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• W143342219 abstract "Gastrointestinal (GI) nematode parasitism causes major economic losses and animalhealth problems in farmed livestock and thus poses a serious challenge to livestockproduction worldwide. Parasite control strategies historically have relied heavily onanthelmintic drenches, but with the emergence of anthelmintic resistance, newstrategies are required. A number of forage species containing high concentrations ofcondensed tannins have been shown to have anthelmintic properties. The aim of thecurrent study was to determine whether selected tropical legumes used as proteinsupplements for livestock, and in particular Calliandra calothyrsus, might also beuseful for the control of GI nematode parasites.A pilot study was undertaken initially to determine the effects of Calliandra, whenfed to lambs as a sole diet, on burdens of Haemonchus contortus or Trichostrongyluscolubriformis and on egg production by adult worms. Lucerne (Medicago sativa)pellets were used as a high protein control diet and Mitchell grass (Astrebla species)hay was used as a low protein control diet. The effects of diet on the worms wereassessed by faecal egg counts and post-mortem worm counts. Worm burdens of eachspecies and egg production by H. contortus were similar in lambs on all three diets.However, egg production of T. colubriformis was reduced by 85-90 % by feedingCalliandra to the host lambs and the number of eggs in utero of femaleT. colubriformis was significantly increased.These results were confirmed and extended in a larger-scale feeding experiment, inwhich the Mitchell grass diet was omitted. A number of haematological parameterswere measured to examine the nutritional status, resistance and resilience of the hostlambs in response to the worm burdens. Because pH was expected to affect theability of condensed tannins to bind to worms, the pH was recorded immediatelyafter slaughter in each segment of the GI tract to examine the relationship betweenpH and faecal egg counts. Worm burdens of H. contortus were similar in lambs fedCalliandra (2237 ± 395 worms) and lucerne (1861 ± 230 worms). Worm burdens ofT. colubriformis were also similar in lambs fed Calliandra (5718 ± 339 worms) andviilucerne (4861 ± 452 worms). However, egg production by both H. contortus andT. colubriformis were reduced by 64-84 % and 24-68 % respectively. There were noimprovements in any of the haematological parameters measured attributable to thedifferent diets, indicating that reduced egg counts were due to a direct toxic effect ofthe Calliandra diet and not due to improved resistance or resilience to the worms.The variation in pH in each of the GI segments was too small to identify anyrelationship between pH and reduced egg output by female worms.A study was then conducted to confirm that the anthelmintic effects of Calliandrawere due to the condensed tannins in the plant. Condensed tannins were extractedand purified from Calliandra leaves and incubated with H. contortus and T.colubriformis eggs and larvae in in vitro assays. Egg hatch and larval developmentrates were determined. Calliandra tannins delayed hatching and reduced egg hatchand larval development in both species. Development of infective larvae was almostcompletely inhibited at tannin concentrations above 300 μg/mL.In vitro assays were also used to screen a number of other tropical legumes foranthelmintic activity. Crude extracts of nine legume species, including Calliandraand lucerne pellets, and two different fractions of purified Calliandra were incubatedwith H. contortus and T. colubriformis eggs and larvae. In addition to Calliandra,Leucaena leucocephala and Desmanthus virgatus were identified as having possibleanthelmintic activity against nematode eggs and larvae. The two Calliandra fractionsboth had similar anthelmintic activity to the Calliandra crude extract.In an attempt to determine the mode of action of Calliandra condensed tanninsagainst GI nematodes, a staining technique was developed to identify tanninshistologically in mammalian and nematode tissues. Haematoxylin & Eosin (H&E),ferric chloride, butanol-H2SO4 and vanillin-HCl techniques were examined, initiallyusing plant tissues, and then optimised for use in mammalian tissues. The H &E andvanillin-HCl techniques were then used to stain GI tissues and nematodes obtainedfrom Calliandra-fed lambs. In the ovine GI tissue, condensed tannins were present inthe lumen and in macrophages and giant cells in the lamina propria, particularly inthe abomasum. Condensed tannins were observed on the outside of the cuticle ofintact adult H. contortus and T. colubriformis, mainly in adherent digesta. Condensedtannins were also observed in the pharynx and intestine of sectioned H. contortus,but no condensed tannins were observed in the reproductive tract.A final experiment was conducted to determine the effects of Calliandra on thedevelopment, establishment and reproductive capacity of nematodes derived fromeggs exposed to the legume in the host diet but with no subsequent exposure asadults. Eggs of H. contortus and T. colubriformis obtained from Calliandra-fed orlucerne-fed donor lambs were cultured in vitro to obtain infective larvae, which wereused to infect groups of recipient lambs. Worm egg and larval production from thedonor lambs, and adult worm egg output and worm burdens of the recipient lambs,were monitored. Although worm egg production and larval production from thedonor lambs was reduced by the Calliandra diet, the ratio of eggs to larvae was alsoreduced. It was not clear whether this was due to problems with the experimentaltechnique or to selection pressure exerted on the worms by the Calliandra diet.Worm burdens were higher in the recipient lambs receiving larvae from theCalliandra-fed donors. Egg production by the female worms derived fromCalliandra-fed donors may have been reduced, but the results were not clear.Calliandra, in addition to its value as a source of protein for tropical livestock, maybe useful in reducing egg production by GI parasitic nematodes, thus reducing larvalcontamination of tropical pastures and infection rates of livestock. Calliandratherefore has potential as an anthelmintic alternative in tropical regions." @default.
• W143342219 created "2016-06-24" @default.
• W143342219 creator A5067321794 @default.
• W143342219 date "2007-01-01" @default.
• W143342219 modified "2023-09-27" @default.
• W143342219 title "Anthelmintic effects of tropical shrub legumes in ruminant animals" @default.
• W143342219 hasPublicationYear "2007" @default.
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