Ruminoreticulum bypass in goats and its possible effect
on the ef®cacy of oxfendazole against resistant
gastrointestinal parasites
N.D. Sargison
*, W.E. Pomroy, B.A. Adlington
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand
Accepted 10 July 1999
Abstract
Ruminoreticulum bypass was observed in 9±12-month old Angora goats using video-taped ¯uoroscopy. For experimental purposes, ruminoreticulum bypass was stimulated by yarding animals for 19±24 h before drenching, or by yarding and oral premedication with 2% cobalt sulphate solution. When bypass occurred, 50±100% of the drench was deposited in the abomasum. Ruminoreticulum bypass had no apparent effect on the faecal egg count reduction of benzimidazole resistant
Ostertagiaspp. following drenching with a standard dose of 5 mg/kg of oxfendazole, although the low frequency of bypass prevented any ®rm conclusions from being made. The importance of ruminoreticulum bypass to the ef®cacy of benzimidazole anthelmintics in goats may have been overemphasised. Published by Elsevier Science B.V.
Keywords:Goat; Anthelmintric; Ruminoreticulum bypass; Nematode; Oxfendazole
1. Introduction
There are major differences in the ef®cacy of anthelmintic drugs between goats and sheep (McKenna, 1984). Benzimidazole anthelmintics attain lower plasma concentrations and are eliminated more rapidly in the former species (Weir and Bogan, 1985; Bogan et al., 1987; Sangster et al., 1991). Doubling of the recommended sheep dose of oxfendazole has been successful against certain gastrointestinal parasites of goats, although the repetition of two or three doses at intervals of 12±24 h appears to be more effective (Bogan et al., 1987; Sanyal, 1998). Unfortunately,
such a strategy is unlikely to be perceived as a practical control option, therefore, alternative means should be considered to prolong the duration of effec-tive plasma concentrations of benzimidazole anthel-mintics in goats. Yarding for a period of 24 h before drenching may extend the plasma kinetics of oxfen-dazole in goats for the same reasons that have been described for sheep (Ali and Hennessy, 1995), although there are few data in support of this argument for goats. However, it has been suggested that yarding for 24 h could increase the incidence of ruminoreti-culum bypass (BrugeÁre et al., 1987; Mikhail et al., 1988), which may reduce the ef®cacy of some benzi-midazole anthelmintic drenches (Sangster et al., 1991). The aim of this pilot study was to determine Small Ruminant Research 35 (2000) 209±212
*Corresponding author.
the effect of ruminoreticulum bypass on the ef®cacy of oxfendazole against resistant parasites.
2. Materials and methods
Angora goats between the ages of 9 and 12 months, from a ¯ock with a history of multigeneric resistance to oxfendazole, were studied on two occasions in winter (July) and spring (September).
Individually tagged animals (n18, July;n19, September) were weighed and yarded for 24 h (July) or 19 h (September) before drenching to the back of the mouth with 5 mg/kg oxfendazole (Systamex; Mal-linckrodt) mixed with 49% w/v barium sulphate sus-pension to a volume of 3 ml/10 kg. Feed was withheld during yarding, but the animals had free access to water. The distribution of the oxfendazole between the ruminoreticulum and abomasum was determined by video-taped ¯uoroscopy (Sargison et al., 1998).
In the September study, 10 ml of 2% cobalt sulphate solution was administered to the pharynx of 10 ani-mals, 10 s before dosing, in an attempt to stimulate ruminoreticulum bypass (Sargison et al., 1999).
Faecal samples were collected from each animal pre-treatment (before yarding and drenching) and post-treatment (8 days after drenching). All faecal samples were collected within 2 h of removal of the goats from pasture.
Faecal egg counts were performed on each sample using a modi®ed McMaster technique where each egg counted represented 50 epg. The faecal egg count reductions were calculated for animals (n6, July; n3, September) in which >50% (20%) of the drench entered the abomasum, and for animals (n12, July; n16, September) in which all of the drench entered the ruminoreticulum. Bulk pre-and post-treatment faecal cultures were incubated at 27oC for 7 days to provide infective larvae for identi-®cation of resistant parasite genera.
3. Results
3.1. The incidence of ruminoreticulum bypass
Ruminoreticulum bypass of 50±80% (mean 60%) of the drench was observed in six of the 18 animals
which had been yarded for 24 h and in one of the nine animals (100% bypass) which had been yarded for 19 h and not premedicated with cobalt sulphate solu-tion. Ruminoreticulum bypass (80% and 100%) was observed in two of the 10 animals that had been yarded for 19 h and given 10 ml of 2% cobalt sulphate solu-tion to the pharynx 10 s before drenching. Ruminor-eticulum bypass was observed in different animals in the two studies.
