Relative contributions of late dry-season and early rains pasture contaminations with trichostrongyle eggs to the wet-season herbage infestation in eastern Nigeria

Two worm-free grass paddocks, P1 and P2, were artificially contaminated in March and April-May, respectively, with bovine faeces containing known numbers of trichostrongyle (mainly Cooperia, Haemonchus and Trichostrongylus spp.) eggs in order to determine the relative contributions of late dry-season and early rains pasture contaminations to the wet-season herbage larval infestation in Nsukka, eastern Nigeria. The resulting herbage infestation was assessed by means of larval counts and tracer studies. A sudden rise in herbage infestation occurred simultaneously in both paddocks in late April, this apparently being determined by the onset of the first substantial rainfall of the wet season. Peak infestations in both paddocks also occurred simultaneously in May. The infestation in P1 was much larger, and the larval population persisted longer, than that in P2 and later gave rise to a second smaller peak in June. No L3 were recovered in herbage samples from either of the paddocks after the third week of July. Both paddocks were infective to goats in May-June, while P2 was also infective in July-August. The results suggest that in the Nigerian derived savanna the initial wet-season herbage infestation in pastures grazed by infected cattle during the dry and wet seasons will consist of L3 from late dry-season and early rains pasture contaminations, the former being the major contributor to the infestation. Consequently, pastures contaminated during the late dry season may not be safe for susceptible animals to graze at the start of the succeeding rainy season.     

Further studies on the development and availability of infective larvae of bovine gastrointestinal trichostrongylids on pasture in eastern Nigeria

The dynamics of pasture populations of infective larvae (L3) of Cooperia, Haemonchus and Trichostrongylus species were studied at Nsukka, eastern Nigeria, during April to November 1984. Six paddocks were contaminated artificially and one was contaminated naturally. Five of the paddocks, P1-P5, were sequentially contaminated with faeces of naturally infected cattle at approximately 4-6-weekly intervals. Paddocks P6 and P7 were repeatedly contaminated every 4-6 weeks artificially and by the naturally infected cattle, respectively. Larval development and survival occurred very readily during the wet season (April-October) but apparently ceased in November at the start of the dry season. Larval migration, however, occurred not only during the rains but also during the first 4 weeks of the dry season. Single contaminations during the rains quickly gave rise to single waves of infestation which also declined rapidly, in spite of the continuously favourable conditions for larval development and survival. The repeated contaminations produced three and four distinct and relatively short-lived larval peaks, respectively, with the first three peaks on both paddocks, namely the May, July and September/October peaks, being coincident. The four waves of herbage infestation on P7, which occurred at approximately 4-5 weekly intervals, were considered to have originated from four separate generations of the three trichostrongylids. However, Trichostrongylus sp. predominated in the first (May) peak while Cooperia and Haemonchus dominated the later peaks.     

Development and survival of infective larvae of gastrointestinal nematode parasites of cattle on pasture in eastern Nigeria

A study of the development and survival of the infective larvae of the common strongylate nematodes of cattle at Nsukka, eastern Nigeria, from September 1981 to March 1982 showed that the dry season (November to March) was generally unfavourable for preparasitic development and survival of Cooperia, Haemonchus and Trichostrongylus species. However significant development may occur during the last two months of the season as a result of the small amounts of rain that usually fall at that time of the year. It was shown, using tracer goat kids, that only paddocks contaminated late in the dry season were infective at the start of the rainy season and that March contamination, in particular, is an important source of the 'early rains' (April/May) rise in herbage infestation commonly observed.     

Development,Survival and Availability of Gastrointestinal Nematodes of Sheep and Pastures in a Semi-arid Area of Kajiado District of Kenya

