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Rotational grazing for control of gastrointestinal nematodes of goats in a wet tropical environment
veterinary parasitology ELSEVIER
Veterinary Parasitology 53 (1994) 109-116
Rotational grazing for control of gastrointestinal nematodes of goats in a wet tropical environment I.A. Barger *,a, K. Siale b, D.J.D. Banks c, L.F. Le
Jambre
a
aCSIRO Division of Animal Health, Private Bag, Arrnidale, N.S. W.. 2350, Australia bMinistry of Agriculture and Forestry, Nuku'alofa, Tonga CAustralian Quarantine and Inspection Service, GPO Box 858, Canberra, A. C. T. 2601, Australia (Accepted 11 August 1993)
Abstract
A preliminary experiment involving contamination of pasture plots with eggs of Haemonchus contortus, Trichostrongylus colubriformis and Oesophagostomum columbianum every month for a year established that in the tropical environment of the Pacific island of Tongatapu, hatching and development of all species was rapid and continuous, with a short survival on pasture (3-7 weeks) of the resulting infective larvae. These results indicated that a rotational grazing system consisting of ten paddocks grazed in sequence for 3.5 days at a time may permit a reduction in the frequency of anthelmintic treatment of goats. In comparison with an adjacent set-stocked flock which required treatment on three occasions during the year when mean flock egg counts exceeded 2000 eggs per gram (EPG), rotationally grazed goats generally maintained mean egg counts of less than 1000 EPG. Anthelmintic treatment was only given to rotationally grazed goats individually as they kidded, and there were indications that even this precaution was unnecessary. Because of the expense of frequent anthelmintic treatment and the resulting selection of strains of anthelmintic-resistant nematodes, rotational grazing of small ruminants through fencing, tethering or herding deserves further investigation as a nematode control option in wet tropical environments. Key words: Haemonchus contortus; Trichostrongylus colubriforrnis; Oesophagostornum columbianum; Goat; Grazing management
*Corresponding author. 0304-4017/94/$07.00 © 1994 Elsevier Science B.V. All fights reserved SSD10304-4017 ( 93 ) 00586-N
110
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1. Introduction
Several Pacific Island countries have attempted to increase production of small ruminants in order to reduce their reliance on imported sheep and goat meat. Under the wet tropical conditions of these islands, nematode parasites, chiefly Haemonchus contortus and Trichostrongylus colubriformis, cause heavy mortality and production losses on commercial goat farms (Hussain et al., 1983; Banks et al., 1990). Control using anthelmintics alone is expensive, requiring treatment every 3-4 weeks, and has rapidly resulted in widespread resistance to the small number of broad-spectrum anthelmintics currently available. Methods of controlling gastrointestinal nematode parasites that do not rely on frequent anthelmintic treatment are urgently required. Although climatic conditions permit nematode egg hatching and larval development throughout the year in the wet tropics, Banks et al. (1990) found that survival times of the resulting infective larvae on pasture in Fiji were much shorter ( 5-13 weeks) than the survival times of up to 12 months reported from temperate climates. Similar short survival times of infective larvae on pasture have been reported during the wet season in Nigeria (Okon and Enyenihi, 1977; Fakae and Chiejina, 1988), Guadeloupe (Aumont and Gruner, 1989) and north Queensland (Fabiyi et al., 1988). Aumont and Gruner (1989) and Banks et al. (1990) suggested that the short survival times of infective larvae may make control through rotational grazing practicable in tropical regions. Such methods have not been successful in temperate climates because the time needed to ensure a significant reduction in larval numbers through spelling of pastures is agronomically and economically unacceptable (Donald, 1968; Southcott, 1971; Gibson, 1973 ). There were two aims of the present study: to see whether the pattern of rapid egg hatching and larval development, allied with short survival of larvae on pasture, observed by Banks et al. (1990) in Fiji could also be demonstrated in the cooler climate of Tonga, and if so, whether this could be exploited for parasite control through rotational grazing.
