The Effects of Fascioliasis on Ewe Fertility

Br. vet. ]. (I 976) IJ2, s68

THE EFFECTS OF FASCIOLIASIS ON EWE FERTILITY Bv M. J. HoPE CAWDERY

The Agricultural Institute, Ballinamore, Co. Leitrim SUMMARY An inverse relationship was demonstrated between the pregnancy rate of ewes and the mortality rate due to fascioliasis in the same flock. It was also shown that therapy with fasciolacides (active against immature fluke) before mating improved the reproductive performance. It is concluded that fascioliasis has an adverse effect on conception andfor establishment of the foetus. INTRODUCTION It has been suggested (Hope Cawdery, I972 a, b) that infection with Fasciola hepatica reduces reproductive performance in ewes when parasitic invasion of the bile ducts (i.e. a crisis) coincides with mating and establishment of the foetus. As this effect is economically important, an attempt was made to substantiate the suggestion by two indirect methods: first, by therapeutically eliminating immature fluke before mating, whereby an improvement in fertility would provide circumstantial evidence to support the suggestion; second, by correlating the level of infection (as measured by mortality rate) with pregnancy rate. MATERIALS, METHODS AND RESULTS The first approach involved the use of drugs active against immature fluke. Two drugs, emetine hydrochloride (Grant & Jaggers, I969) and diamphenethide (Dickson, Harfenist & Kingsbury, I97I) have been described which have specific activity against immature fluke. Both these drugs were used to eliminate fluke before mating in the following experiment. Mature mountain blackface ewes from each of four flocks (A, B, C and D) were randomly allotted to one of three treatments. Treatment I

Basal therapy only, 2 ml of carbon tetrachloride (Injectable: N. V. Philips-Duphar, Amsterdam) injected subcutaneously every four weeks. Treatment II Basal therapy plus an oral dose of diamphenethide (Coriban: Burroughs Wellcome & Co., Berkhamstead, Herts.) ( 100 mgjkg) (a) 4 weeks before mating and (b) at the time of introduction of the rams.

THE EFFECTS OF FASCIOLIASIS ON EWE FERTILITY

s6g

Treatment III Basal therapy plus a subcutaneous injection of emetine hydrochloride (3 mg/kg) (a) 4 weeks before mating and (b) at the time of introduction of the ram. The following definitions have been used throughout this paper: All sheep dying during experiments were autopsied and deaths were attributed to fascioliasis if severe chronic liver damage or lesions of acute fascioliasis were found. The former corresponds to the liver damage described under Code 3 and 4 (Hope Cawdery & Donnelly, 1972). Macroscopically this includes extensive fibrosis of the left lobe and moderate fibrosis of the remainder of the liver. There is general thickening of the bile ducts and an overall enlargement of the liver. If these criteria were not met or if an alternative specific cause of death was identified, the death was attributed to 'other causes'. The mortality rate due to fascioliasis is defined as the ratio of the number of deaths caused by the disease between September and lambing (April) in each year to the number of ewes at risk during this period. 2. Ewes were defined as pregnant if they lambed or if there was a foetus in utero at post mortem. They were defined as barren only if they had been covered by the ram and had survived at least two months after the end of the mating period. At this stage the presence of a foetus in the uterus was unlikely to be missed at post mortem. The pregnancy rate is defined as the ratio of the number of pregnant ewes (dead or alive) to the number of ewes surviving at least two months after mating. The denominator in the calculation of pregnancy rate (i.e. the number of ewes surviving as defined above) therefore includes only those ewes which could have had an identifiable pregnancy. Similarly, the numerator includes all identified pregnancies irrespective of whether it was identified post mortem or by successful lambing. These provisions make the estimate of this rate independent of the concurrent mortality rate. Evidence that these flocks were exposed to fluke infection was based 1.

(i) on the identification of fluke eggs in faecal samples from all ewes (ii) on confirmation of fascioliasis by post mortem of dead ewes and (iii) in flock D, a high level of exposure before mating was demonstrated by the use of tracer sheep, the average intake being 1091 fluke from mid-May to mid-November. Due to the general uniformity of reclaimed peatland in this area, this indicates a high level of infection by F. hepatica to all sheep. The results of this trial are shown in Table I. There were no demonstrable,significant differences in mortality between flocks or between treatments. This is not surprising as this trial was not big enough to demonstrate such changes in the low level of mortality which was recorded. However, as both diamphenethide and emetine are highly effective fasciolacides, their inclusion in the treatment regime would probably result in reduced mortality rates. A larger trial or high mortality rates would probably be required to demonstrate statistically significant differences.