A study was carried out on a ranch in the semi-arid area of Kajiado District in Kenya during the period July 2000 to June 2001 to determine the seasonal patterns of development and survival of gastrointestinal nematodes of sheep on pastures. A series of plots were contaminated with sheep faeces every month and pasture samples were collected weekly for the recovery and identification of larvae. The availability of infective larvae on naturally contaminated pastures was also monitored on the paddocks grazed by sheep and around the night pen and the watering point every month from July 2000 to June 2001. The results from the examination of the pasture samples indicated that rainfall distribution was the major factor governing the development and survival of the pre-parasitic stages. No parasitic larvae were detected from the plots contaminated during the dry months from July to October 2000, but development and translocation of infective larvae on pastures occurred on plots contaminated during the rainy seasons and soon after when relatively high moisture was present in the herbage (November 2000 to June 2001). During this period, peak larval counts occurred between the first and the second week post contamination, then declined to undetectable levels between week 4 and 16 post contamination. The lack of development of infective larvae during the dry season and the relatively rapid decline of their population during the wet season presents an opportunity for the use of pasture spelling as a means of helminth control in the study area. The availability of infective larvae on naturally contaminated pastures, around the night pen and around the watering point also followed the rainfall distribution pattern. Infective larvae were consistently recovered around the watering point throughout the study period. This indicated that the point is an important source of infection for sheep, especially during the dry season when other pastures are non-infective.     

Population dynamics of the free-living stages of Amblyomma cajennense (Fabricius, 1787) (Acari: ixodidae) on pastures of Pedro Leopoldo, Minas Gerais State, Brazil

A study on the population behavior of Amblyomma cajennense larvae, nymphs and adult free-living stages was carried out in Pedro Leopoldo County, Minas Gerais State, Brazil, from July 1995 to July 1997. Larvae were collected from pasture from April to October using the technique of drag sampling with flannelette. The maximal larval population was observed during autumn (May) representing, respectively, 48 and 82% of the total numbers recovered during the first and the second years of the experiment. Nymphs and adults were captured throughout the year by the use of traps with carbon dioxide as chemical attractant. The highest population of nymphs occurred during the winter (July), representing 39.5% of the total collected specimens. Adults had the highest population density on pasture during spring and summer, i.e., from August to May, with peaks in January and February, representing 46 and 38.3% of the total collected specimens during the first and the second year of study, respectively.     

Epidemiology of Fasciola hepatica infection in the Paraíba River Valley, S?o Paulo, Brasil

The study revealed that although Lymnaea columella and Stenophysa marmorata were found in the same habitat, only L. columella harbored intramolluscan stages of F. hepatica. The population density of L. columella cyclically decreased between September and February, and increased from March to September. The drought that occurred between June and November 1981 dramatically reduced the number of snails collected. Larger snails were collected in March-July and November-December, while the smaller snails were collected in January-February and August-October, suggesting that there may be two generations of L. columella per year. The highest prevalence levels of infection in L. columella were: first year, June 8.82%, September 9.09% and October 10.52%; second year, March 6.25% and April 6.89%; third year, July 7.69%, August 10.25%, April 17.91% and May 13.91%. Results obtained with tracer sheep showed that the largest numbers of metacercariae were on pasture between June and October, and between March and April, but the infection was present during most of the year.     

Bovine fasciolosis in Tabasco, Mexico

To establish seasonal trends in infection and maturity of Fasciola hepatica in cattle in relation to macroclimatic factors, 2730 condemned livers were examined from March 1989 to February 1992. Livestock came from Jalapa, Tacotalpa and Teapa, all municipalities in Tabasco State. Flukes were collected monthly and separated into three different maturation stages. Mean numbers of flukes collected were determined. The analysis of the maturation stages detected in cattle showed: (a) F. hepatica matured throughout the year at all three sites; (b) the greatest mean fluke's burdens were found in Jalapa and the lowest in Teapa; large parasite populations were significantly higher from February to September than in July and/or August; (c) persistence of mature, gravid F. hepatica indicated that parasite eggs are shed throughout the year; (d) recruitment of F. hepatica occurred throughout the year with two major periods of infection, the first and main period during the dry season (from February to June), and a second minor infection period, during the rainy season (from August to October); (e) a close relationship was observed between the seasonal infection pattern in cattle and the seasonal infection pattern in snails, as well as fluctuations in the snail population according to rainfall and temperature variation.     