2. Materials and methods
2.1. Site The island of Tongatapu (21 ° 10' S, 175 ° 10'W) in Tonga has an mean annual rainfall of around 1800 mm. Rain can be expected in any month of the year, but there is a well-defined wet season from October to May. Mean monthly maxim u m air temperatures range from 24 ° C in August to 30 ° C in January, with mean monthly minima in the same months of 16°C and 20°C, respectively. Experimental plots were situated at the Ministry of Agriculture and Forestry Experimental Farm at Vaini, about 8 km southeast of the capital, Nuku'alofa. Pastures consisted mainly of Guinea grass (Panicum maximum).
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2.2. Larval development and survival Thirteen plots, each 5 m × 2 m were laid out in March 1989 on pasture that had not been grazed by goats for the previous 6 months. Drainage ditches were dug between plots to avoid cross-contamination during heavy rain, and the array of plots was fenced to prevent the entry of animals. From April 1989 to March 1990, one plot was randomly selected and uniformly contaminated in the first week of each month with faeces from naturally infected goats. The weight of faeces used to contaminate each plot was calculated from the current faecal egg count of the donor goats to contain a total of one million eggs, with known proportions of Haemonchus, Trichostrongylus and Oesophagostomum as determined on each occasion by faecal culture. The thirteenth plot was not contaminated, but was sampled each month to detect any extraneous infection. Plots were sampled at weekly intervals after contamination by collecting 60 uniformly distributed plucks of herbage per plot taken at ground level. Infective larvae were recovered from these samples using the technique of Heath and Major (1968). Sampling was avoided within 1 day after heavy rain, and was continued until no larvae were recovered from 2 consecutive weekly samples. Plots were slashed when required to maintain a similar pasture height to that of an adjacent continuously grazed goat pasture; clippings remained on the plot.
2.3. Rotational grazing trial Preliminary experiments conducted in Fiji had shown that infective larvae of
H. contortus and T. colubriformis were first detected in faeces 4 days after egg deposition, thus defining the maximum period that goats could be allowed to graze a paddock without risk of immediate auto-infection. The findings of Banks et al. (1990) in Fiji, together with those of the present larval survival study, suggested that at least 90% of infective larvae had disappeared from pasture by 4-5 weeks after their first appearance following egg deposition. Accordingly, a tenpaddock rotational grazing system was devised in which each paddock was grazed for 3.5 days, then spelled for 31.5 days. A grazing period of 3.5 rather than 4 days was chosen so that stock movements were made at the same times on the same days of each week. Does were randomly allocated to two flocks of 20 animals for comparison over 1 year from October 1991 to October 1992. Each flock grazed an area of 3 ha. The set-stocked flock had access to the whole of their area every day, while the 3 ha available to the rotationally grazed flock was subdivided, using solar-powered electric fencing, into ten equal paddocks; the flock followed the rotation described above. Each flock was housed separately in slatted-floor sheds at night to prevent theft or dog attack. The areas used for the two flocks were adjacent, similar in soil and pasture cover and both had been regularly grazed by goats before the trial began. All goats in both flocks were treated with ivermectin on the first day of the trial, and again on Day 15, to avoid heavy contamination of their grazing areas for the first month of the trial and to minimise differences between the
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two areas attributable to pre-experimental contamination. Faecal samples were obtained from all goats for faecal egg counts and larval identification at 2 week intervals thereafter. The anthelmintic treatment programme for both flocks was based on the resuits of these 2-week egg counts. If the flock arithmetic mean egg count exceeded 2000 eggs per gram ( E P G ) at any sampling, then each animal in that flock was treated with ivermectin at a dose rate of 300/tg kg- 1 liveweight. Preliminary observations had established that this dose reduced egg counts to zero. In addition, goats in the rotationally grazed flock were individually treated with ivermectin immediately after kidding. Kidding occurred during December and September in both flocks, with approximately half of the does kidding at each time. Kids remained with their dams for the duration of the trial and received any anthelmintic treatments that their dams required. Faecal egg counts were transformed (logX+ 50) for statistical analysis, and counts from both flocks in Weeks 2, 4, 16, 18, 28, 30 and 38 were excluded from the analysis. These times followed anthelmintic treatment of one or both flocks, when most animals in the treated flock had zero counts, leading to abnormally low or zero within-flock variance. Statistical significance of the difference between flocks in egg counts was assessed by a multivariate repeated measures analysis (Wilkinson, 1990).