BRITISH VETERINARY JOURNAL, 132, 6 TABLE I PROPORTIONS OF PREGNANT EWES (NUMBER PREGNANT/NUMBER TREATED AND SURVIVING AT LEAST 2 MONTHS AFTER MATING) IN EACH FLOCK AND TREATMENT

Flock Treatment A CC1 4 CCI 4 + diamphenethide CCI 4 + emetine Mean

o·82 (g/11) 0'92 (12/13) o·85 (11/13) o·86

Mean

B

c

D

0'43 (3/7) 0'75 (6/8) 1·oo (8/8) 0'74

0'25 (2/8) o·5o (4/8) o·67 (6/g) 0'48

o·67 (6/g) 0'75 (6/8) o·88 (7/8) 0'76

0'57 0•76 o·84 0'73

There were significant differences in pregnancy rates both between treatment (P < o·o2) and between flocks (P < o·o1) by chi-square analysis. The treatment differences were reasonably consistent from flock to flock. Ewes treated for immature fluke with diamphenethide or emetine showed a significantly higher pregnancy rate (o·8o) than those treated with carbon tetrachloride alone (o·57). Although a slightly better rate followed emetine than diamphenethide treatment, a difference such as this would commonly occur when equally effective treatments were tested in an experiment of this size. It must be concluded that both treatments are equally effective. Further statistical analysis, using the logit transformation, was very kindly done by the referee and confirms these conclusions. To correlate mortality and pregnancy rates, records covering the period Ig66-1971 from five flocks were examined. These flocks had been exposed to infection with fluke while grazing on reclaimed blanket peat. Since these flocks had been the subject of experiments in the control of fascioliasis (including 4weekly carbon tetrachloride therapy to all ewes) and because of climatic differences between years, a range of flock mortality rates and pregnancy rates had been recorded. As cercarial shedding has been shown to occur from May to October by using tracer sheep (unpublished data), only the data from ewes present in each flock in June have been used in this study. The number of ewe observations in each category of a 3 by 3 table are shown in Table II for the whole period. DQring this time (1966-1971) the mortality rate due to fluke from September to April was 14·3%; of the deaths, 23 occurred before or within two months of mating i.e. up to December. Over the period January to April 19 deaths occurred in barren ewes while 20 deaths occurred in pregnant ewes. Thus, two thirds of the deaths caused by fascioliasis occurred after December. In the period January to April7·o% of the pregnant animals died of fascioliasis compared with 15·8% of the barren ewes. By the chi-square test this difference is significant (P < o·o1 ). Thus the mortality rate due to fluke in pregnant ewes was less than half the rate found in barren ewes.

THE EFFECTS OF FASCIOLIASIS ON EWE FERTILITY

57I

Further break-down of Table II to examine annual differences (Table III) shows that large differences only occurred in two seasons. However, in no year did the mortality in pregnant ewes exceed that of barren ewes despite the additional stress of pregnancy.

TABLE II NUMBER OF EWES IN THE SURVEY AND THE DEATH RATES IN PREGNANT AND BARREN EWES

Survival state Period

Fertility state

Pregnant

Jan. to April

Barren Sept. to Dec.

U nclassifiable* Total

Alive

Dead (fluke)

200

20

98

0 358

Dead (other causes)

Total

6 (2·I %)

286

(7·0 % ) I9 (Iy8%)

3 (2 "5 %)

I20

23

5

28

62

I4

434

(I4"3%)

* Unclassifiable due to death before mating or in very early pregnancy.

TABLE III THE ANNUAL MORTALITY RATE DUE TO FASCIOLIASIS IN PREGNANT AND BARREN EWES

rear I966j67 I967/68 I968j6g 1969/70 I970/71

Pregnant

Barren

%

%

9"8 20"0 0 6·2

10"3 24"0 0 I6·o I7·6

4"4

On the assumption that flock mortality is a measure of the level of infection to which a flock is exposed, an examination of the correlation between level of infection (as measured by mortality rate) and fertility (as measured by the pregnancy rate) can be made. The breakdown of the data in terms of years, flocks, survival, death and pregnancy is shown in Table IV. The pregnancy and mortality rates were calculated for each flock in each year and provided a pair of observations. Twenty one such paired observations were obtained. The results were analysed by Spearman's rank correlation test. The correlation

