Demonstration of the sustained anthelmintic efficacy of a controlled-release capsule formulation of ivermectin in weaner lambs under field conditions in New Zealand

Ten field trials were conducted in the North and South Islands of New Zealand to evaluate the anthelmintic efficacy and production responses attributable to treatment of weaner lambs with an intra-ruminal controlled-release capsule formulation of ivermectin. A total of 800 Coopworth, Perendale and Romney lambs weighing on average 20.8-34.8 kg were used. Lambs were either untreated or treated shortly after weaning with an ivermectin controlled-release capsule which delivers ivermectin at 0.8 mg per day for 100 days (minimum dose rate 20 microg/kg/day). Bodyweights, faecal nematode egg counts and dag scores (assessment of faecal soiling in the breech area) were determined before treatment and at about 4,8, 12, 14 and 16 weeks after treatment. Sheep treated with the Ivermectin capsule gained significantly more weight (11.6 kg) over the 16 weeks of the trials compared to untreated sheep (7.3 kg) (p < 0.01). Before treatment, faecal strongylid and Nematodirus spp. egg counts were equivalent (p > 0.10) but, at each time point thereafter, egg counts in ivermectin capsule-treated sheep were significantly lower (p < 0.01 or p < 0.05). Dag scores were not different at the start of the trial (p > 0.10), but at the end of the trial control sheep had significantly greater dags (p < 0.05) than sheep treated with the ivermectin capsule. These findings indicate that treated animals contributed significantly fewer nematode eggs to the contamination of pasture and therefore pasture contamination should be significantly reduced for at least 112 days. The productivity of the ivermectin capsule-treated sheep over the I6 weeks of the trials was also significantly increased compared to salvage-treated controls. Furthermore, the presence of dags, which predispose sheep to blowfly strike in the breech area and result in production losses due to the costs of dagging and downgrading of breech wool, were also significantly (p < 0.05) reduced in the ivermectin capsule-treated sheep.     

Field trials evaluating ivermectin controlled-release capsules for weaner sheep and for breeding ewes

Objective To confirm the efficacy of ivermectin released from a controlled-release capsule administered to young sheep and to breeding ewes under field conditions. Design Randomised field trials. Procedure In each of ten field trials 25 weaned lambs were treated with ivermectin controlled-release capsules and 25 remained untreated. Eight similar field trials were conducted using adult ewes. Efficacy against infections of gastrointestinal nematodes was assessed by faecal egg counts and faecal larval culture. Body weights were recorded and faecal soiling of the breech wool (dags) was assessed. Results Nematode faecal egg counts in the two groups were not different (P = 0.13) before treatment in the weaner trials or before treatment in the ewe trials (P = 0.49), but thereafter eggs in the untreated sheep persisted, whereas counts in sheep given capsules were negligible (P ≤ 0.01). In the weaner trials, dag scores for the two groups were not different at the start of the trials (P = 0.18) but at the end, untreated sheep had significantly more dags (P = 0.04) than treated sheep. In the ewe trials, dag scores remained low in both groups. Weaners treated with the capsule gained 1.4 kg (95% CL: 0.7, 3.1) more weight over the 16 week trial period compared to untreated weaners (P = 0.01). Both groups of ewes lost weight as a result of parturition but the mean loss by week 16 was greater for untreated (3.7 kg) (95% CL: -5.1,-2.2) than for treated ewes (1.8 kg) (95% CL: -3.3, -0.4). The mean change in ewe body weight for the two groups was however not significant (P = 0.07). Differentiation of nematode larvae recovered from cultures of faeces from untreated animals indicated that the capsules were effective against the common parasites of sheep. Conclusion The capsule was efficacious against gastrointestinal nematodes judging from faecal egg counts. It has the potential to significantly reduce contamination of pasture with nematode eggs. Treated weaners had less dags for 16 weeks and gained more weight than untreated weaners.     

