Economic Significance of Fasciola Hepatica Infestation of Beef Cattle a Definition Study based on Field Trial and Grazier Questionnaire

Transcription

1 Economic Significance of Fasciola Hepatica Infestation of Beef Cattle a Definition Study based on Field Trial and Grazier Questionnaire B. F. Chick Colin Blumer District Veterinary Laboratory, Private Mailbag, Armidale, N.S.W. Summary A production trial is described in which losses due to subclinical Fasciola hepatica infestations are defined. From this field trial work, and with the aid of a limited producer survey, direct costs and indirect losses due to Fasciola hepatica infection in weaner beef cattle are estimated. It is concluded that even in regions of low incidence of fascioliasis, regular control measures should be undertaken in weaner cattle. Severe clinical disease due to liver fluke ( Fasciola hepatica) is a minor problem in beef cattle in Australia run under open range conditions (Seddon, 1967). However the potential significance of subclinical infections is much more important (Seddon, 1967; Gordon, 1955; Chick, 1974). In high infections causing either mortality or obvious production losses the desirability and cost of treatment becomes a secondary factor, however in subclinical fascioliasis, particularly in cattle which have a degree of resistance, significant production losses may be experienced in the absence of overt clinical signs. Sewell (1966) demonstrated that there was a depression in weight gain of cattle infected with Fasciola gigantica, and that this reduction was related to parasite numbers. A number of other authors have shown similar effects with Fasciola hepatica when measuring other production attributes, such as milk production (Ross, 1970) feed conversion efficiency (Hope-Cawdrey and Conway, 1971) and composition and quality of milk (Norman et al., 1976). It has also been shown that cattle given a single dose of 1000 metacercariae showed a declining erythrocyte count for eighteen weeks. This low count persisted for six to eight weeks and was followed by a slow fluctuating rise to normal after eight months (Morrill and Shaw, 1942). If during this period of lowered erythrocyte values there was a concurrent stress (say nutritional) the fluke infected cattle may show a more rapid loss in body weight than uninfected cattle. The economic significance of subclinical liver fluke infection may be divided into two broad categories: 1. Direct costs, made up of costs of drenches, labour, and condemnations of livers from abattoirs. 2. Indirect losses: those production losses which include poor growth rate, delayed finishing, and decreased resistance to physiological and environmental stress. In this study direct costs were estimated with the aid of a questionnaire, indirect losses by a limited field trial. Questionnaire A 'mail in' type questionnaire was sent to 140 cattle producers in the Armidale 377

2 Pastures Protection Board area. Recipients were selected at random from the total ratepayers, the number sampled representing 6 per cent of the total number in the district. From these replies it was shown that 50 per cent of graziers who recognised that they had liver fluke on their properties felt that this disease caused subclinical production losses and took some regular control action. The remainder of operators, in spite of recognising the presence of the disease either took no action or only took action if clinical signs were evident. From the questionnaire we were able to estimate direct costs. In allowing for labour costs 90 per cent of respondents who regularly drenched for liver fluke did so in association with a second essential management practice. Because of this the marginal cost of labour in administering the drench must be close to zero. For our study we costed labour as zero. The average cost of the various control programs undertaken by those operators who undertook regular control action was $2.40 per head. Field Trial Experimental work was designed to determine the effect of two superimposed artificial levels of infection on a low grade natural infection, using Hereford steers. The experimental period was between the twelfth and eighteenth months inclusive and cattle were maintained under open range conditions. Trial conditions were replicated under two levels of nutrition. The experimental work was carried out 7 miles east of Glen Innes on the New England Tablelands. The soil type is fine granite with an undulating topography and average altitude of 1100 metres. Suitable habitats for Lymnaea tomentosa are throughout the property. Experimental Design Forty-eight Hereford steers of even age and body weight were divided into six groups of eight on a stratified body weight basis. Three of the six groups were allocated to an ad lib nutritional plane and grazed as a single unit. The remaining three groups were allocated to a restricted nutritional plane and grazed as a second unit. Within each grazing unit the three groups were treated similarly. Group 1. Artificially infected with 1200 metacercariae of Fasciola hepatica given by intraruminal injection in three equal doses of 400 at two-weekly intervals. Group 2. Artificially infected with 600 metacercariae of Fasciola hepatica given by intraruminal injection in three equal doses of 200 at two-weekly intervals. Group 3. Natural infection of Fasciola hepatica. Cattle in the ad lib nutritional plane group were allowed unrestricted access to improved pastures, completing the trial period with an average stocking rate of 3.54 beasts/hectare. Cattle in the restricted nutritional plane group were limited to smaller paddocks and completed the trial with an average stocking rate of 4.93 beasts/hectare. Sampling and treatment All animals were faecal sampled and weighed monthly for the duration of the trial. A broad spectrum anthelmintic (Nilverm*) was given at the commencement of the trial and thence repeated monthly throughout, to limit the effect of nematode infections. * Nilverm, ICI Australia Limited, 1 Nicholson Street, Melbourne, Victoria 378