Physiological and parasitological responses to nematode infections of fattening cattle in the Western Pampas of Argentina

The epidemiology of nematode infection was studied in fattening grazing cattle from weaning (April 1994) to market at the end of their second autumn (July 1995). Sixty Aberdeen Angus calves of seven months of age were randomly allocated by weight to two groups: GT, treated every three weeks with doramectin (200 mcg/kg); and GI, an infected group, only treated with fenbendazole (7.5 mg/kg) at weaning and on the 1st of October. The two groups were grazed together on contaminated lucerne pastures until July, on 'clean' oat pastures until October and again on contaminated lucerne until the end of the trial. Fecal egg counts (epg), herbage larvae (L3), serum pepsinogen (Pep) and blood eosinophils (Eo) were evaluated monthly. Eight steers were slaughtered for worm recovery, three in July 1994, three in December 1994 and two in July 1995. Grazing feed intake was estimated by fecal output (chromic oxide method)/l-diet digestibility and to measure non-specific response, Brucella antibodies were detected at 11 and 40 days post-vaccination in early winter. Fecal egg counts, Pep and Eo of GI increased (P<0.01) from April to July when there was a moderate-to-high level of infection. Ostertagia, Trichostrongylus and Cooperia were the predominant genera. By late winter, all parameters decreased on oat 'clean' pastures and increased again when cattle returned to moderately infected lucerne. During summer, the parameters measured reflected the negligible numbers of L3 on pastures until early autumn. At this time, increased numbers of L3 were followed by a moderate rise (P<0.01) of epg, Pep and Eo values. During winter, GT showed higher (P<0.04) Brucella antibody IgG titers while feed intake of GI was 24.9% depressed (P<0.02). There were total cumulative weight-gain (WG) differences (P<0.001) between groups (GT=263.1 kg; GI=214.3 kg). During the second autumn, the mean WG of GT steers was 16.6 kg greater (P<0.04) than that of GI. Vaccination titres against Brucella suggested non-specific depression of immunity, while higher Pep and Eo levels in second-year steers may have reflected hypersensitivity reactions.     

亚高山草甸不同坡向牧草产量动态的研究

本文就山西亚高山草甸不同坡向牧草产量动态进行研究。三年定位研究结果表明，亚高山草甸牧草一般在四月中、下旬开始返青，随着气温的升高生长逐渐加快，牧草产量逐月增高，各坡向产草量动态均呈现单峰曲线变化规律。干草产量的峰值，东坡和西坡在七月，其它被向则出现在八月。九月上旬牧草开始枯萎，产草量开始下降，一直持续到翌年四月上旬牧草返青之前。牧草营养物质的变化，在生长前期粗蛋白质和磷含量高，随着牧草的生长发育逐渐减少，而粗纤维含量则相反。粗蛋白质产量高峰期，东、南和西坡在七月，北坡和山顶部在八月，与干草产量的高峰期基本吻合，此时正是牧草利用的最佳时期。除五、六月外其它各月青草期牧草产量和营养物质产量，北坡均显著高于其它各坡向（P＜0．05）。     

Development and survival of Haemonchus contortus isolated from sheep on a pasture at Bunia (Itiri, Zaire)]

Development and survival of Haemonchus contortus larvae were studied from December 1987 to November 1988 during three different periods (dry season, first and second rainy seasons) on an experimentally infected pasture at Bunia (Ituri, Za?re). Whatever the season, eggs developed into infective larvae within six days and the largest number of larvae on the herbage occurred between the 12th and the 18th day post deposition. However, the two rainy seasons were the most favourable for transmission because of the high number of larvae on the pasture and the increased survival of these larvae after 4 weeks.     

Development and survival of Haemonchus contortus larvae on pasture at Vom,Plateau State,Nigeria

The development and survival of the eggs of Haemonchus contortus on pasture at Vom were studied by depositing faecal pellets on grass plots over a period of 12 months. Development and survival to the infective larvae occurred throughout the study except during the dry season months of December to April. More infective larvae were recovered from the herbage in June, July and August than in other months. The survival time of the infective larvae ranged from 2 weeks in October to 10 weeks in June, July and August. Rainfall was the most important epizootiological factor influencing the development and survival of the infective larvae. Temperature was not a limiting factor.     