3. Results
3.1. Larval development and survival No infective, third-stage larvae (L3) w e r e recovered from the control plot on any sampling occasion. Third-stage larvae of Haemonchus, Trichostrongylus and Oesophagostomum were routinely recovered in the first week after plot contamination in any month of the year, with the longest period of recovery being 7 weeks in May, October and November. Concentrations on pasture of L 3 of the three genera, corrected for numbers of eggs used to contaminate the plots, are shown for each month in Fig. 1. All genera appeared to be remarkably similar in their ability to hatch, develop to L 3 and survive under Tongan conditions. Concentrations of L3 o n pasture tended to be higher during the warmer months from November to February, with survival curtailed to 3 or 4 weeks in December, January and February.
3.2. Rotational grazing trial Geometric mean faecal egg counts of the rotationally grazed and set-stocked flocks over the 52 weeks of the trial are shown in Fig. 2. Mean counts over the full period were higher in the set-stocked flock ( P < 0 . 0 0 1 ) and there was a significant time by flock interaction ( P = 0.001 ), indicating that the difference in egg count between flocks varied with time. The set-stocked flock required three
LA. Barger et al. / Veterinary Parasitology 53 (1994) 109-116
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Fig. 1. Pasture larval recoveries of infective larvae per kilogram pasture dry matter, corrected for numbers of eggs deposited, on plots contaminated sequentially from April 1989 to March 1990. Haem, Haemonchus contortus; Trich, Trichostrongylus colubriformis; Oesoph, Oesophagostomum
columbianum.
additional anthelmintic treatments when mean egg counts exceeded 2000 EPG; the times of these treatments are shown by the arrows in Fig. 1. Nine of the 20 goats in this flock also required single treatments in Weeks 42-50 for welfare reasons; these animals were losing condition and scouring. Rotationally grazed goats required no additional treatments beyond their planned treatment at kidding, and their mean egg count only exceeded 1000 EPG on one occasion (Week
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Fig. 2. Geometricmean faecal egg counts of set-stocked or rotationallygrazed goats from October 1991 to October 1992. Anthelmintictreatmentswere givento all goats in the set-stockedflockat the times indicatedby the arrows. Rotationallygrazed goats receivedone treatment each followingthe birth of kids. 28 ). A total of 69 doses of ivermectin was therefore administered to the 20 setstocked goats, compared with 20 doses administered to the rotationally grazed flock. Faecal cultures of composite samples from each flock every fortnight showed no consistent differences between flocks in generic composition of nematode egg output. H a e m o n c h u s and Trichostrongylus comprised 30-60% of larvae recovered from cultures, with Oesophagostomum ranging from 5 to 30%. Haernonchus tended to predominate from December to March, with Trichostrongylus more numerous from April to December. Two deaths occurred during the trial. One set-stocked doe was found dead in Week 36 at a time when that flock had very high egg counts; the cause of death was not established. One rotationally grazed doe died in Week 49 of injuries received from unknown causes. Autopsy revealed broken ribs and extensive bruising.
