Abstract:
The Effect of Worm Parasites on the Productivity of Sheep H. McL. G ORDON * Summary Observations are reported which illustrate the effects of helminthosis on appetite, growth and fattening, wool quality and quantity and milk production. In addition helminthosis may cause prolonged unthriftiness as well as acute disease. The implications of helminthosis on animal production are discussed with emphasis on the need for more data and the necessity to control or allow for its effects in trials with grazing sheep. Techniques for measuring the effects of worm parasites on production are also discussed. INTRODUCTION Death is the obvious and severe manifestation of helminthosis, but in the aggregate serious outbreaks with high mortality are uncommon. The more insidious effects of lighter infestations on health and productivity are not always clinically apparent and may not be recognised unless weight gains and wool production are measured. An accurate diagnosis usually requires an examination of material at a laboratory. Some results of laboratory and field trials are presented to emphasise the ways in which helminths may harm their sheep host and to show the extent of the effects on productivity. TABLE I. *Division of Animal Health and Production, Animal Health Laboratory, Sydney, N. S. W. C.S.I.R.O., McMaster 59 O BSERV A TIONS A ND EXP ERIMEN TS (i) Appetite .-The effects of trichostrongylosis on appetite were illustrated by Andrews (1939)) Gordon (1950) and Gibson (1955). Some further results are shown in Table 1. A decrease of about 50 per cent. in food intake occurred within six weeks after sheep were given a single dose of 50,000 Trichostrongylus colubtif ormis larvae. The effects of oesophagostomosis are shown in Figure I. Food intake decreased from over 2.5 lb. daily to 1 lb. within a month of the administration of 4,900 Oesophagostomum columbianum larvae. Pre-infestation food intake was not regained for almost a year. . (ii) Growth and Fattening .-The effects of trichostrongylosis on weight gains by two sheep are shown in Figure 2. Sheep B4' 75 developed a strong resistance and suffered only minor interference with weight gains while B477, which remained susceptible, was unthrifty for over nine months. A somewhat similar result is seen in Figure 3, which also illustrates prolonged effects. The protracted effects of oesophagostomosis are seen in Figure 4, which shows loss of weight beginning within the first few weeks and persisting for over 300 days. Sarles (1944) recorded similar results and illustrated differences in carcasses and rib chops between control and infested sheep. (iii) Wool Quality and Quantity .-In a laboratory trial Carter et al. (1946) found that with sheep given moderate infestations with T. colubriformis the amount of wool produced dropped to 40 per cent. of that with worm-free controls. The food intake of both groups was maintained at the same level. In another trial a group of 14 sheep were infested with T . eolubriformb during their second year of life and with Oe. columbiawum during their third year. The effects of the latter parasite 60 FIG. 2-The effect of trichostrongylosis on body weight in sheep. the same age. Nos. I and 2 were dosed with larvae when 5 months and again when 7 months old. No. 1 remained susceptible. No. 2 developed resistance. No. 3 was a worm-free control. When the photograph was taken the sheep were 15 months old. Nos. 1 and 2 had thrown off their infestations but there was a prolonged effect in No. 1. The body weights at this time were:No. 1 60 lb. No. 2 117 lb. No. 3 110 lb. Weight gains from 3 months of age to 15 months of age were:No. 1 16 lb. No. 2 75 lb. No. 3 70 lb, FIG. 3-These three sheep are Trichostrongylus colubriformis on body weight are shown in Figure 4. The effects of both infestations on wool growth is shown in Table II. The quantity of wool was reduced in infested sheep and its quality was impaired especially in the third year when most fleeces were tender or had a ' break' in the fibre. Sarles (1944) has published illustrations of the effects of oesophagostomosis on wool growth and quality. 61 TABLE II. Effect of Trichostrolngylosis and Oesophagost' omosis Greasy Wool Weights. Sheep shorn at 1, 2 *and 3 years old. Between first and second shelaring sheep were infested with Trichostrongylus colubriformis and between the secolnld and third shearing they were infested with Oesophagostomum columbianum. on FIG. 4-The effect of oesophagostomosis on body weight. In some trials in Tasmania, Clunies Ross and Graham (1932, 1933) and Clunies Ross et al. (1937) recorded increased wool production and a reduced incidence of tender fleeces in sheep treated to control worm infestation. A comparison of wool growth between treated and control sheep in the New England district of N.S.W. is shown in Table III. There were two groups of sheep, 8 months of age, one group (A) consisted of 30, and one (B) of 60 sheep. Sheep in group A were run continuously in the same 30 acre paddock for two years. Sheep in group B were rotationally grazed through two 30 acre paddocks, spending 3 weeks in each while the other was spelled. Each group was divided into sub-groups, one of which was not drenched, while the other sub-group was treated with phenothiazine at intervals determined by epidemiological studies. 