Owen, N.C.

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SOME NUTRITIONAL ASPECTS OF HAEMONCHOSIS IN EXPERIMENTALLYINFESTED LAMBSProewe is uitgevoer om die invloed van eksperimentele hemonchose op die droe materiaalinname, massatoename, droe materiaal-verteerbaarheid en stikstofretensie by skape te bestudeer. Ses en 9 maand oud lammers is met 'n suiwer starn van besmetlike larwes vanHaemochus contortus (3de stadium) onder gekontroleerde toestande besmet. Besmette skape het 'n betekenisvolle afname in stikstof-retensie en tiroe materiaalverteerbaarheid getoon (P < 0,01). Hierdie veranderings was hoofsaaklik tot die 2de week en die latere gedeeltesvan die 6-week proefperiode beperk. Verminderde liggaamsmassatoename by besmette lammers was minder opvallend; moontlik verbergdeur oortollige vloeistofretensie. Droe materiaalinname was nie merkbaar beihvloed nie. Hierdie nadelige gevolge van hemonchose staan direkin verband met die graad van besmetting.Trials were conducted to study the effect of experimental haemonchosis on dry matter intake, live mass gain, dry matter digest-ibility and o.itrogen retention in sheep. Six and 9 month old lambs were infested with a pure strain of infective larvae of Haemonchuscontortus (:rd stage) under controlled conditions. Infestation resulted in significant decreases in nitrogen retention and dry matter digest-ibility (P < 0,01). These changes were mainly confined to the 2nd ~eek and the latter stages of the 6 week experimental period. Decreasedbody mass gains by the infested lambs were less prominent; possibly being obscured by excessive fluid retention. Dry matter intake wasnot markedly influenced. These deleterious effects of haemonchosis are directly related to the severity of infestation.Internal parasites are responsible for considerableeconomic losses to the sheep industry in South Africa andelsewhere. Apart from the mortality resulting directly frominfestationevengreaterlosses probably stem from a loweredproductivity due to reduced feed utilization. This latteraspect has been demonstrated with intestinal parasites bothas pure (Horak & Clark, 1964) and as mixed infestations(Shumard, Bolin & Eveleth, 1957). In general, however,this feature of verminosis appears to have received littleattention. In the case of haemonchosis, the principalnutritional aberration has been described as anorexia inboth pure (Evans, Blunt & Southcott, 1963) and mixedinfestations where Haemonchus contortus was prominent(Clark, Ortlepp, Bosman, Laurence, Groenewald & Quin,1951; Shumard et al. 1957). Further observations onnutritional aspects of a pure infestation of H. contortusin lambs f'Jrm the basis of this report.Two separate trials were conducted using SouthAfrican Mutton Merino lambs reared and housed underworm-free conditions.Four 9 months old lambs were each infested with50 000 third stage larvae of H. contortus (Owen, 1968),while 4 uninfested lambs acted as controls. All sheep were*Present address: Department of Physiology, Faculty ofVeterinary Science. Onderstepoort.housed individually and fed milled lucerne hay. The housingwas so arranged that the feeding of each infested animalcould be paired with that of a control. Each morning aninfested animal received more feed than it would consumethat day. The next morning the amount eaten (air dry)was offered to the respective control animal. Feed samples,feed refusals and faeces were collected for each alternateweek following infestation. Weekly live masses were record-ed for the duration of the 6 week trial period, and all sheepwere finally autopsied for total worm counts as describedby Reinecke, Horak & Snijders (1963).In this instance 6 four months old lambs were used.Three were infested with larvae of H. contortus as beforeand three were left uninfested as controls. All the sheepwere housed in metabolism cages and fed milled lucernehay (16% crude protein) ad libitum. Dry matter intake andlive mass gains were recorded on a weekly basis. The dailyfeed ration was weighed out for each sheep prior to com-mencement of the experiment. At this time random feedsamples were taken for subsequent analysis and computa-tion of nitrogen intake. Feed refusals, faeces and urinesamples were collected and pooled for each week. Thesewere subsequently analysed for nitrogen content. Drymatter digestibilities and nitrogen balances were calculatedfor each week of the experiment in the standard way. Thenitrogen content of the samples was determined by theKjeldhal method. At the end of the experiment, totalTwo lambs developed mild infestations, while theremaining 2 were more severely