4. Discussion The results of the larval development and survival experiment confirm results obtained in the hotter climate of Fiji by Banks et al. (1990), and suggest that similar results would be obtained in other tropical and possibly sub-tropical regions provided that rainfall throughout the year was sufficient to allow development to L 3. The survival times observed in the present study, ranging from 3 to 7 weeks, were even shorter than those observed in Fiji, particularly during the cooler period from April to August. This may be attributable to the more evenly distributed rainfall in Tongatapu in 199 l-1992 in comparison with that in Koronivia and Sigatoka in 1986-1987, when the observations of Banks et al. (1990) were recorded. At both Fijian sites there was a marked dry season at that time, and there is evidence that dry weather enhances the survival of nematode L 3 in faeces
LA. Barger et al. / Veterinary Parasitology 53 (1994) 109-116
115
by limiting their opportunities to migrate to pasture, where death rates are higher (Barger et al., 1984). The results of the rotational grazing trial, while encouraging, must be regarded with caution. Because the experiment was not replicated, it was not possible to reach a firm conclusion about the cause of the lower egg counts in the rotationally grazed flock. While we believe that they were a result of the rotation of paddocks at 3.5 day intervals, the lack of replication means that differences between the grazing areas occupied by the two flocks cannot be excluded as an explanation. However, both areas carried a similar pasture cover at the beginning of the experiment, were adjacent and had a similar prior grazing history with goats. In addition, the two ivermectin treatments given to all goats on Days 1 and 15 of the trial meant that neither area was contaminated with nematode eggs for a period of around 5 weeks at the beginning of the trial, by which time residual larval populations must have declined to very low levels. Individual anthelmintic treatment of rotationally grazed does following parturition was instituted because of concern about the possible loss of acquired immunity of periparturient does to nematode infection. This phenomenon is wellknown in ewes (Connan, 1976 ) but there was no indication in the present study in either the set-stocked or rotationally grazed does that unusually elevated egg counts were associated with parturition or lactation. Rahman and Collins ( 1992 ) recently published evidence of a periparturient rise in faecal egg counts in goats; in contrast to sheep the rise was mild and reached a peak several weeks before parturition followed by a decline through lactation. The lower egg counts of the rotationally grazed goats are consistent with results of the larval survival experiment, and with unpublished observations by D.J.D. Banks ( 1988 ) in Fiji that nematode parasitism was rarely a problem in traditionally managed village goats, despite the lack of anthelmintic treatment. Under traditional management, goats were tethered and moved to a new grazing area every 1 or 2 days. Fencing of rotationaUy grazed pastures, as practised in the present study, is therefore not essential, although subdivisional electric fencing is less expensive than traditional permanent perimeter fencing. Management systems employing goatherds to move the flock to new grazing areas every few days should be equally successful provided that the flock does not return to any area within 4 or 5 weeks of its last grazing. Rotational grazing systems for small ruminants in wet tropical climates, whether implemented through fencing, tethering or herding, therefore warrant further investigation as a low-cost means of reducing reliance on anthelmintics.
5. Acknowledgements We gratefully acknowledge the assistance and co-operation of Aleki Sisifa, Director of Agriculture, and the Ministry of Agriculture and Forestry in Tonga, who provided staff and facilities for this study. We also thank the Australian Centre for International Agricultural Research for generous financial support.
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References Aumont, G. and Gruner, L., 1989. Population evolution of the free-living stage of goat gastrointestinal nematodes on herbage under tropical conditions in Guadeloupe (French West Indies). Int. J. Parasitol., 19: 539-546. Banks, D.J.D., Singh, R., Barger, I.A., Pratap, B. and Le Jambre, L.F., 1990. Development and survival of infective larvae of Haemonchus contortus and Trichostrongylus colubriformis in a tropical environment. Int. J. Parasitol., 20:155-160. Barger, I.A., Lewis, R.J. and Brown, G.F., 1984. Survival of infective larvae of nematode parasites of cattle during drought. Vet. Parasitol., 14:143-152. Connan, R.M., 1976. Effect of lactation on the immune response to gastrointestinal nematodes. Vet. Rec., 99: 476-477. Donald, A.D., 1968. Ecology of the free-living stages of nematode parasites of sheep. Aust. Vet. J., 44: 139-144.
Fabiyi, J.P., Copeman, D.B. and Hutchinson, G.W., 1988. Abundance and survival of infective larvae of the cattle nematodes Cooperia punctata, Haemonchus placei, and Oesophagostomum radiatum from faecal pats in a wet tropical climate. Aust. Vet. J., 65:229-231. Fakae, B.B. and Chiejina, S.N., 1988. Further studies on the development and availability of infective larvae of bovine gastrointestinal trichostrongylids on pasture in Eastern Nigeria. Vet. Parasitol., 28: 143-152. Gibson, T.E., 1973. Recent advances in the epidemiology and control of parasitic gastroenteritis in sheep. Vet. Rec., 92: 469-473. Heath, D.D. and Major, G.W., 1968. A technique for the recovery of strongyle larvae from masticated herbage. J. Helminthol., 42: 299-304. Hussain, M.Z., Naidu, R., Tuvuki, I. and Singh, R., 1983. Goat production and development in Fiji. World Anim. Rev., 48: 25-32. Okon, D.E. and Enyenihi, U.K., 1977. Development and survival ofHaemonchus contortus larvae on pastures in Ibadan. Trop. Anita. Health Prod., 9: 7-10. Rahman, W.A. and Collins, G.H., 1992. An association of faecal egg counts and prolactin concentrations in sera of periparturient Angora goats. Vet. Parasitol., 43:85-91. Southcott, W.H., 1971. Management practices and helminthosis in the lamb. Aust. Vet. J., 47: 170174. Wilkinson, L., 1990. SYSTAT: The System for Statistics. SYSTAT, Evanston, IL, 677 pp.