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

Observations were made on the abundance and survival of Haemonchus placei, Cooperia punctata and Oesophagostomum radiatum infective larvae from cattle faecal pats exposed at various times of the year in north Queensland wet tropics. Pats exposed in the hot, wet season yielded abundant larvae on herbage. In the dry season, although low numbers of infective larvae were usual, considerable numbers were produced under conditions of heavy dews on dense herbage. Irrespective of season of deposition of pats, the resulting larvae persisted generally for not longer than 10 to 12 weeks, and in large numbers for only 2 to 6 weeks. The findings suggest that prevention of contamination in the wet season, and in the dry season when light rainfalls are accompanied by heavy dews on dense herbage, will result in low levels of larval infestation on herbage. Rotational grazing in the area is suggested as a means of worm control.     

Epidemiological studies of Fasciola gigantica infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

During the period between January 1999 and December 2000, the distribution and seasonal patterns of Fasciola gigantica infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Cattle faecal samples were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas respectively. Patterns of distribution and seasonal fluctuations of the intermediate host-snail populations and the climatic factors influencing the distribution were also determined by sampling at monthly intervals for a period of 24 months (November 1998 to October 2000) in six dams and six streams in the highveld and in nine dams in the lowveld communal grazing areas. Each site was sampled for relative snail density and the vegetation cover and type, physical and chemical properties of water, and mean monthly rainfall and temperature were recorded. Aquatic vegetation and grass samples 0-1 m from the edges of the snail habitats were collected monthly to determine the presence or absence of F. gigantica metacercariae. Snails collected at the same time were individually checked for the emergence of larval stages of F. gigantica. A total of 16264 (calves 5418; weaners 5461 and adults 5385) faecal samples were collected during the entire period of the study and 2500 (15.4%) of the samples were positive for F. gigantica eggs. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), for adult cattle than calves (P < 0.01) and in the wet season over the dry season (P < 0.01). Faecal egg output peaked from August/September to March/April for both years of the study. Lymnaea natalensis, the snail intermediate host of F. gigantica was recorded from the study sites with the highveld having a significantly higher abundance of the snail species than the lowveld (P < 0.01). The snail population was low between December and March and started to increase in April reaching a peak in September/October. The number of juvenile snails peaked between April and August. The mean number of snails collected was negatively correlated with rainfall and positively correlated with temperature. Mean number of snails collected was also positively correlated with Potamogeton plant species and negatively correlated with Cyperus plant species. However, none of the L. natalensis collected from the habitats were found shedding Fasciola cercariae. Metacercariae were found on herbage from the fringes of the snail habitats between February and August for both years, with most of the metacercariae concentrated on herbage 0-1 m from the banks of the habitats. Based on the findings of this study, anthelmintic treatment should be administered in December/January to control chronic and mature fasciolosis. A second treatment should be given in April/May to reduce pasture contamination and subsequently snail infection, as this is the time the snail population starts to build up. To control acute fasciolosis due to the immature liver flukes a third treatment should be given in August. The first application of molluscicides to control the snail intermediate hosts can be done in June the time when the snail is harbouring the parasite and a second application in September in order to kill new generations of infected snails     

The influence of stocking rate and grazing system on the crude protein content and digestibility of Tarchonanthus veld in the northern cape 1

Abstract

Four stocking rates (10, 7, 6 and 4 ha/large stock unit), in both rotational and continuous grazing, have been applied with cattle on Tarchonanthus veld. The crude protein content and digestibility of organic matter of handcut samples and herbage samples collected by means of oesophageal fistulated steers in the different treatments, were determined.

The results indicated that the crude protein content (3,9 to 6,7%) and digestibility (48,7 to 59,4%) of handcut samples was not representative of the diet of grazing cattle. The crude protein content of the samples collected by means of oesophageal fistulated steers varied from an average of 13,6%. (October to December) to an average of 5,3% (July and August). On average, the digestibility of the fistula collected samples varied between 60,4% (February to April) and 50,2% (July to October). The crude protein content of the fistula collected samples tended to increase with increasing stocking rate while digestibility declined. Both crude protein content and digestibility of the fistula collected samples did not differ significantly between rotational and continuous grazing.     