affected. The worm burdensestablished at the end of the trial period together with theeffect of mild and severe infestation on mean dry matterintake and live mass gain per week are presented in Table I.All sheep showed some variation in apparent drymatter digestibility during the course of the experiment.Hence, the experimental error was determined on the con-trol sheep after removing "between sheep" and "betweenweek" variation. The decrease in apparent dry matterdigestibility of hay by an infested sheep was then com-pared with the mean decrease for the controls during thesame period by t-test. Sheep I showed a significant decreaseduring the second and third week after infestation.The mean increase in dry matter consumption perweek did not differ significantly between infested andExperimental group Adult H. contortus Parameter*at autopsy(mean) (mean)OMControl Nil L.M.G. 1.5OM 9,28Mild 635 L.M.G. 1,5OM 11.98Severe 7208 L.M.G. 1,7as for respective pair mate **0,5 1,0 l.3 2,0 1,09,38 10,02 10,09 10,951.0 1,4 1,3 0,9 1,612,24 12,83 13,04 12,46 12,71-1,0 1,2 1,5 2,6 -0,3*OM denotes dry matter consumption (Kg/week).L.M.G. denotes live mass gain (Kg/week).**Feeding paired in this experiment.The results show that the severely infested sheep lostmass during the 2nd and 6th weeks of the experiment whilethe mildly infested sheep continued to gain mass through-out. The mean mass gain per week was significantly greater(P < 0,05) for the mildly infested animals. The mildly infest-ed and control sheep did not differ in this regard. In bothinfested and control groups the dry matter intake increasedprogressively each week and did not differ significantly.Facilities only permitted comparison of the mildlyinfested lambs and their respecitve controls with regardto apparent dry matter digestibilities. These were foundto remain virtually constant at 60 % and 58 % for the in-fested and control sheep respectively. This difference wasnot statistically significant.The severity of infestation again varied betweenindividual animals. Two of the infested lambs developedsevere haemonchosis, while the third was only mildlyaffected. The degree of infestation of the individualanimals and the calculated apparent dry matter digestibil-ities are given in Table 2.Degree of infestation and apparant dry matter digest-ibilities of lucerne hay by experimental sheepSheepNo. contortusrecoveredat autopsyInfested1 64 40*** 49** 59 57 56 94702 63 61 68 60 61 54 74103 60 48 57 61 62 58 2750Control4 64 55 61 60 55 58 Nil5 62 53 61 60 53 58 Nil6 58 53 54 59 57 56 Nilcontrol sheep. However, the infested sheep did show atransient loss of appetite during the second week afterinfestation. The results obtained from nitrogen balancecalculations are shown in Table 3.Both groups of sheep showed a mean positivenitrogen retention over the experimental period (Infested:Infested1 56,5 -23.6*** 37,8 8,6* 24,1 - 1,3**2 75,9 38,1 * 70,7 39,6 19,0** 23,8*3 37,0 18,5 41,8 18,7 23,3 41,1Control4 72,2 45,9 53,4 12,3 29.2 29.85 73,8 38,3 61,2 44,3 35,1 42,76 44,1 40,0 25,1 36,4 21,4 18,4333231~30III~ 29u&~ 28~272625032.3 ± 18 gN/week; control: 40,2 ± 13 gN/week).Analysis0[ the results (see apparent dry matter digestibility)showed a significant decrease in nitrogen retention forboth the severely infested sheep during the second week andagain towards the end of the experiment. The mostseverely infested lamb (1) actually went into negativenitrogen balance during the second and sixth weeks.The mean live mass gains of infested and controlgroups did not differ over the experimental period. How-ever, the infested sheep lost live mass during the secondweek while the uninfested animals continued to gain inmass. Hereafter, during the third and fourth weeks, theinfested sheep gained markedly in body mass. This trendis illustrated in Fig. I.The ircrease in live mass coincided with significantlyincreased plasma volumes in the 2 more severely infestedsheep from the 20th day onwards. Sheep 2 developed amarked submandibular oedema at this time and passedabnormally large amounts of urine. These aspects of thepathogenesi~ of haemonchosis have been fully dealt with inThe significant features of these trials are decreasednitrogen retention and live mass loss. This is especiallyprominent during the second week after infestation. Afurther decrease in nitrogen retention occurs at about thesixth week of parasitism. These periods correspond to thefourth larval moult and the adult stage of the parasite's lifecycle respectively (Veglia, 1915).The apparent absence of a decrease in live mass insome severely affected sheep (Trial 2) may be