62 TABLE III. Effects of Treatment to Control Worm Infestation on IChanges in Body Wei,g;ht atnd Wool Production. The number of sheep in the groups was small, but the results illustrate several points:1. The effects of helminth infestations vary greatly from year to year. 2. In treated sheep there was an increase in fleece weight from 1942 to 1943 whereas in untreated sheep there was either a decline (0.25 lb. for B) or a very small increase (0.13 lb. for A). Some observations made in Western Australia are recorded in Tables IV and V. TABLE IV. Effects of Control of Worm Infestation on Wlool Production -and Quality. 20 weaners in each group each year. Greasy fleece weight (lb) Year Treated Controls Sheep with tender fleece, per cent. Treated Controls 1952 . . . . . . . . 1953 . . . . . . . . 1954 . . . . . . . . 11.25 13.3 14.4 9.0 11.9 15.3 50 90* Not recorded Not recorded *Many showed a distinct 'break' in the fibre. 63 \ 64 The results illustrate a number of aspects of the effects of helminthosis on wool production and quality. 1. In a year when infestations were severe (e.g. 1952, 1953 in Table IV, and 1955 in Table V) the effects on fleece weight may be very great, and conversely in years when infestations were light, as in 1954 and 1956, there is little or no effect. 2. In addition to producing less wool, the effects of malnutrition in causing tenderness and ' break' in the fibre may be aggravated in infested sheep. 3. Selective control of C. ovina by monthly drenching with 1:8 dihydroxyanthraquinone suggested that this parasite was of particular importance as a contributing cause of lowered wool production and quality. (iv) Milk Production.- The only figures available are those recorded by Gordon (1950). The milk yield of a ewe declined from 50 A. oz. daily to 11 fl. oz. within 20 days after the administration of 12,000 Haemonchus contortus larvae and returned to 29 A. oz. 20 days after treatment with phenothiazine. The effects of anaemia due to blood sucking parasites on milk yield and thus on the growth of the lamb may be considerable. (v) ProLonged Efec ts on, Thriftiness.-Some illustrations of prolonged effects have already been given in Figure 2 to 4. Further examples are provided in Figures 5 to 7, which illustrate some aspects bf trichostrongylosis. I. The effects may be prolonged and can cause unthriftiness lasting many months (Figs. 5, 6, 7). FIG. 5-The prolonged unthriftiness of trichostrongylosis. 2. Recovery may be prolonged for some weeks after removal of worms by treatment (Fig. 5). 3. Sheep may be unthrifty due to infestations with worms which do not produce eggs, and whose presence cannot be detected by faecal examinations (Fig. 6). 4. Spontaneous recovery often takes place about 90-100 days after an infestation was established (Fig. 7). These recoveries may give a false impression of the effects of treatment or management in controlling infestations. Unpublished work (Stewart and Gordon) suggests that this type of recovery is probably a manifestation of immunity, and that suppression of egg production is 65 FIG. 6-The prolonged effects of trichostrongylosis, including those of nonegg laying worms. D-Dosed with larvae. FIG. 7-The effect of trichostrongylosis produced by non-egg laying worms and spontaneous recovery. D-Dosed with larvae. also a manifestation of immunity in trichostrongylosis as in many other helminthoses (Chandler, 1953). Sheep that recover, or harbour worms that do not produce eggs, are not necessarily resistant to reinfestation (Fig. 6). Usually, however, most sheep that recover from trichostrongylosis are resistant to challenge doses of larvae (Stewart and Gordon, 1953). Prolonged infestations may have permanent adverse effects on growth and conformation. Some weaners brought to the McMaster Laboratory from the field after suffering severe infestations with mixed infestations, chiefly Trichos bong ylus spp., made poor weight gains and remained unthrifty for long periods after the worms were removed, and even when two years old still resembled weaners in size and conformation. Spedding (1956) has recorded body measurements which confirm these observations. He showed that there may be differential effects according to the age when the lambs are infested. Heavy infestations in early life may reduce bone growth and cause permanent stunting, while infestations when 3 to 4 months old affect chiefly muscle growth. Spedding (1954) and Gibson (1955) have shown that infested sheep do not make up their 10~s of productivity. . 66 (vi) Acute Effeets.