Epidemiological studies of amphistome infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

During the period between January 1999 and December 2000, the distribution and seasonal patterns of amphistome infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Cattle faecal samples were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas, respectively. Patterns of distribution and seasonal fluctuations of intermediate host-snail populations and the climatic factors influencing the distribution were also determined by sampling at monthly intervals for a period of 24 months (November 1998 to October 2000) in six dams and six streams in the highveld and in nine dams in the lowveld communal grazing areas. Each site was sampled for relative snail density and the vegetation cover and type, physical and chemical properties of water, and mean monthly rainfall and temperature were recorded. Aquatic vegetation and grass samples 0-1 m from the edges of the snail habitats were collected monthly to determine the presence or absence of amphistome metacercariae. Snails collected at the same time were individually checked for the emergence of larval stages of amphistomes. A total of 16,264 (calves 5418, weaners 5461 and adults 5385) faecal samples were collected during the entire period of the study and 4790 (29.5%) of the samples were positive for amphistome eggs. For both regions the number of animals positive for amphistome eggs differed significantly between the 2 years, with the second year having a significantly higher prevalence (P < 0.01) than the first year. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), for adult cattle than calves (P < 0.01), and in the wet over the dry season (P < 0.01). Faecal egg output peaked from October to March in both years of the study. Bulinus tropicus, Bulinus forskalii and Biomphalaria pfeifferi were recorded from the study sites. The main intermediate host for amphistomes was B. tropicus with a prevalence of infection of 8.5%. However, amphistome cercariae were also recorded in Biom. pfeifferi and B. forskalii. Amphistome cercariae were recorded from both the highveld and lowveld areas with peak prevalence during the post-rainy season (March to May). Metacercariae were found on herbage from the fringes of the snail habitats between February and August, with most of the metacercariae concentrated on herbage 0-1 m from the edges of the habitats. Based on the epidemiological findings a control programme was devised. From this study, large burdens of immature flukes could be expected in cattle during the dry months. Since adult cattle would be resistant to the pathogenic effects of the migrating immature amphistomes the target for control would be young animals being exposed to the infection for the first time. Therefore, the first anthelmintic treatment can be administered in calves in mid June when maximum migration of immature amphistomes starting 3-4 weeks after infection in the early dry season would be expected. A second treatment could be given in late July or early August to remove potentially dangerous burdens of immature flukes acquired later in the dry season. Where resources permit, another strategy would be to treat against the mature flukes in March or April in order to reduce the number of eggs deposited on pastures and the opportunity for infection of the intermediate host snails. To reduce cercarial shedding by the intermediate host snails molluscicides can also be applied during the peak transmission periods (April/May and August/September).     

Parasites of domestic and wild animals in South Africa. XLI. Arthropod parasites of impalas,Aepyceros melampus,in the Kruger National Park

Ectoparasites were collected from impalas, Aepyceros melampus, at four localities within the Kruger National Park, namely Skukuza, in the Biyamiti region, Crocodile Bridge and Pafuri. Animals were also examined at Skukuza during a severe drought and at Skukuza and Pafuri towards the end of a second drought. Parasite burdens were analysed in relation to locality, sex, age class, month and drought. The impalas were infested with 13 ixodid ticks species, including two that were identified only to genus level. Except for four animals at Pafuri, all were infested with Amblyomma hebraeum. The highest intensity of infestation with larvae of this tick occurred from April to June and during November and December at Skukuza and in the Biyamiti region. Infestation with nymphs was highest during late winter. All animals were infested with Boophilus decoloratus, and the intensity of infestation was highest during spring. The intensity of infestation with Rhipicephalus appendiculatus was highest at Crocodile Bridge and at Pafuri, and that of Rhipicephalus zambeziensis at Skukuza. With both the latter species the intensity of infestation of larvae was highest from April to August, of nymphs from July to September or October and of adults during February and March. Rhipicephalus kochi was present only at Pafuri. The impalas also harboured five louse species and two species of hippoboscid flies. The intensity of infestation with lice tended to be greater during late winter and spring than during other seasons and greater on lambs than on yearlings on which it was greater than on adult animals.     

Nematophagous fungi in fresh feces of cattle in the Mata region of Minas Gerais state, Brazil.