Diarrhoea in Merino ewes during winter: association with trichostrongylid larvae

SUMMARY A study on 3 farms, each having a preventive strategy for the control of nematode infections, determined the risk factors associated with diarrhoea among Merino ewes in winter. Comparisons were made among groups of mated and unmated ewes with and without treatment with controlled-release capsules containing albendazole. Diarrhoea was assessed from the accumulations of faeces around the breech (dag score) and related to worm egg counts, total worm counts and histopathological findings. The overall prevalence of severe dag in ewes not treated with a capsule was 26% (221/844). In comparison, only 2.7% of treated ewes had severe dag. The adjusted odds ratio on each farm indicated that untreated ewes were between 12 and 16 times more likely to be affected with severe dag than ewes treated with a capsule. The effect of lactation was significant on only one farm whereas initial body weight had no significant effect. There was no significant association between worm egg counts and the occurrence of severe dag. There were significantly more eosinophils in the small intestine of ewes affected with severe dag compared with unaffected ewes. There were no significant differences in mast cell and globule leucocyte numbers between affected and unaffected ewes. This study provides strong evidence that the main cause of diarrhoea among Merino ewes grazing winter and early spring pastures is the ingestion of trichostrongylid larvae even by sheep that have a well-developed protective immune response to these parasites. New strategies for the control of nematode infections are needed to prevent diarrhoea and dag formation in adult sheep.     

Production losses in Merino ewes and financial penalties caused by trichostrongylid infections during winter and spring

SUMMARY: The productivity of Merino ewes treated with ivermectin and a controlled-release capsule containing albendazole was compared with untreated ewes grazing the same pastures on each of 3 farms. Treated breeding ewes had significantly increased greasy fleece weights (GFW, 6.5% and 7.1%) compared with untreated breeding ewes, on 2 of 3 farms but treatment caused no significant increase in the GFW of non-breeding ewes. Other benefits of treatment on all farms were a significant increase in body weight gain (from 1.7 to 3.7 kg) and a significant decrease in the weight of dag removed at crutching (from 42 to 622 g). These benefits occurred despite the presence on each farm of worms resistant to benzimidazoles. One disadvantage of treatment was an increase in mean fibre diameter of wool from treated ewes of from 0.12 to 0.41 μm. This increase reduces the value of the wool. Partial budgets indicated a net loss of from 8 to 62 cents per ewe for treatment. However, potential benefits such as increased growth rate and wool production from lambs of treated ewes were not included in the analysis. On one farm ewes were classified as ‘susceptible’ to severe dag if they had a dag score ≥ 4 at the time of capsule treatment. Ewes classified as ‘susceptible’ were about 7 times more likely to develop severe dag than were other ewes. There was no significant difference between the GFW of untreated ‘susceptible’ ewes and untreated ewes not classified as ‘susceptible’. Additionally, the response of GFW to treatment was no different to the response seen in ewes that were not classified as ‘susceptible’. The direct cost of diarrhoea and dag formation in Merino ewes was estimated to be 18, 30, 53, 86, 98 and 145 cents per head for ewes with a dag score of 0, 1, 2, 3, 4 and 5, respectively. This cost did not include potential benefits from reduced risk of breech strike, or intangible benefits associated with the improved welfare of sheep.     

An ivermectin tablet for sheep: Efficacy against gastro-intestinal nematodes and a bioavailability comparison with a liquid ivermectin formulation

An ivermectin tablet for o ral administration to sheep was developed for use in countries where it is customary to treat sheep with anthelmintic tablets. Tablets require no special administration equipment, and offer convenience for storage and transport. The ivermectin tablet, which delivers 10 mg of ivermectin (200 μg kg⁻¹ in a 50 kg sheep), had similar bioavailability to a liquid formulation of ivermectin (IVOMEC^® Liquid for Sheep) as determined by peak plasma ivermectin concentrations and area under the concentration curve in plasma (P>0.10). In dose confirmation trials in which nematode infections were induced in helminth-naive sheep, animals treated with the ivermectin tablet had significantly fewer adult and fourth-stage larval nematodes than untreated control sheep P<0.01 with efficacies >99% against all nematode species tested. In six field trials evaluating the efficacy of the ivermectin tablet in 240 Merino sheep, the reductions in faecal nematode egg counts ranged between 98 and 100%, as determined by comparison of pre- and post-treatment counts for the ivermectin-treated group.     

