5% reduction in T. colubriformis in the present study could indicate a parasite resistance, a reduced effectiveness against this parasite with subcutaneous administration, or that a higher subcutaneous dose may be required for small intestinal parasites. To determine if a true resistance is present, further work is required, comparing oral with subcutaneous administration and increasing the subcutaneous dose for the small intestinal parasites.
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Hagstad, H.V., Hubbert, W.T. and Craig, L.M., 1984. Health status as related to management practices in Louisiana goat herds. Int. Goat Sheep Res., 2: 238-242. Kettle, P.R., Vlassoff, A., Reid, T.C. and Horton, C.T., 1983. A survey of nematode control measures used by milking goat farmers and of anthelmintic resistance on their farms. N.Z. Vet. J., 31: 139-143. Leach, K., 1980. Trends in dairy goats. J. Dairy Sci., 63: 1600-1604. LeJambre, L.F., 1984. Stocking rate effects on the worm burdens of Angora goats and Merino sheep. Aust. Vet. J., 61: 280-282. LeJambre, L.F. and Royal, W.M., 1976. A comparison of worm burdens in grazing Merino sheep and Angora goats. Aust. Vet. J., 52:181-183. Lutu, W.Z., 1983. Internal parasitism in milk goats in Kenya. Trop. Anim. Health Prod., 16: 153-157. McKenna, P.B., 1984. Gastro-intestinal parasitism and "anthelmintic resistance" in goats. Surveillance, 1 t: 2-4. McKenna, P.B. and Watson, T.G., 1987. The comparative efficacy of four broad spectrum anthelmintics against some experimentally induced trichostrongylid infections in sheep and goats. N.Z. Vet. J., 35: 192-195. Miller, A.J., 1991. Bleatings: Report from ADGA office. Dairy Goat J., 69 (3): 5. Njanja, J.C., Wescott, R.B. and Ruvuna, F., 1987. Comparison ofivermectin and thiabendazole for treatment of naturally occurring nematode infections of goats in Kenya. Vet. Parasitol., 23: 205-209. Pearson, A.B. and Rutherford, D.M., 1988. Ivermectin injection less effective in goats than oral treatment. Surveillance, 15: 22. Swan, G.E. and Gross, S.J., 1985. Efficacy of ivermectin against induced gastrointestinal nematode infections in goats. Vet. Rec., 117:147-149. Van Wyk, J.A. and Malan, F.S., 1988. Resistance of field strains ofHaemonchus contortus to ivermectin, closantel, rafoxanide and the benzimidazoles in South Africa. Vet. Rec., 123: 226-228. Wescott, R.B. and LeaMaster, B.R., 1982. Efficacy ofivermectin against naturally acquired and experimentally induced nematode infections in sheep. Am. J. Vet. Res., 43 (3): 531-533.