TABLE IV PREGNANCY AND MORTALITY DATA TOGETHER WITH THE RA NKIN GS FOR FLOCK FERTILITY ( AS MEAS URED BY TH E P REGN ANCY RATE OF EWE S SURVIVIN G TWO MO NT HS AFTER MATI NG) AND LEVEL OF INFECTION WITH F. hepat ica (AS MEAS URED BY THE FLOCK MORTALITY RAT E CAUSED BY THE PARASITE I N FLOCKS DURING TH E PERIOD I g66 - I 9 7 I )

(Jl

..... ~

No. of Ewes Alive Year

66/67

67/68

68/6g

6gf 70

70/ 71

Flock

2 3 4 I 2 3 4 I 2 3 4 I 2 3 4 5 I

2 3 4 5

Pregnant

Dead Barren

8 I6 13

II 7 8

9 I3 3 II 12 20 r8 I8

4 4 8 3

14 13 20 14 I5 14 6 7 3 I3

5 2 4 6 4 0 5 12 9 2

260

g8

I

0 I 2

Pregnant 0

FL

I

I

Barren

Pregnancy rate Unclass

FL

0

FL

2

I

I

2

2

3 I

4

2

2 4 2 2

I

5

0

2

2

5 I 2 I

2 I 4 I

I I

I

I 2 3

I I 6

20

3

I9

Mortality rate

I I 6 5

No.

%

Rank

No.

%

Rank

11 / 23 16/ 23 I5/25 I2 /20 I5/2 I 3/ I I I6/2I

48 70 6o

18 I3 I5 I6 I2 20 9"5

19 I5 22

I4 I3 17 20 9 I8 I9

13/ 14 22 /22 19/20 18j2o

93 100 95 go

5/26 4/27 6/ 27 9/24 1/21 5/ I7 7/2 I 0 0 0 0

14/2 1 13/ 15 20/24 18/25 16j2 1

67 87 83 72 76 IOO 54 32 25 87

I4/ 13 7/ 13 7/22 4/ 16 I3 / I5

57 71 27 76

4 1"5 3 5 I4 6·5 8 II 9"5 1" 5

I7 19 21 6

2/ 2I 0 0 5/25 2/2 1 0 3/ I4 3/23 10/22 0

38 5 29 33 0 0 0 0 10 0 0 20 10 0 21 13 46 0

4"5 4"5 4"5 4"5 10·5 4"5 4"5 15 10"5 4 "5 I6 12 2I 4"5

23

rs = o·83 N= 21: P < o·or 0-Death due to causes other than fascioliasis. FL-Death due to fas cioliasis. Unclass-Ewes dying b efore pregnancy classification possible. Therefore excluded from calculation of pregnancy rate.

co

~ ......

...,...... rFl

::r:

<

...,

~ ~

~ ......

z > ~

....::

t....,

0

c:: ~

z >

r M

""~"" 0>

THE EFFECTS OF FASCIOLIASIS ON EWE FERTILITY

573

co-efficient (r. = -o·83) was highly significant (P < o·ooi), suggesting an inverse relationship between the mortality rate due to F. hepatica and the pregnancy rate in ewes. The estimate of pregnancy rate assumes that the fertility of ewes that died during September-December was the same as the fertility of the survivors. As there is a suggestion that barren ewes have a higher mortality rate than pregnant ewes, the alternative extreme assumptions, namely that all ewes dying in the period September to December were either all barren or all pregnant, were examined. The effect on the correlation coefficient is negligible as shown below. I. All September-December deaths classified as pregnant All September-December deaths classified as barren 3· Ewes dying in September-December excluded as in text above 2.

r. = -o·8I r. = -o·84 r. = -o ·83

Within the context of the available data, the assumption regarding the fertility of ewes dying offascioliasis from September to December does not appear to be important. However, in other circumstances, where a large proportion of ewes died before January this aspect could be of considerable importance. If the analysis is restricted to those ewes surviving until January the correlation coefficient is still significant (r. = -o·6I; P < o·oi). From this it would appear that the null hypothesis which proposes that there is no correlation between mortality rates and pregnancy rates is unlikely to be true. The results therefore suggest an inverse relationship between mortality rates and pregnancy rates; that is, high mortality rates due to fascioliasis tend to be associated with low pregnancy rates and vice versa.