Efficacy of ivermectin in a controlled-release capsule for the control of breech strike in sheep

Objective To investigate the efficacy of ivermectin in an intraruminal controlled-release capsule (CRC) against blowfly strike.
Design Pen and field trials with controls.
Animals Pen studies: Two breech strike trials involving 60 Romney and 60 Merino sheep. One body strike trial using 100 Merino sheep.
Field trials: Eight trials in New Zealand used 1000 Romney and Romney-cross sheep. Fifty Merino lambs in one trial in Australia.
Procedure Pen studies: Sheep were allocated to two equal groups. One was not treated, the other sheep received a CRC that delivered ivermectin at 20 μg/kg/day for 100 days. In the breech strike trials, each animal was given an oral laxative 2 days before exposure to adult Lucilia cuprina . In the body-strike trial, the sheep sheep were kept wet to increase susceptibility prior to the release of blowflies.
Field trials: Fifty or 200 sheep allocated to equal groups of nontreated or treated with the CRC and grazed at pasture exposed to natural blowfly challenge.
Results Pen studies: Breech strikes developed in 24 of 60 controls but in none of 60 CRC-treated sheep. There was a 35% reduction in the number of CRC-treated sheep struck on the body.
Field trials: The average number of breech strikes in CRC-treated sheep was reduced by 86% (P < 0.001). The number of body strikes in the treated groups was a reduced by 27% (P < 0.05).
Conclusion The ivermectin CRC is a useful aid in controlling breech strike, but provides only moderate reduction in the incidence of body strike.     

Control of gastro-intestinal parasitism in sheep with ivermectin delivered via an intraruminal controlled-release capsule

The efficacy of ivermectin delivered by an intraruminal controlled-release capsule against gastro-intestinal nematodes of sheep was evaluated under controlled conditions. In seven Australian studies involving 170 Merino or Merino x Border Leicester sheep, intraruminal capsules developed for 20-40 kg or 40-80 kg sheep, and delivering 0.8 or 1.6 mg of ivermectin/day respectively for 100 days (minimum dose 20 microg/kg/day), were evaluated. Studies were designed to test the therapeutic efficacy against naturally acquired and induced infections treated at the adult and fourth larval stage, and the prophylactic efficacy against naturally acquired and induced infections with third stage infective larvae. The predominant pathogenic nematodes of sheep were represented. Two studies included known benzimidazole- and levamisole-resistant nematode strains. Sheep were necropsied for total nematode counts 21-8.5 days after treatment. The efficacy of the ivermectin controlled-release capsule was generally >99% against all nematode species tested, including those confirmed to be benzimidazole- and levamisole-resistant. High therapeutic activity was demonstrated against existing adult and fourth larval stage nematode infections at the time of treatment, and high prophylactic efficacy was shown against incoming third stage larvae of all species and strains tested.     

The effects of ivermectin and moxidectin on egg viability and larval development of ivermectin-resistant Haemonchus contortus