Veterinary Parasitology 53 (1994) 109-116
Rotational grazing for control of gastrointestinal nematodes of goats in a wet tropical environment I.A. Barger *,a, K. Siale b, D.J.D. Banks c, L.F. Le
Jambre
a
aCSIRO Division of Animal Health, Private Bag, Arrnidale, N.S. W.. 2350, Australia bMinistry of Agriculture and Forestry, Nuku'alofa, Tonga CAustralian Quarantine and Inspection Service, GPO Box 858, Canberra, A. C. T. 2601, Australia (Accepted 11 August 1993)
Abstract
A preliminary experiment involving contamination of pasture plots with eggs of Haemonchus contortus, Trichostrongylus colubriformis and Oesophagostomum columbianum every month for a year established that in the tropical environment of the Pacific island of Tongatapu, hatching and development of all species was rapid and continuous, with a short survival on pasture (3-7 weeks) of the resulting infective larvae. These results indicated that a rotational grazing system consisting of ten paddocks grazed in sequence for 3.5 days at a time may permit a reduction in the frequency of anthelmintic treatment of goats. In comparison with an adjacent set-stocked flock which required treatment on three occasions during the year when mean flock egg counts exceeded 2000 eggs per gram (EPG), rotationally grazed goats generally maintained mean egg counts of less than 1000 EPG. Anthelmintic treatment was only given to rotationally grazed goats individually as they kidded, and there were indications that even this precaution was unnecessary. Because of the expense of frequent anthelmintic treatment and the resulting selection of strains of anthelmintic-resistant nematodes, rotational grazing of small ruminants through fencing, tethering or herding deserves further investigation as a nematode control option in wet tropical environments. Key words: Haemonchus contortus; Trichostrongylus colubriforrnis; Oesophagostornum columbianum; Goat; Grazing management
*Corresponding author. 0304-4017/94/$07.00 © 1994 Elsevier Science B.V. All fights reserved SSD10304-4017 ( 93 ) 00586-N
110
LA. Barger et al. / Veterinary Parasitology 53 (1994) 109-116
1. Introduction
Several Pacific Island countries have attempted to increase production of small ruminants in order to reduce their reliance on imported sheep and goat meat. Under the wet tropical conditions of these islands, nematode parasites, chiefly Haemonchus contortus and Trichostrongylus colubriformis, cause heavy mortality and production losses on commercial goat farms (Hussain et al., 1983; Banks et al., 1990). Control using anthelmintics alone is expensive, requiring treatment every 3-4 weeks, and has rapidly resulted in widespread resistance to the small number of broad-spectrum anthelmintics currently available. Methods of controlling gastrointestinal nematode parasites that do not rely on frequent anthelmintic treatment are urgently required. Although climatic conditions permit nematode egg hatching and larval development throughout the year in the wet tropics, Banks et al. (1990) found that survival times of the resulting infective larvae on pasture in Fiji were much shorter ( 5-13 weeks) than the survival times of up to 12 months reported from temperate climates. Similar short survival times of infective larvae on pasture have been reported during the wet season in Nigeria (Okon and Enyenihi, 1977; Fakae and Chiejina, 1988), Guadeloupe (Aumont and Gruner, 1989) and north Queensland (Fabiyi et al., 1988). Aumont and Gruner (1989) and Banks et al. (1990) suggested that the short survival times of infective larvae may make control through rotational grazing practicable in tropical regions. Such methods have not been successful in temperate climates because the time needed to ensure a significant reduction in larval numbers through spelling of pastures is agronomically and economically unacceptable (Donald, 1968; Southcott, 1971; Gibson, 1973 ). There were two aims of the present study: to see whether the pattern of rapid egg hatching and larval development, allied with short survival of larvae on pasture, observed by Banks et al. (1990) in Fiji could also be demonstrated in the cooler climate of Tonga, and if so, whether this could be exploited for parasite control through rotational grazing.
