Date Published: May 13, 2011
Publisher: BioMed Central
Author(s): Atle VM Domke, Christophe Chartier, Bjørn Gjerde, Nils Leine, Synnøve Vatn, Olav Østerås, Snorre Stuen.
Anthelmintic treatment is the most common way of controlling nematode infections in ruminants. However, several countries have reported anthelmintic resistance (AR), representing a limitation for sustainable small ruminant production. The knowledge regarding worm control management represents a baseline to develop a guideline for preventing AR. The aim of the present study was therefore to improve our knowledge about the worm control practices in small ruminant flocks in Norway.
A questionnaire survey regarding worm control practices was performed in small ruminant flocks in Norway. Flocks were selected from the three main areas of small ruminant farming, i.e. the coastal, inland and northern areas. A total of 825 questionnaires, comprising 587 sheep flocks (return rate of 51.3%) and 238 goat flocks (52.6%) were included.
The results indicated that visual appraisal of individual weight was the most common means of estimating the anthelmintic dose used in sheep (78.6%) and goat (85.1%) flocks. The mean yearly drenching rate in lambs and ewes were 2.5 ± 1.7 and 1.9 ± 1.1, respectively, whereas it was 1.0 (once a year) in goats. However, these figures were higher in sheep in the coastal area with a rate of 3.4 and 2.2 in lambs and ewes, respectively. Benzimidazoles were the predominant anthelmintic class used in sheep flocks (64.9% in 2007), whereas benzimidazoles and macrocyclic lactones were both equally used in dairy goat flocks. In the period of 2005-2007, 46.3% of the sheep flocks never changed the anthelmintic class. The dose and move strategy was practiced in 33.2% of the sheep flocks.
The present study showed that inaccurate weight calculation gives a risk of under-dosing in over 90% of the sheep and goat flocks in Norway. Taken together with a high treatment frequency in lambs, a lack of anthelmintic class rotation and the common use of a dose-and-move strategy, a real danger for development of anthelmintic resistance (AR) seems to exist in Norwegian sheep and goat flocks. This risk seems particularly high in coastal areas where high treatment frequencies in lambs were recorded.
Nematode parasitic disease remains one of the greatest limiting factors in successful, sustainable ruminant livestock production worldwide. Currently, the control of nematode infections still relies mainly on the use of effective anthelmintics, which often represent the simpler, safer and cheaper option . However, anthelmintic-resistant (AR) nematodes are now recognised as an important threat to the productivity and welfare of sheep in many parts of the world, including Europe . The profitability and sustainability of the goat industry are also seriously threatened by rapid development of AR .
A total of 825 questionnaires (51.6%) were returned, representing 587 sheep flocks (51.3% of those selected) and 238 goat flocks (52.6%). These flocks represented 74472 winter fed sheep, 20466 dairy goats and 262 fiber goats. All sheep flocks were considered together, independent of flock size. Fiber goats were represented in 14 (5.9%) of the goat flocks and were grouped together with the dairy goats in the calculations. Seventy (8.5%) of the flocks had both sheep and goats, but each of these was treated as either a sheep or a goat flock in the survey.
In the present study, the response rate was above 50%. The response rate for sheep flocks were 42.7% in flocks with 20-100 ewes, and 58.7% in flocks with more than 100 ewes. Compared to the total number of sheep flocks in Norway, flocks with less than 100 winter fed ewes were underrepresented. Similar surveys have been based on a lower response rate, ranging from 15% to 24% [16,25,28].
The present study has shown that the anthelmintic drenching routines used in small ruminants in Norway may contribute to the development of AR. Over 90% of the sheep and goat flocks had insufficient weight estimation for calculating correct anthelmintic dose. This combined with few farmers controlling their drench gun represents a high risk for under-dosing anthelmintics in these flocks. A high risk was also suggested by a high treatment frequency, especially in lambs in the coastal area, a lack of anthelmintic class rotation and a common use of a dose-and-move practice. The early detection of AR may be quite difficult [50,54]. In order to avoid or slow down the emergence of AR, correct use of anthelmintics, on-farm information of gastrointestinal parasite burdens and knowledge regarding how to maintain parasites in refugia have to be implemented in the worm control management. This includes focus on dose rate, anthelmintic class alternation, treatment frequency, stocking rate and new treatment strategies, such as targeted (selective) treatment in combination with faecal egg counts. Giving the farmers the right information regarding worm control is a key stone in preventing anthelmintic resistance. Since the distribution of anthelmintic resistant nematodes in Norway is unknown a national surveillance program for AR detection should be established.
The authors declare that they have no competing interests.
AVMD, CC, BG, NL, SV, OØ and SS initiated and designed the study. AVMD performed the questionnaire and recorded the data. AVMD and OØ performed the statistical analysis. AVMD and SS drafted the manuscript. All authors read and approved the manuscript.