The in vivo effects of ivermectin and moxidectin on egg viability and larval development of ivermectin-resistant Haemonchus contortus were examined over time after anthelmintic treatment of sheep. Twenty merino sheep, (12 months old) were allocated to five treatment groups and infected with ivermectin-resistant H. contortus. Thirty one days later, the sheep were treated with intraruminal ivermectin capsules, oral ivermectin, oral moxidectin or injectable moxidectin at the manufacturer's recommended dosages, or left untreated. At various times up to 112 days after treatment, faecal egg counts (FEC) were determined and development rates of infective larvae (L3) cultured in faeces or on agar were measured. Eggs in faecal cultures from ivermectin capsule treated sheep showed reduced L3 development percentages in comparison to faecal cultures from untreated sheep. Eggs from ivermectin capsule treated sheep, isolated from faeces, and cultured on agar showed similar L3 development to eggs from control sheep. These results demonstrate an inhibitory effect of excreted ivermectin in faeces on larval development of ivermectin-resistant H. contortus. L3 development in faecal culture from animals receiving oral ivermectin were reduced for only 3 days after treatment. Faecal egg counts and development of L3 larvae in both culture systems from moxidectin treated sheep were low, due to the high efficacy of the drug. Egg counts in moxidectin treated sheep were reduced by approximately 90% 24h after treatment, before decreasing to almost 100% at 48h, suggesting that the current quarantine recommendation of holding sheep off pasture for 24h after treatment may still lead to some subsequent pasture contamination with worm eggs.     

Use of a long acting injectable formulation of moxidectin to control the periparturient rise in faecal Teladorsagia circumcincta egg output of ewes

A field study was conducted in a sheep flock in the south east of Scotland with a history of ivermectin resistance in Teladorsagia circumcincta. The objective of the study was to compare the effects of single anthelmintic treatments in ewes before turn-out onto pasture that was contaminated with a moderate level of overwintered, ivermectin resistant, T. circumcincta infective larvae. The ewes were treated according to label directions with either a long acting injectable formulation of moxidectin (1mg/kg; affording up to 14weeks persistent action against macrocyclic lactone (ML)-susceptible T. circumcincta) or an oral formulation of moxidectin (0.2mg/kg; affording up to 5weeks persistent action against ML-susceptible T. circumcincta). The lambs were enrolled in the normal management of the farm, and received a total of three oral ivermectin treatments during the 16week study. The efficacy of both treatment strategies in controlling the periparturient rise in faecal nematode worm egg counts and subsequent pasture contamination was assessed from the faecal worm egg counts of the ewes and their lambs between lambing and weaning. Ewes that were treated with the oral formulation of moxidectin shed approximately 3.5 times more T. circumcincta eggs between lambing and weaning than ewes that were treated with the long acting formulation of moxidectin. This difference was reflected in the faecal worm egg counts of the lambs that were grazed alongside the different treatment groups of ewes. The results of the current study demonstrate persistent efficacy of the long acting formulation of moxidectin against an ivermectin resistant T. circumcincta population. The decreased pasture contamination after treatment could lead to improved lamb growth and a need for fewer anthelmintic treatments, thus potentially reducing one possible selection pressure for anthelmintic resistance. However, treatment with the long acting formulation of moxidectin would give rise to fewer susceptible nematodes being present in refugia, which could increase another possible selection pressure for anthelmintic resistance, depending on the subsequent grazing management of that pasture. The rationale for use of a persistent anthelmintic drug to control the periparturient rise in faecal ML-resistant T. circumcincta egg output of the ewes is discussed and potential differences in selection for macrocyclic lactone anthelmintic resistance using the different formulations of moxidectin are acknowledged.     

Effects of a controlled-release albendazole capsule on parasitism and production from grazing Merino ewes and lambs

SUMMARY: Effects of a controlled-release albendazole capsule (CRC) on nematode parasitism and production of Merino ewes and lambs were Investigated in a replicated grazing experiment between August 1986 and July 1989. The experiment was conducted on a site where the naturally occurring parasites were benzimidazole-resistant, with double the recommended dose of oxfendazole reducing faecal egg counts of Trichostrongylus colubriformis by less than 50%. Two CRC treatments were compared with a minimal treatment control and the widely-used strategic control program, Wormkill.
Egg counts and worm burdens of major parasite species of ewes and of lambs before and after weaning were significantly reduced by use of the CRC in ewes before lambing or in lambs at weaning. These parasitological effects were reflected in increased productivity of CRC ewes and lambs. Ewes given CRCs lost less weight and grew more wool during lactation than ewes given Wormkill or control treatments, while their lambs gained more weight and had heavier fleeces than lambs from Wormkill or control treatments. Where lambs were weaned by removing ewes from the lambing paddock, administration of the CRC at weaning to lambs whose dams had also been treated with the CRC did not result in improved production when compared with lambs from ewes dosed with CRCs and treated after weaning according to the Wormkill program. Some possible uses for the CRC in ewes and lambs were identified.     