2. Materials and methods
2.1. Site The island of Tongatapu (21 ° 10' S, 175 ° 10'W) in Tonga has an mean annual rainfall of around 1800 mm. Rain can be expected in any month of the year, but there is a well-defined wet season from October to May. Mean monthly maxim u m air temperatures range from 24 ° C in August to 30 ° C in January, with mean monthly minima in the same months of 16°C and 20°C, respectively. Experimental plots were situated at the Ministry of Agriculture and Forestry Experimental Farm at Vaini, about 8 km southeast of the capital, Nuku'alofa. Pastures consisted mainly of Guinea grass (Panicum maximum).
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2.2. Larval development and survival Thirteen plots, each 5 m × 2 m were laid out in March 1989 on pasture that had not been grazed by goats for the previous 6 months. Drainage ditches were dug between plots to avoid cross-contamination during heavy rain, and the array of plots was fenced to prevent the entry of animals. From April 1989 to March 1990, one plot was randomly selected and uniformly contaminated in the first week of each month with faeces from naturally infected goats. The weight of faeces used to contaminate each plot was calculated from the current faecal egg count of the donor goats to contain a total of one million eggs, with known proportions of Haemonchus, Trichostrongylus and Oesophagostomum as determined on each occasion by faecal culture. The thirteenth plot was not contaminated, but was sampled each month to detect any extraneous infection. Plots were sampled at weekly intervals after contamination by collecting 60 uniformly distributed plucks of herbage per plot taken at ground level. Infective larvae were recovered from these samples using the technique of Heath and Major (1968). Sampling was avoided within 1 day after heavy rain, and was continued until no larvae were recovered from 2 consecutive weekly samples. Plots were slashed when required to maintain a similar pasture height to that of an adjacent continuously grazed goat pasture; clippings remained on the plot.
2.3. Rotational grazing trial Preliminary experiments conducted in Fiji had shown that infective larvae of
H. contortus and T. colubriformis were first detected in faeces 4 days after egg deposition, thus defining the maximum period that goats could be allowed to graze a paddock without risk of immediate auto-infection. The findings of Banks et al. (1990) in Fiji, together with those of the present larval survival study, suggested that at least 90% of infective larvae had disappeared from pasture by 4-5 weeks after their first appearance following egg deposition. Accordingly, a tenpaddock rotational grazing system was devised in which each paddock was grazed for 3.5 days, then spelled for 31.5 days. A grazing period of 3.5 rather than 4 days was chosen so that stock movements were made at the same times on the same days of each week. Does were randomly allocated to two flocks of 20 animals for comparison over 1 year from October 1991 to October 1992. Each flock grazed an area of 3 ha. The set-stocked flock had access to the whole of their area every day, while the 3 ha available to the rotationally grazed flock was subdivided, using solar-powered electric fencing, into ten equal paddocks; the flock followed the rotation described above. Each flock was housed separately in slatted-floor sheds at night to prevent theft or dog attack. The areas used for the two flocks were adjacent, similar in soil and pasture cover and both had been regularly grazed by goats before the trial began. All goats in both flocks were treated with ivermectin on the first day of the trial, and again on Day 15, to avoid heavy contamination of their grazing areas for the first month of the trial and to minimise differences between the
112
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two areas attributable to pre-experimental contamination. Faecal samples were obtained from all goats for faecal egg counts and larval identification at 2 week intervals thereafter. The anthelmintic treatment programme for both flocks was based on the resuits of these 2-week egg counts. If the flock arithmetic mean egg count exceeded 2000 eggs per gram ( E P G ) at any sampling, then each animal in that flock was treated with ivermectin at a dose rate of 300/tg kg- 1 liveweight. Preliminary observations had established that this dose reduced egg counts to zero. In addition, goats in the rotationally grazed flock were individually treated with ivermectin immediately after kidding. Kidding occurred during December and September in both flocks, with approximately half of the does kidding at each time. Kids remained with their dams for the duration of the trial and received any anthelmintic treatments that their dams required. Faecal egg counts were transformed (logX+ 50) for statistical analysis, and counts from both flocks in Weeks 2, 4, 16, 18, 28, 30 and 38 were excluded from the analysis. These times followed anthelmintic treatment of one or both flocks, when most animals in the treated flock had zero counts, leading to abnormally low or zero within-flock variance. Statistical significance of the difference between flocks in egg counts was assessed by a multivariate repeated measures analysis (Wilkinson, 1990).
