Indicators for internal parasitic infections in organic flocks: the diarrhoea score (Disco) proposal for lambs

J. Cabaret, V. Gonnord, J. Cortet, C. Sauvé, J. Ballet, H. Tournadre, M. Benoit

Abstract – A diarrhoea score was tested in lambs in organic flocks of semi-mountains regions in centre France. This score was related to the various internal parasites along the grazing season (Coccidia, then Moniezia and Strongyles, then Nematodirus and finally Strongyloides). It can be used on an individual basis for treatment decision or to monitor the internal parasitism of the flock. It should be evaluated in different climatic regions and coul be tested also in conventional farms. 

Introduction
Internal parasitism is a major  problem in meat sheep production. Conventional farming is not restricted in the use of anthelmintics and relies strongly on them for parasitic control. In organic farming their use is restricted and farmers should use them in conjunction with other control measures (among others, pasture management: Thamsborg et al, 1999). The ideal, as no fully efficient alternative drug is available, is then to use synthetic anthelmintics only for animals or  categories of animals highly infected  and in need of treatment for production and/or ethical grounds. This strategy for control of  internal parasites is well in the line of  organic farming, but can be proposed also in conventional farms The difficulty for farmers or veterinarians is that internal parasites (except the cestode Moniezia) are not easily seen and require laboratory examination.  Furthermore their effects are gradual and symptoms (diarrhoea, anaemia, ill thrift) might be recorded in many other ailments.  It has been shown in French organic meat sheep farms that internal parasitism is not always managed adequately (Cabaret, 2003) by farmers, although it can be under  control when laboratory resources (strongyle faecal egg counts) are available (Cabaret, 2004; Niezen et al, 1996). Organic meat sheep production can be economically sound (Benoit et al, 2003), although it implies much more that  simply  restrict anthelmintic treatments and requires many adaptations during conversion (Benoit et al, 2005). The instruments in the hand of the farmers are limited: weight gains or condition score, dag-score (based on diarrhoea marks on the back of lambs: 

J. Cabaret, V. Gonnord, J. Cortet, C. Sauvé, with INRA, IASP-213, 37380 Nouzilly France (cabaret@tours.inra.fr)
J. Ballet, H. Tournadre, M. Benoit, with  INRA, LEE, 63122 Saint Genès Champanelle France (marc.benoit@clermont.inra.fr)

Larsen et al, 1995) or Famacha© (an index of anaemia: van Wyk et Barth, 2002).
 Here we present a diarrhoea score-Disco   that can be used by farmers. We will answer to the following questions : is Disco i) repeatable within lambs, 2) related to strongyle faecal egg counts or worm infection ? related to other internal parasites (Strongyloides, Moniezia, Coccidia) ? and should we use Disco as a general flock indicator for treatment ?

MATERIAL AND METHODS

Two experimental farms (Redon-2 organic flocks and Orcival-one managed as organic and one conventional flock) participated in the elaboration of the diarrhoea score (Disco) from 1999 to 2005 (5 lambs in each flock/each month). The major strongyle nematodes in lambs are Teladorsagia circumcincta, Trichostrongylus axei in both sites.  The Redon site has also Cooperia  curticei in numbers whereas Trichostrongylus vitrinus were rather found in Orcival. Resistance to benzimidazoles was demonstrated in T. axei  and C. curticei and consequently levamisole was used for treatments. Due to the absence of Haemonchus contortus, a blood sucker, the Famacha© was not used
The score of  1 correspond to normal sheep faeces in pellets, 2 is for “soft” faeces (similar to cow pat) and 3 is for diarrhoea (semi-liquid faeces). These scores corresponds to 40, 26 and 16% dry-matter, respectively. Faecal strongyle egg or oocyst counts were performed on the lambs tested for Disco.

RESULTS

Repeatability of individual  diarrhoea scores:
The measure was performed once in August on 121 lambs 3 consecutive days. The Spearman rank correlation was 0.5 (highly significant) between days 1 and 2, 1 and 3 and 2 and 3. The monthly repeatability on the full season of pasture was not significant (0.05).

Individual diarrhoea score and strongyle faecal egg count:
Disco is not correlated to faecal egg counts when not corrected for dry-matter. As the faecal egg counts correspond to a concentration we estimated faecal egg counts per gram of dry-matter, but it remained insignificant (General linear model including season, year, flock as covariates: p=0.20). We selected in July 2002 5 lambs with Disco 3 and 5 lambs with Disco 1 (normal). At necropsy, the number of adults was much higher in the diarrhoea group (T.circumcincta X4, T. axei x5, Nematodirus x4). The difference was more important for larval stages of T. circumcincta  (x10) or Nematodirus (only present in diarrhoea group).
Diarrhoea score in relation to internal parasite dynamics:
The results are presented in Table 1. Individual Disco is  significantly related to Strongyle infection and Moniezia in Spring. Individual Disco is again related to strongyles in Autumn. It is related to Strongyloides  in Summer and Autumn.

Table 1: Correlations between individual diarrhoea score and internal parasites

	Spring	Summer	Autumn	
Digestive
Tract  strongyles	+ (p=0.08)	NS	+ 
(p=0.01)	
Nematodirus	?	NS	NS	
Strongyloides	NS	+ (p=0.04)	+ (p=0.09)	
Moniezia	+ (p=0.05)	NS	NS	

Disco as a flock indicator of internal parasitism:
We use the percentage of lambs with Disco 3 as an indicator for flock. It ranges from less than 5% (August-September) to 35% (April-May) of lambs in  the flock depending on month of sampling. In April May it was associated with Coccidia peak (140.000 to 160000 oocysts/g dry matter of faeces). The May-June high Disco 3 (diarrhoea in over 30% of lambs) was associated with Moniezia (45% of the lambs) and strongyles (2500 egg/g faeces dry-matter) infection. The score in July-August (20% is associated with Nematodirus peak (>200 egg/g faeces dry-matter).  A score of  20% with Disco 3 is found in October-November and is associated with Strongyloides.

DISCUSSION- CONCLUSION

The diarrhoea score was evaluated in meat sheep reared under a fairly continental climate (semi-mountains regions of centre of France). Thus strongyle species such as Haemonchus were not present. In our conditions there was no Fasciola liver fluke and internal parasitism was at low level compared with other farms in the same region. It is obvious that the diarrhoea score should be tested in other climatic environments.  Its use can also be proposed in conventional farms.
Individual Disco was a good indicator in relation to season to assess the necessity of individual treatment (targeted selective treatment). The interest was to encompass the main groups of internal parasites and thus the farmer may adapt the treatments when needed to the parasites  that affect lambs. However it is time consuming (and labour costly) and require facilities for sampling faeces from lambs. 
Disco as a flock indicator will be more acceptable in terms of work power management, as only a part of the flock need (10-15 lambs) to be sampled. It would then indicate when to treat and against which parasite. However the indication will stand for all the flock and then could result in the decision to treat all the lambs. 

Acknowledgement
This research was undertaken  with the « Pôle Scientifique Agriculture Biologique Massif Central» and was funded by FEOGA obj 5b Massif Central and CIAB (Comité Interne Agriculture Biologique de l’INRA).  Discussions with colleagues during the preparation of the European program Parasol helped to integrate the diarrhoea score within the frame work of other indicators for a global use in targeted selective treatment.

References

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