Comparison of the anthelmintic efficacy of oxfendazole or ivermectin administered orally and ivermectin administered subcutaneously to sheep during the periparturient period

The suppression of nematode egg output in faeces was measured in ewes treated just before lambing with either oxfendazole or ivermectin by oral drench or with ivermectin by subcutaneous injection. Ivermectin and oxfendazole given orally were similarly effective, whereas ivermectin given by subcutaneous injection extended the period of suppressed egg output by about one week. The more persistent anthelmintic effect of ivermectin given subcutaneously was probably due to its extended half-life in the plasma of treated sheep. Plasma pepsinogen activity was less in the sheep given anthelmintic than in the untreated controls. Ivermectin caused a significantly greater reduction in pepsinogen activity than oxfendazole and was more effective when given subcutaneously than when given orally.     

Comparison of ivermectin, oxfendazole and levamisole for use as anthelmintics during the periparturient period in sheep

Ewes synchronised with progestin impregnated sponges to reduce the spread of lambing were treated during the periparturient period with anthelmintic. The suppression of nematode egg output in faeces was measured in ewes given ivermectin either by subcutaneous injection or orally, or oxfendazole or levamisole orally. Ivermectin and oxfendazole reduced the output of eggs in the faeces of the ewes significantly (P less than 0.05) and the period of suppressed egg output was extended when ivermectin was given by subcutaneous injection. Plasma pepsinogen activity was estimated as a measure of abomasal damage. Pepsinogen values were significantly (P less than 0.001) lower in those animals treated with ivermectin by subcutaneous injection than in control animals. Levamisole showed a poorer response in terms of the output of eggs in faeces than either ivermectin or oxfendazole.     

Production benefits from pre- and post-lambing anthelmintic treatment of ewes on commercial farms in the southern North Island of New Zealand

Abstract

AIMS: To measure the magnitude and variability in production responses to anthelmintic treatments administered to adult ewes around lambing.

METHODS: Ewes carrying twin lambs, from sheep and beef farms (eight in Year 1 and six in Year 2) in the Wairarapa region of New Zealand, were enrolled in 14 trials (part of an experiment carried out on one farm in one year). Experiment 1 compared ewes treated 2–4?weeks pre-lambing with a controlled release capsule (CRC) containing abamectin, albendazole, Se and Co, to ewes injected pre-lambing with a long-acting Se plus vitamin B₁₂ product, and to untreated ewes. Experiment 2 included these treatments, plus a CRC administered at pregnancy scanning. Experiment 3 included the same treatments as Experiment 1, plus administration of a CRC containing albendazole, Se and Co, injectable moxidectin or oral derquantel plus abamectin, all administered pre-lambing, or oral derquantel plus abamectin administered 4–6?weeks after lambing. Variables compared were ewe liveweight at weaning and pre-mating, lamb liveweight at weaning, total weight of lamb weaned per ewe and ewe dag score at weaning.

RESULTS: Ewes treated with a CRC pre-lambing were heavier than untreated ewes (mean 3.2?kg) at weaning in 12/14 trials, and pre-mating (mean 2.8?kg) in 9/14 trials (p<0.001). Compared with mineral-treated ewes the mean difference was 2.8?kg pre-lambing (9/14 trials) and 1.7?kg pre-weaning (6/14 trials). Lambs reared by treated ewes were heavier (mean 1.55?kg) at weaning in 6/14 trials (p<0.001), but there was no effect of CRC treatment on total weight of lambs weaned per ewe (p=0.507). Variation in weight of lamb weaned per ewe was largely explained by differences in lamb survival from birth to weaning (p<0.001), with no effect of CRC treatment (p>0.65).