3. Results
3.1. Larval development and survival No infective, third-stage larvae (L3) w e r e recovered from the control plot on any sampling occasion. Third-stage larvae of Haemonchus, Trichostrongylus and Oesophagostomum were routinely recovered in the first week after plot contamination in any month of the year, with the longest period of recovery being 7 weeks in May, October and November. Concentrations on pasture of L 3 of the three genera, corrected for numbers of eggs used to contaminate the plots, are shown for each month in Fig. 1. All genera appeared to be remarkably similar in their ability to hatch, develop to L 3 and survive under Tongan conditions. Concentrations of L3 o n pasture tended to be higher during the warmer months from November to February, with survival curtailed to 3 or 4 weeks in December, January and February.
3.2. Rotational grazing trial Geometric mean faecal egg counts of the rotationally grazed and set-stocked flocks over the 52 weeks of the trial are shown in Fig. 2. Mean counts over the full period were higher in the set-stocked flock ( P < 0 . 0 0 1 ) and there was a significant time by flock interaction ( P = 0.001 ), indicating that the difference in egg count between flocks varied with time. The set-stocked flock required three
LA. Barger et al. / Veterinary Parasitology 53 (1994) 109-116
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Fig. 1. Pasture larval recoveries of infective larvae per kilogram pasture dry matter, corrected for numbers of eggs deposited, on plots contaminated sequentially from April 1989 to March 1990. Haem, Haemonchus contortus; Trich, Trichostrongylus colubriformis; Oesoph, Oesophagostomum
columbianum.
additional anthelmintic treatments when mean egg counts exceeded 2000 EPG; the times of these treatments are shown by the arrows in Fig. 1. Nine of the 20 goats in this flock also required single treatments in Weeks 42-50 for welfare reasons; these animals were losing condition and scouring. Rotationally grazed goats required no additional treatments beyond their planned treatment at kidding, and their mean egg count only exceeded 1000 EPG on one occasion (Week
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-
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E~ ~.c ~v
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o
0
4
8
12
16
20
24
Weeks lira S e t - s t o c k e d ~
28
32
36
40
44
48
52
Rotation
Fig. 2. Geometricmean faecal egg counts of set-stocked or rotationallygrazed goats from October 1991 to October 1992. Anthelmintictreatmentswere givento all goats in the set-stockedflockat the times indicatedby the arrows. Rotationallygrazed goats receivedone treatment each followingthe birth of kids. 28 ). A total of 69 doses of ivermectin was therefore administered to the 20 setstocked goats, compared with 20 doses administered to the rotationally grazed flock. Faecal cultures of composite samples from each flock every fortnight showed no consistent differences between flocks in generic composition of nematode egg output. H a e m o n c h u s and Trichostrongylus comprised 30-60% of larvae recovered from cultures, with Oesophagostomum ranging from 5 to 30%. Haernonchus tended to predominate from December to March, with Trichostrongylus more numerous from April to December. Two deaths occurred during the trial. One set-stocked doe was found dead in Week 36 at a time when that flock had very high egg counts; the cause of death was not established. One rotationally grazed doe died in Week 49 of injuries received from unknown causes. Autopsy revealed broken ribs and extensive bruising.