- Outbreaks of helminthosis may be accompanied by considerable mortality. Severe mortalities often follow experimental infestations. On one occasion 35 of 99 sheep died within four weeks after a dose of 60,000 T. colubriformis larvae and in a current trial 12 of 40 sheep have died within 6 weeks after a dose of 50,000 larvae. Some of those sheep, which were 9 months old, died within three weeks after the dose of larvae, often before there had been much loss of weight. In outbreaks of haemonchosis severe mortalities are not unusual. During the course of epidemiological trials in northern N.S.W. in 1945-46 deaths from naturally acquired infestations ranged from 19 to 64 per cent. in four flocks of untreated weaners. I MPLICATIONS OF HELMINTHOSIS IN A NIMAL P RODUCTION There is need for further work with special reference to (I) changes in epidemiology due to changes in husbandry, (2) the effects of immature worms, (3) thriftiness and milk production and (4) infestations in fat lambs. In all trials with grazing sheep it is essential to control or to make allowance for the effects of helminthosis. The use of adult sheep, the inclusion of drenched and control groups and observations on grazing habits may assist in overcoming or measuring these effects. The more elaborate work of Spedding (1954, 1956)) who raised lambs worm-free by folding over spelled pastures, is an ideal which may not be as impracticable as it annears. His technique will have many applications in studies on intensive grazing. The collection of faeces in bags is a method for preventing contamination of pastures with worm eggs. DISCUSSION Helminthosis is a . common contributing cause of unthriftiness. Some of the symptoms of helminthosis are not readily distinguished from those of nutritional origin e.g. loss of appetite as in cobalt deficiency or with unpalatable feed (Clarke and Filmer, 1956) or diarrhoea due to lush growth of pasture or grazing crop, or to the ingestion of certain weeds such as Capeweed and Stinkwort. J. H. Whitlock (1949) has advocated a differentiation between primary and secondary helminthosis. Haemonchosis is generally accepted as a primary helminthosis, because deaths may occur from anaemia even in fat, thriving sheep on an adequate diet. Trichostrongylosis is often considered a secondary helminthosis, because it is commonly associated with malnutrition, and some consider that clinical trichostrongylosis does not occur unless sheep are suffering malnutrition. However, the pronounced loss of appetite seen in trichostrongylosis and in oesophagostomosis suggests some primary effect. Some of the confusion on the influence of nutrition may be resolved by current experiments at the McMaster Laboratory and by the comment by Stewart and Gordon (1953) that ' it might well be that when good nutritive conditions prevail, the development of larvae is also favoured, whereas, when poor nutritive conditions prevail, relatively few infective larvae are available to the sheep; sheep which ingest few larvae during their early life have less opportunity to develop an immunity than those which ingest more larvae under more favourable conditions' . It is difficult to obtain precise figures for the measurement of parasitic damage. Spindler (1947) found that control, worm-free pigs gained 0.79 lb. per day for 126 days. One pig harbouring 2 specimens of Ascaris suis gained 0.72 lb., one with 20 worms gained 0.47 lb., one with 40 worms gained 0.39 lb. and one with 100 worms made no gain in this period. It appeared that each worm reduced weight gain by about I lb. before the pig reached 5 months of age. 67 Boughton (1955) has assembled a good deal of data from work in U.S.A. and has, as far as possible, expressed the effects of the parasites as monetary loss to owner and industry. There are many ways in which parasites cause reduced productivity, but the precise ways in which the host' tissues are damaged s are not well understood. Interference with digestibility of nutrients by infested sheep has been recorded by a number of authors whose work is reviewed by Andrews et al. (1944)) Franklin et a2. (1946)) Spedding (1956) and Shumard et al. (1957). There is not complete agreement on the findings of the various authors, which is not surprising when one considers that they worked with different species of nematodes at different levels of infestation, and in some cases with mixed infestations. However, it is clear that the digestibility of protein, minerals and crude fibre may all be impaired. These effects, added to those of loss of appetite and the occurrence of diarrhoea, are sufficient to stress the role of helminthosis in unthriftiness. The examples of the effects of helminthosi .s in sheep have been given above with the following objects:I. To emphasise the importance of parasitic diseases as sources of economic loss. 2. To serve as a warning that in almost all field trials with grazing animals it is essential to recognise that parasitic infestations may interfere with the course of the trial and the interpretation of results. 3. To set down some of the techniques which might be adopted to measure and counter the effects of infestation. Andrews, J. S. (1939) .-7. agric. Res. 58: 761 . Andrews, J. S., Kauffman, W., and Davis, R. E. (1944) .-Amer. J. vet. Res. 5 : 22. Boughton, D. C. (1955) .-Advanc. Vet Sci. 2: 380. Carter, H. B., Franklin, M. C., and Gordon, H. McL. (1946) .-J. Coun. Sci. Industr. Res. Aust. 19: 61. Chandler, A. C. (1953).-J. Egypt. Med. Ass. 36: 811. Clarke, E. A., and Filmer, D. B. (1956).-N.Z. J. Agric. 92: 115. Clunies Ross, I., and Graham, N. P. H. (1932) .-J. Coun. Sci. Industr. Res. Aust. 5: 31. Clunies Ross, I., and Graham, N. P. H. (1933) .-7. Coum. Sci. Indust/r. Res. Aust. 6: 191 . Clunies Ross, I., Chamberlain, W. E., and Turner, H. N. (1937) .J. Coun. Sci. Industr. Res. 10: 313. Gibson, T. E. (1955) .-J. camp. Path. 65: 317. Franklin, M. C., Gordon, H. McL., and McGregor, C. H. (1946) .J. Coun. Sci. Industr. Res. Aust. 19 : 46. Gordon, H. McL. (1950) .-Aust. vet. J. 26: 46. 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