Treatment of ewes with a CRC at pregnancy scanning was neither better nor worse than a pre-lambing treatment (p=0.065).

There was no difference in the response from treatment with either of the two CRC or moxidectin. Treatment with short-acting oral anthelmintics resulted in no consistent benefit.

CONCLUSIONS: Anthelmintic treatments administered to ewes around lambing resulted in variable responses between farms and years, which in some trials were negative for some variables, and some of the variability was due to the mineral component of the CRC. The widespread perception amongst farmers and veterinarians that anthelmintic treatment of ewes around lambing will always result in positive benefits is not supported.     

Efficacy of repeated doses of levamisole, morantel, fenbendazole, and ivermectin against gastrointestinal nematodes in ewes

Levamisole, morantel, fenbendazole, or ivermectin was administered at 2-week intervals from May 1 through Sept 14, 1985, to breeding ewes (20 ewes/drug) infected with various gastrointestinal nematodes. All ewes had fewer gastrointestinal nematode eggs per gram of feces (epg) after 2 treatments, compared with pretreatment epg counts. Ewes administered ivermectin continued to have a low mean epg (0 to 3) throughout the study. The mean epg counts of ewes treated with levamisole increased from 3 to 483 during the study. This increase was similar to that of ewes treated with morantel (7 to 485 epg). The mean epg count of fenbendazole-treated ewes increased from 4 to 192 during the study. By the end of the study, the mean epg counts when expressed as a percentage of the pretreatment epg counts were 4% (ivermectin), 249% (fenbendazole), 627% (levamisole), and 630% (morantel). With the exception of the ivermectin-treated ewes, the epg count increased almost linearly in the ewes after the 2nd anthelmintic treatment. These data indicate that the gastrointestinal nematodes (including Haemonchus contortus) may have developed more resistance to levamisole and morantel than to fenbendazole. On the basis of the epg counts, resistance to ivermectin did not develop during the 4.5-month treatment period. The percentage of ewes shedding eggs after 2, 4, and 6 anthelmintic treatments was lowest for ewes treated with ivermectin (20%) and was similar (40%) for ewes treated with 1 of the other 3 anthelmintics. At the conclusion of the study, most of the ewes (90%) were shedding at least a small number of eggs, regardless of the anthelmintic treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficacy of ivermectin controlled-release capsules for the control and prevention of nasal bot infestations in sheep

Objective To investigate the therapeutic and prophylactic efficacy of an ivermectin controlled-release capsule against nasal bots (Oestrus ovis) in sheep.
Design Trial 1 – A pen study with controls. Trial 2 – A field study with controls.
Animals Trial 1 – Forty Merino wethers with natural infestations of nasal bot were used. Trial 2 – One hundred nasal bot-free wethers were used.
Procedure Trial 1 – Ten randomly selected animals were slaughtered and the heads split and examined to confirm bot infestation. Fifteen animals were allocated to untreated controls and 15 to treatment with a controlled-release capsule delivering ivermectin at ≥ 20 μg/kg/day for 100 days. Twenty-nine days after treatment the sheep were killed and examined for nasal bots. Trial 2 – Nasal bot-free sheep were allocated to two groups of 45 animals. One group was untreated the other sheep were treated with capsules as above. The sheep were grazed as a single group exposed to natural challenge from O ovis . Ninety days after treatment the animals were slaughtered and examined for nasal bot infestation.
Results Trial 1 – Live O ovis larvae were recovered from 60% of control sheep. No live larvae were collected from treated sheep. Trial 2 – Forty-one percent of untreated sheep harbored nasal bot infestations. No live larvae were collected from any treated animal.
Conclusion Treatment with a single ivermectin controlled-release capsule was 100% effective against existing infestations of O ovis and as a prophylactic treatment for this parasite.     