4. Discussion The results of the larval development and survival experiment confirm results obtained in the hotter climate of Fiji by Banks et al. (1990), and suggest that similar results would be obtained in other tropical and possibly sub-tropical regions provided that rainfall throughout the year was sufficient to allow development to L 3. The survival times observed in the present study, ranging from 3 to 7 weeks, were even shorter than those observed in Fiji, particularly during the cooler period from April to August. This may be attributable to the more evenly distributed rainfall in Tongatapu in 199 l-1992 in comparison with that in Koronivia and Sigatoka in 1986-1987, when the observations of Banks et al. (1990) were recorded. At both Fijian sites there was a marked dry season at that time, and there is evidence that dry weather enhances the survival of nematode L 3 in faeces
LA. Barger et al. / Veterinary Parasitology 53 (1994) 109-116
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by limiting their opportunities to migrate to pasture, where death rates are higher (Barger et al., 1984). The results of the rotational grazing trial, while encouraging, must be regarded with caution. Because the experiment was not replicated, it was not possible to reach a firm conclusion about the cause of the lower egg counts in the rotationally grazed flock. While we believe that they were a result of the rotation of paddocks at 3.5 day intervals, the lack of replication means that differences between the grazing areas occupied by the two flocks cannot be excluded as an explanation. However, both areas carried a similar pasture cover at the beginning of the experiment, were adjacent and had a similar prior grazing history with goats. In addition, the two ivermectin treatments given to all goats on Days 1 and 15 of the trial meant that neither area was contaminated with nematode eggs for a period of around 5 weeks at the beginning of the trial, by which time residual larval populations must have declined to very low levels. Individual anthelmintic treatment of rotationally grazed does following parturition was instituted because of concern about the possible loss of acquired immunity of periparturient does to nematode infection. This phenomenon is wellknown in ewes (Connan, 1976 ) but there was no indication in the present study in either the set-stocked or rotationally grazed does that unusually elevated egg counts were associated with parturition or lactation. Rahman and Collins ( 1992 ) recently published evidence of a periparturient rise in faecal egg counts in goats; in contrast to sheep the rise was mild and reached a peak several weeks before parturition followed by a decline through lactation. The lower egg counts of the rotationally grazed goats are consistent with results of the larval survival experiment, and with unpublished observations by D.J.D. Banks ( 1988 ) in Fiji that nematode parasitism was rarely a problem in traditionally managed village goats, despite the lack of anthelmintic treatment. Under traditional management, goats were tethered and moved to a new grazing area every 1 or 2 days. Fencing of rotationaUy grazed pastures, as practised in the present study, is therefore not essential, although subdivisional electric fencing is less expensive than traditional permanent perimeter fencing. Management systems employing goatherds to move the flock to new grazing areas every few days should be equally successful provided that the flock does not return to any area within 4 or 5 weeks of its last grazing. Rotational grazing systems for small ruminants in wet tropical climates, whether implemented through fencing, tethering or herding, therefore warrant further investigation as a low-cost means of reducing reliance on anthelmintics.
5. Acknowledgements We gratefully acknowledge the assistance and co-operation of Aleki Sisifa, Director of Agriculture, and the Ministry of Agriculture and Forestry in Tonga, who provided staff and facilities for this study. We also thank the Australian Centre for International Agricultural Research for generous financial support.
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Fabiyi, J.P., Copeman, D.B. and Hutchinson, G.W., 1988. Abundance and survival of infective larvae of the cattle nematodes Cooperia punctata, Haemonchus placei, and Oesophagostomum radiatum from faecal pats in a wet tropical climate. Aust. Vet. J., 65:229-231. Fakae, B.B. and Chiejina, S.N., 1988. Further studies on the development and availability of infective larvae of bovine gastrointestinal trichostrongylids on pasture in Eastern Nigeria. Vet. Parasitol., 28: 143-152. Gibson, T.E., 1973. Recent advances in the epidemiology and control of parasitic gastroenteritis in sheep. Vet. Rec., 92: 469-473. Heath, D.D. and Major, G.W., 1968. A technique for the recovery of strongyle larvae from masticated herbage. J. Helminthol., 42: 299-304. Hussain, M.Z., Naidu, R., Tuvuki, I. and Singh, R., 1983. Goat production and development in Fiji. World Anim. Rev., 48: 25-32. Okon, D.E. and Enyenihi, U.K., 1977. Development and survival ofHaemonchus contortus larvae on pastures in Ibadan. Trop. Anita. Health Prod., 9: 7-10. Rahman, W.A. and Collins, G.H., 1992. An association of faecal egg counts and prolactin concentrations in sera of periparturient Angora goats. Vet. Parasitol., 43:85-91. Southcott, W.H., 1971. Management practices and helminthosis in the lamb. Aust. Vet. J., 47: 170174. Wilkinson, L., 1990. SYSTAT: The System for Statistics. SYSTAT, Evanston, IL, 677 pp.