3.2. The effect of ruminoreticulum bypass on anthelmintic ef®cacy
The incidence of ruminoreticulum bypass was too low on each occasion for an accurate comparison of anthelmintic ef®cacy to be made. However, ruminor-eticulum bypass of the oxfendazole to the abomasum had no apparent effect on the faecal egg count reduc-tion. The individual faecal egg counts are presented in Table 1. In the goats which were yarded for 24 h, the mean reduction in faecal egg count 8 days after drenching to the abomasum (n6) and ruminoreti-culum (n12) were 82% and 84% respectively. In the goats which were yarded for 19 h, the mean reduction in faecal egg count 8 days after drenching to the abomasum (n3) and ruminoreticulum (n16) were 60% and 63% respectively. The faecal egg count reductions should not be compared between the two occasions, because they were studied at different times.
Ostertagiaspp. were identi®ed as the only resistant parasite genus on both occasions. The bulk pre- and post-treatment larval culture results are presented in Table 2. The dose rate of 5 mg/kg of oxfendazole was, therefore, effective against susceptible Trichostrongy-lus spp.
4. Discussion
goats, based on studies in sheep (Clunies Ross, 1934; Sargison et al., 1998). In Australian ®eld trials a glucose marker technique was used to determine the incidence of ruminoreticulum bypass when Angora goats were drenched with an oral oxfendazole-equiva-lent volume, shortly after bringing in from pasture. Ruminoreticulum bypass was observed in 79% of goats of all ages between 1 month and 3 years (Sangster et al., 1991). The greater incidence of ruminoreticulum bypass in the Australian trials than in the current New Zealand study, may be attributed to
different management conditions or to differences in the accuracy of glucose markers and ¯uoroscopy to determine ruminoreticulum bypass.
The incidence of ruminoreticulum bypass in the ®rst nine animals to be studied in September was too low for experimental comparison of faecal egg count reductions. An attempt was made, therefore, to sti-mulate closure of the reticular groove using 10 ml of 2% cobalt sulphate solution administered to the phar-ynx 10 s before drenching. Cobalt sulphate was a useful stimulant of reticular groove closure in 10-Table 1
Individual faecal egg counts and mean faecal egg count reductions following drenching to the ruminoreticulum or abomasum
July (24 h off pasture) September (19 h off pasture)
Ruminoreticulum Abomasum Ruminoreticulum Abomasum
Pre-treatment
Post-treatment
Pre-treatment
Post-treatment
Pre-treatment
Post-treatment
Pre-treatment
Post-treatment
650 150 5200 250 900 300 1150 250
1200 100 150 0 200 100 1250 150
508 50 400 150 2700 600 200 650
3550 450 250 200 1150 600
250 0 950 0 650 150
1900 100 1400 900 1000 125
100 150 950 100
1300 925 1750 300
887 100 650 0
1750 250 0 100
1850 200 400 200
1150 0 550 50
1300 550
526 150
450 1200
350 500
Mean 1258 206 1392 250 845 314 867 350
Mean FECR 84% 82% 63% 60%
Table 2
Larval culture results
July September
Pre-treatment Post-treatment Pre-treatment Post-treatment
56%Trichostrongylus 100%Ostertagia 68%Ostertagia 100%Ostertagia
44%Ostertagia 30%Trichostrongylus
2%Haemonchus
month old lambs (Sargison et al., 1999), but did not reliably stimulate ruminoreticulum bypass in the goats. 2% copper sulphate might have provided better stimulation of the reticular groove re¯ex, but was not used because of its potential confounding anthelmintic effect (Clunies Ross, 1934).
Because of the low frequency of ruminoreticulum bypass, it was not possible to make ®rm conclusions about the effect of ruminoreticulum bypass on anthel-mintic ef®cacy. However, it is apparent that ruminor-eticulum bypass had little effect on the ef®cacy of 5 mg/kg of oxfendazole against resistant Ostertagia spp. helminths. In earlier studies, Sangster et al. (1991) and Chartier et al. (1995) demonstrated enhanced plasma kinetics of oxfendazole when the drug was administered directly into the rumen of goats when compared to direct abomasal administration, and concluded that ruminoreticulum bypass would be an important factor in determining the ef®cacy of oxfendazole. It is possible that any effect of rumi-noreticulum bypass is dependent on the resistant parasite species present.
The lower reductions in faecal egg counts in September (63% and 60%) than in July (84% and 82%) may be due to selection for benzimidazole resistance associated with the earlier anthelmintic treatment.
It is possible that the importance of ruminoreticu-lum bypass to the ef®cacy of benzimidazole an-thelmintics in goats has been overemphasised, although further study would be required to determine its effect when other resistant parasite genera are present.
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