Comparison of worm control strategies in grazing sheep in Denmark.

Control of nematode parasites with reduced reliance on the use of anthelmintics was studied in 16 ewes with suckling twin lambs on contaminated pasture in Denmark. Ewes and lambs were treated with albendazole at turn-out 3 May. Ewes were removed from the groups on 26 July, and lambs were slaughtered on 11 October. The animals were allocated to 4 groups of 8 lambs and their 4 ewes. Group TS was treated with albendazole at weeks 3, 6 and 8 after turnout and set-stocked; group TM was similarly treated but moved to clean pasture in conjunction with the last drenching; group US was untreated and set-stocked, and group UM was left untreated but moved to clean pasture week 8 after turn-out. Supplementary feed was offered in June and August due to scarcity of pasture. Strategic treatments of ewes and lambs weeks 3, 6 and 8 after turn-out, with or without a move to clean pasture, were highly effective in controlling nematode infections for most of the season. This was reflected in better weight gains and carcass characteristics in the treated compared to untreated lambs, resulting in an average increase in the value of the product by 36%. The effect of moving without treatment (UM) on faecal egg counts was limited but peak pasture infectivity was reduced to less than 10% compared to the set-stocked group and weight gains of lambs were significantly better despite poor feed availability in late season. The study showed that under set-stocked conditions repeated anthelmintic treatments of both ewes and lambs in early season may ensure sufficient nematode control whereas moving animals to clean pasture without dosing was less efficient. The latter may, however, still be a viable option in organic and other production systems where routine use of anthelmintics is banned, particularly if weaning and moving are combined or a second move is performed.     

Worm infections in high and low bodyweight Merino ewes during winter and spring

Objective   To compare infections of gastrointestinal nematodes in 2-year-old ('maiden') spring-lambing Merino ewes in the upper and lower 25% of body weights (BW) at joining.
Design   An observational study over two consecutive years on two farms in western Victoria.
Methods   On each farm, ewes were weighed at the end of mating. Ewes within the upper and lower quartile of BW formed two groups that grazed together for the remainder of the year. On each farm, 20 ewes from each group were also treated with controlled release capsules containing ivermectin to minimise the effects of parasitism. Measures of worm infections were worm egg counts, total worm counts and assessment of breech soiling ('dag score'). Measures of production were BW, numbers of deaths, pregnant ewes and weaned lambs in each group, and response to treatment with a capsule.
Results   No consistent difference was found in mean worm egg counts between ewes in the high and low BW groups and total worm counts of ewes before lambing were not significantly different in either year. Breech soiling of low BW ewes was consistently higher on both farms in both years. Those ewes also reared 7% to 14% fewer lambs. The difference in BW between the low and high groups remained highly significant on both farms throughout both years.
Conclusion   A strategic approach to worm control is appropriate for ewes in both high and low BW categories. Management options for low BW ewes include culling, supplementary feeding to increase BW before mating, or delaying mating for 12 months.     

Production and immunological responses associated with controlled-release-capsule vs 5-drench preventive anthelmintic programmes for parasite control in lambs