ascribed toexcessive fluid retention after about the third week whenclinical oedema may appear. The parasitized animal appearsto increase its extracellular fluid volume in compensationfor the reduction in red cell volume as the anaemia pro-gresses (Owen, 1968).The initial decrease in nitrogen retention may be dueto the onset of mucosal damage caused by the larvae(Charleston, 1965) resulting in impaired protein digestion.This period coincides with a systemic reaction as evidencedby the distinct eosinophilia (Owen, 1968). Little informa-tion is available on the effect of the parasite on abomasalfunction. Charleston (1965) failed to show any pH changesin the abomasum during the first 20 days of parasitism,while Chistrie, Brambell & Mapes (I 967) demonstrateda marked increase in pH 72 to 76 hours after infestation.H. contortus infestation did not appear to affect Vitam.inB12 absorption suggesting an unimpaired intrinsic factormechanism (Owen, Neethling & Terblance 1971). Proteinloss by exudation from the damaged mucosal lining hasalso been suggested (Charleston, 1965).The decreased nitrogen retention during the latterstages of the experiments may reflect the extent of bloodloss due to the adult parasite. Calculations based upon theestimated daily blood loss (Andrews, 1942; Clark, Kiesel &Goby, 1962) caused by the adult parasite show that a lambmay lose as much as 20 g of protein per day. This wouldcontribute considerably to a decreased nitrogen retentionquite apart from any direct effect which the parasite mayhave on the digestive process.The isolated decrease in dry matter digestibility cannotbe explained by these experiments.The anorexia described by Evans et al. (I963)for sheep infested with H. contortus was not a prominentresult of these experiments. A transient decrease in feedintake was nevertheless observed about 2 weeks after in-festation corresponding to the early decrease in both nitro-gen retention and body mass.These preliminary results require further investigation,especially with regard to the effect the parasite may haveon protein digestion. One problem with such experimentsis the difficulty in obtaining uniform levels of infestationfor comparative purposes.ANDREWS, J.S., 1942. Stomach worm (Haemonchus contortus) infection in lambs and its relation to gastric haemorrhageand general pathology. J. agric. Res. 65, 1.CHARLESTON, W.A.G., 1965. Pathogenesis of experimental haemonchosis in sheep, with special reference to the develop-ment of resistance. J. comp. Path. Therap. 75, 55.CHRISTIE, M.G., BRAMBELL, M.R. & MAPES, C.J., 1967. Effect of young Haemonchus contortus on abomasal pH insheep. Vet. Rec. 80, 207.CLARK, C.H., KIESEL, G.K. & GOBY, C.H., 1962. Measurements of blood loss caused by Haemonchus contortus in·fection in sheep. Am. J. vet. Res. 23, 977.CLARK, R., ORTLEPP, R.J., BOSMAN, S.W., LAURENCE, G.B., GROENEWALD, J.W. & QUIN, J.1., 1951. The in-fluence of nutritional level on verminosis in Merino lambs. Onderstepoort J. vet. Res. 25, 121.EVANS, J.V., BLUNT, M.H. & SOUTHCOTT, W.H., 1963. The effects of infection with Haemonchus contortus on the so-dium and potassium concentrations in the erythrocytes and plasma, in sheep of different haemoglobin types. Aust.J. agric. Res. 14, 549.HORAK, I.G. & CLARK, R., 1964. The pathological physiology of Ostertagia circumcincta infestation. Onderstepoort J. vet.Res. 31, 163.OWEN, N.C., 1968. The pathological physiology of haemonchosis in sheep. M. Med. Vet. (phys.). Thesis, lJniv. Pretoria.OWEN, N.C., 1971. Plasma and blood volume changes in sheep experimentally infested with Haemonchus contortus.Jl S. Afr. vet. med. Ass. 42, 9.OWEN, N.C., NEETHLING, L.P. & TERBLANCHE, H.M., 1971. Cyanocobalamin (Vit. B12) absorption in normal andHaemonchus contortus infested sheep. Jl S. Afr. vet. med. Ass. 42, 15.REINECKE, R.K., HORAK, I.G. & SNIJDERS, AJ., 1963. Techniques for testing anthelmintics against immature Oeso-phagostomum columbianum. Proc. Int. Conf Wid. Ass. Adv. vet. Parasit., Hanover, 1, 167.SHUMARD, R.F., BOLIN, D.W. & EVELETH, D.F., 1957. Physiological and nutritional changes in lambs infested withthe nematodes, Haemonchus contortus, Trichostrongylus colubriformis, and Nematodirus spathiger. Am. J. vet. Res.18, 330.VEGILIA, F., 1915. The anatomy and life history of the Haemonchus contortus (Rud.). Rep. vet. Res. Union S. Afr.3/4, 347.

Some nutritional aspects of haemonchosis in experimentally infested lambs

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Some nutritional aspects of haemonchosis in experimentally infested lambs

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