DISCUSSION

The prior use of proven drugs, active against immature fluke, by preventing a disease crisis at mating, resulted in a significant improvement in pregnancy rate in treated ewes. Apart from confirming the clinical value of this type of therapy, this fact provides further evidence to support the suggestion of Hope Cawdery (I 972 a, b,) that fluke infection affects conception and/or establishment of the foetus in early pregnancy. Such effects may be explained by the liver damage and blood loss caused by the parasite. The pathological effects of infection would lead to physiological and nutritional stress, which could be viewed as the reverse of pre-mating 'flushing'. This suggested an examination of experimental flock records over a number of years. One approach to this is to set up the null hypothesis that both pregnant and barren ewes are two subsets of one main set which is subject to one level of infection. It is assumed that the stress of pregnancy has no effect, or that if it had an effect, it would increase rather than decrease the mortality rate of pregnant ewes. If pregnant and barren ewes are merely two samples of the one population (in terms oflevel of infection) then the mortality rate in each sample should not be significantly different on average, providing that the assumption that the mortality rate is correlated with level of infection is true. Despite the possible

574

BRITISH VETERINARY JOURNAL, 132, 6

effects of pregnancy increasing the mortality rate, there was a significant difference between the two mortality rates. This suggests that the mortality rates, and consequently, the levels of infection, were different. Further analysis (Table III) does not confirm this suggestion but this may be in part due to smaller groups and in part due to the balance between survival without a lamb or death with the extra stress of carrying the lamb. When these annual results are taken in conjunction with the variability and timing of metacercarial pick-up it is likely that any differences would be small and not readily demonstrable. Indeed, if one accepts the assumptions that the stresses of pregnancy increase susceptibility to disease and that the disease does not affect fertility, then it could be postulated that the pregnant ewes would have, on average, a higher mortality rate than barren ewes. The results actually suggest a contrary trend. However, in general terms, the intention was to show that fascioliasis adversely affects fertility over years and flocks and the analysis of the overall data supports this suggestion. To add further support to the hypothesis that infection with fascioliasis affects fertility in ewes, the flock data was also analysed for correlation between the mortality rate and pregnancy rate using Spearman's rank correlation test. The main assumption is that ewes surviving until January are a valid estimate of the overall flock fertility. The result of this analysis is significant (P < o·oi). Further analysis, using alternative extreme assumptions does not alter this result; it remains significant. Thus the analysis suggests that mortality rate, due to fascioliasis, and pregnancy rate are not mutually independent but that there is a significant tendency for the lower mortality rates to be associated with higher pregnancy rates and vice versa. If the assumption is made that mortality rates are related to levels of infection, it follows that there will be a tendency for high levels of infection to be associated with low pregnancy rates; and conversely. While mortality rate is not an ideal measure of infection level, the assumption that a relationship exists between the two is commonly made. It is the basis of many biological titrations. In this case it was the only possible measure as faecal egg counts are not particularly useful in this respect when the animals are regularly treated. The data presented above suggest an important relationship between mortality rate due to fascioliasis (and, consequently, the level of infection) and pregnancy rate in ewes. In normal circumstances, with mortality rates in the range of o-10%, the effect is unlikely to be noticed and would be difficult to demonstrate. It is only in a situation of continuous high level infection such as exists on reclaimed blanket peat, that such a relationship would become apparent. Nevertheless, the effect on ewe production would occur wherever ewes are exposed to infection with F. hepatica, though the degree of reduction might vary if the distribution of fluke numbers within sheep differed from that found under conditions pertaining on reclaimed peat (Hope Cawdery & Moran, I 971). Reduced lambing rates, resulting both from low fertility and ewe deaths, seriously increase the financial loss usually attributed to the disease on the basis of overt losses. This further emphasizes the economic need for effective, planned control measures against this parasite.

THE EFFECTS OF FASCIOLIASIS ON EWE FERTILITY

575

ACKNOWLEDGEMENTS

I am indebted to the Director, The Agricultural Institute, for permission to publish. I am also very appreciative of the assistance given to me by my colleagues, especially Dr D. Harrington, Dr N. E. Downey and Mr J. Mulqueen in the preparation of the manuscript. I would also like to express my sincere thanks to the referee for his very helpful comments. REFERENCES

G., HARFENIST, M. & KINGSBURY, P. A. (1971 ). Br. vet. ]. 127, xl. GRANT, M. S. & jAGGERS, G. E. ( 1969). Res. vet. Sc. 10, 197. HoPE CAWDERY, M. J. (1972a). Jr. vet. ]. 26, 99· HoPE CAWDERY, M. J. (1972b). Jr. vet.]. 26, 118. HoPE CAWDERY, M.J. & MoRAN, M.A. (1971 ). Br. vet. ] . 127, 118. HoPE CAWDERY, M. J. & DoNNELLY, W. (1972). Jr. vet.]., 26, 163. DICKSON,

(Accepted for publicatio11 11 December 1975)