3 Slaughter Cattle were selected on a random body weight basis at the commencement for slaughter at predetermined times throughout the trial's duration. At slaughter all carcasses were weighed. Livers and abomasums were removed intact. All livers were weighed and total liver fluke present counted and measured by standard methods. Statistical Analysis 1. Conventional analysis of variance was used to analyse differences between groups in total Fasciola hepatica numbers, and the effect of nutrition on these values. Duncan's multiple range test for differences between means was used in interpretation. Fluke numbers were analysed over two kill periods: (a) Cattle killed on week 12 post infection (b) Cattle killed weeks post infection. 2. Repeated measures covariance analysis for live weights and means was used in analysing body weight changes. Two models were examined: (a) Level of fluke infection and the interaction nutrition by fluke infection at 2 degrees of freedom. (b) Level of fluke infection and the interaction nutrition by fluke infection split into single degrees of freedom. Results Overall the experimental work showed that body weight changes were significantly affected (P <0.05) by concurrent liver fluke infection, particularly in the first twelve weeks post infection (P <0.01). During this initial twelve-week period there was also a significant (P ) interaction between the effects of nutrition and fluke on body weight changes, supporting the hypothesis that the overall effect of fluke infection is potentiated if there is a concurrent nutritional stress. This effect was not maintained beyond the initial twelve-week period. Level of Fasciola hepatica infection A summary of total fluke counts from all animals is given in Table 1 along with slaughter times and numbers of cattle slaughtered,. On analysis there was no significant difference between levels of nutrition, however there were significant differences within nutritional groups, between levels of artificial infection. Maximum numbers of parasites were recovered between twelve and sixteen weeks post infection. Body weight changes The daily weight gains for each treatment split into the two periods of the analysis are shown in Table 2. Body weight gains of up to 1.64 kg/day were achieved in the first twelve-week period and up to 1.46 kg/day overall. Over the entire trial period, superimposed artificial infection rate of 1200 metacercariae depressed growth rate by 13.9 per cent and 600 metacercariae depressed growth rate by 11.7 per cent when compared to the naturally infected control group. These findings are in agreement with previously published estimates of cost of productivity losses. Ross (1970) states that low grade infections of around 100 fluke result in an 8 per cent loss in productivity, moderate infections of around fluke 379

4 in a 16 per cent loss and heavy infections of 500 or more fluke in a 23 + per cent loss in production. If these estimates are correct then a simple graph relationship can be drawn depicting percentage productivity decrease to total fluke recovered per animal (See Figure 1). From the graph a simple break even budget strategy may be initiated. There is a point above which, once infection rates rise, the resultant productivity decrease is sufficient to warrant the cost of control measures. Obviously this point varies dependent on cost of drench, labour and the current market price for cattle. In the case of our survey and the limited experimental production data in New England, this point would appear to be when low numbers of Fasciola hepatica are present (perhaps as low as per head). Table 1: Average numbers of fasciola hepatica recovered per head in each analysis period with statistical interpretations Period 1 Period 2 Slaughtered Week 12 Slaughtered Weeks Group 1 258a 144a Ad Lib Group 2 222a 69b Grazing Group 3 29b 421 Group I 265a 139a Restricted Group 2 180a 133. Grazing Group 3 19b 27b Fasciola hepatica burdens in the same column bearing different subscripts are significantly different (P 0.01) Table 2: Body weight changes with standard deviations (kg) AD LIB NUTRITION 3.54 beasts/hectare Group 1 Group 2 Group 3 RESTRICTED NUTRITION 4.39 beasts/hectare Group 1 Group 2 Group 3 Initial body weight Body weight week 12 Final body weight week 32 Daily Body weight gain 0-12 weeks Daily body weight gain weeks Depression in body weight gain to natural infected controls 0-32 weeks ±33 ±34 ± ±33 ±26 ± ± 28 ± 32 ± 35 ±28 ±34 ± % 19.9% 14.2% 3.5% 380

5 Figure 1 Total Fluke recovered / Productivity decrease" 20 15_ I I I Total Fluke Recovered/Animal "Adapted from ROSS (1970) Figure 2 Fluke infection Body weight changes (kg). 425 _ rn a) 400 _ 375 _ _ _ Nil Metacercariae 600 Metacercariae 120b Metacercariae 275 _ Sampling & Weighing Dates

6 Acknowledgment This study was supported in part by an Australian Meat Research Committee grant. REFERENCES Chick, B. F. (1974) The economic significance of liver fluke infestation in beef cattle- --an area study. Dept Ag. Econs. dissertation, University of New England. Gordon, H. McL. (1955) Some aspects of Fascioliasis, Aust. Vet. J. 31 p Morrill, D. R. and Shaw, J. N. (1942) cited by H.McL. Gordon, Aust. Vet. J. 31 p Ross, J. G. (1970) The economics of Fasciola hepatica infection in cattle Br. Vet. J. 126 p. xiii. Seddon, H. R. (1967) Helminth Infestations. Commonwealth of Australia, Dept of Health Service Publications (Veterinary Hygiene) No. 5. Sewell, M. M. H. (1966) The pathogenesis of Fascioliasis Vet. Rec. 78 p