AIMS: To determine whether: a) using a controlled-release anthelmintic capsule (CRC) instead of a programme of 5 oral drenches administered at 3-4 week intervals, would delay the development of anti-parasite immunity in lambs; b) the use of ivermectin instead of albendazole, administered either as a CRC or as a programme of 5 oral drenches, would delay the development of anti-parasite immunity in lambs; c) lambs treated with CRCs would have higher liveweight gains than lambs drenched orally 5 times at 3-4 week intervals, and; d) delayed onset of anti-parasite immunity is associated with reduced liveweight gains in the period following anthelmintic treatment. METHODS: Three field trials were conducted, 1 on a research farm and 2 on commercial sheep farms, in which groups of 30 lambs were treated with either a CRC containing albendazole, a CRC containing ivermectin, 5 oral drenches with albendazole, or 5 oral drenches with ivermectin, administered at 3-4 week intervals. Liveweights and faecal nematode egg counts (FECs) were recorded in all trials. Immunoglobulin-G (IgG) antibody levels to Ostertagia circumcincta and Trichostrongylus colubriformis adult and larval antigens were measured in Trials 1 and 3, and fleece weights and resistance of animals to nematode challenge infection were measured in Trial 1. RESULTS: CRC-treated lambs had higher levels of antibodies to O. circumcincta infective-stage larvae (L3) than orally drenched lambs in Trial 3, but no other immunological differences due to mechanism of delivery were detected. Antibody levels were lower in lambs treated with ivermectin than albendazole, as a CRC or oral drench in Trial 1, but this was not associated with any measurable effects on FEC or productivity. No significant differences (p>0.05) were detected between drench types (albendazole vs ivermectin) or delivery mechanisms (CRC vs oral drenching) in any of the production parameters measured, in any of the trials. Albendazole-CRCs failed to control FECs in all 3 trials. CONCLUSIONS: Although some differences between treatments in antibody levels were detected these were not associated with measurable differences in level of parasitism or productivity of lambs. CRC use did not appear to offer substantial gains in productivity over a structured programme of 5 oral drenches administered at 3-4 week intervals.     

The efficacy of a controlled-release albendazole capsule in suppressing nematode burdens in sheep

An experiment was undertaken between July and November 1985 in East Gippsland, Victoria, to determine the efficacy of an intra-ruminal controlled-release albendazole capsule against naturally acquired worm burdens and larval challenge in Merino hoggets. Two groups of 20 sheep, one group untreated, the other dosed with a capsule were grazed together; 5 sheep from each group were slaughtered for total worm counts 30 and 101 d after capsules were administered. Serum anthelmintic concentrations, faecal egg counts and body weights were monitored. Most capsules were exhausted within 91 d of administration. During the estimated 80 d for which they remained active the capsules were highly effective against the benzimidazole-susceptible worm populations. Faecal egg counts were reduced to zero and total worm populations were reduced by over 97% 30 d after administration. By 101 d egg counts were increasing and worm counts indicated that sheep were becoming reinfected. Sheep treated with the capsules grew faster than those not treated.     

The Effects of a Controlled-Release Albendazole Capsule (Proftril-Captec) on Parasitism in Grazing Corriedale Ewes in the Nyandarua District of Kenya

Munyua, W.K., Githigia, S.M., Mwangi, D.M., Kimoro, C.O. and Ayuya, J.M., 1997. The effects of a controlled-release albendazole capsule (Profitril-Captec) on parasitism in grazing Corriedale ewes in the Nyandarua district of Kenya. Veterinary Research Communications, 21 (2), 85-99The effects of intraruminal sustained-release capsules (IRSRCs) on parasitism in grazing Corriedale ewes were investigated over a period of 119 days (4 June-30 September 1993) using 40 ewes aged approximately 2 years and randomly divided into two groups of 20 ewes each. Each of the ewes in the treatment group received an IRSRC while the controls were left untreated. The groups were placed on adjacent 2.5-acre paddocks obtained by subdividing a 5.0-acre permanent pasture which had previously been grazed by young untreated sheep, so exposing both groups of ewes to a similar challenge from a contaminated paddock. The faecal egg counts, herbage larval counts and worm burdens of the major gastrointestinal parasites of sheep were significantly reduced by the use of the IRSRC. These parasitological effects were reflected in the increased live weight gains and heavier fleeces of the IRSRC-treated ewes. The control ewes required occasional salvage treatments during the trial period and the herbage on their paddock was heavily contaminated with infected larvae, reflected in the high worm burdens in the control ewes necropsied at the end of the trial and in tracer sheep introduced into the paddocks during the initial (day 30), interim (day 58) and final (day 89) stages of the experiment. Most capsules were exhausted within 95 days of administration, leading to a rise in the count of eggs per gram in the faeces in the treated group towards the end of the study.