The capacity to survive gut passage is one of the desirable characteristics for nematophagous fungi to be considered potential biological control agents of gastrointestinal nematodes of livestock. From April 1995 to April 1996, a pool of 10 cow fecal samples and 10 individual samples of feces from heifers, which were raised under partial (cows) or total (heifers) confinement in the Mata Region of Minas Gerais State, Brazil, were examined monthly for the presence of nematophagous fungi. A total of 10 isolates was found in the survey. Eight isolates were recovered from the pooled samples of cow feces and two from the individual samples of heifers. Fungi were present in the cow feces during the dry months of August (two isolates of Arthrobotrys oligospora and one Monacrosporium eudermatum) and September (one isolate of Harposporium lilliputanum and one of M. gephyropagum). Fungi were also recovered at the beginning and middle of the rainy season: one isolate of A. musiformis in October, and one isolate of M. gampsosporum and one unidentified fungus which produced septate hyphae and adhesive buds in December. In the individual samples collected from heifers, fungi were present only in the months of September (end of dry season) and March (end of rainy season). One isolate each of H. lilliputanum and A. oligospora were found, respectively. Additional studies to further characterize these isolates should be encouraged.     

A survey of seasonal patterns in strongyle faecal worm egg counts of working equids of the central midlands and lowlands, Ethiopia

A study was conducted for two consecutive years (1998–1999) to determine the seasonal patterns of strongyle infection in working donkeys of Ethiopia. For the purpose 2385 donkeys from midland and lowland areas were examined for the presence of parasitic ova. A hundred percent prevalence of strongyle infection with similar seasonal pattern of strongyle faecal worm egg output was obtained in all study areas. However, seasonal variations in the number of strongyle faecal worm egg output were observed in all areas. The highest mean faecal worm egg outputs were recorded during the main rainy season (June to October) in both years in all areas. Although an increase in the mean strongyle faecal egg output was obtained in the short rainy season (March–April) followed by a drop in the short dry season (May), there was no statistically significant difference between the short rainy season and long dry season (Nov–Feb) (P > 0.05). A statistically significant difference however, was obtained between the main rainy season and short rainy season, and between the main rainy season and dry season (P < 0.05). Based on the results obtained it is suggested that the most economical and effective control of strongyles can be achieved by strategic deworming programme during the hot dry pre-main rainy season (May), when the herbage coverage is scarce and helminthologically ‘sterile’, and the arrested development of the parasites is suppose to be terminating. This could insure the greatest proportion of the existing worm population to be exposed to anthelmintic and also reduces pasture contamination and further infection in the subsequent wet season.     

Seasonal development and survival of equine cyathostome larvae on pasture in south Louisiana

Cyathostome development and survival on pasture in subtropical climates of the US have yet to be completely defined and available data on seasonal transmission are minimal. In an attempt to study this phenomenon, a group of pony mares and their foals was maintained on a naturally contaminated pasture in southern Louisiana. Fecal egg counts (FEC) and numbers of infective third stage larvae (L3) kg(-1) dry herbage were recorded biweekly during two time periods, from January 1986 through December 1988, and September 1996 through October 1997. A FEC rise occurred during the late summer-early autumn which preceded the peak of L3 on pasture during the winter season. The numbers of cyathostome L3 were reduced during the hottest months of the year due mainly to daily minimum temperatures above 18 degrees C, and in winter during short freezing spells when daily minimum temperatures dropped below 0 degrees C. Tilling of the pasture reduced the number of cyathostome L3 during the early winter months but this is an efficacious measure only if horses are given an effective anthelmintic treatment prior to being returned to pasture. The data collected suggest that parasite reduction in southern Louisiana is possible using a treatment program with treatment beginning at the end of September and continuing through the end of March.     

Development and survival of infective larvae of gastrointestinal nematodes of cattle on pasture in central Kenya

On a series of pasture plots, 2 kg pats of bovine faeces containing known numbers of strongylid (Haemonchus, Cooperia, Oesophagostomum and Trichostrongylus) eggs were deposited at intervals of 4 weeks from July 1995 to June 1996. The plots were sampled every 2 weeks after contamination and infective larvae were identified and counted. Larvae of all the genera developed throughout the year, but the pats exposed during the rainy season yielded more abundant larvae on the herbage. Irrespective of the season of deposition of the pats, larvae were found in larger numbers from 2 to 6 weeks after deposition and generally declined to below detectable levels within 12 to 16 weeks of contamination. The comparatively short survival times noted in this experiment may present opportunities for manipulation of the population dynamics of the gastrointestinal nematodes in the tropical environment of Kenya.