Lambs leap and play while ewes graze the lush green grass. It’s a beautiful spring image. However, managing the parasite load of ewes and lambs can be a challenge for organic farmers, particularly in the spring.
Read on to learn more about how to keep ewes and lambs healthy.
Managing internal parasites in sheep
The goal in organic sheep production is to manage, not eliminate, internal parasites. A healthy animal can tolerate low numbers of parasites. However, a heavy parasite load, particularly in a stressed animal, can lead to poor weight gain, a loss of condition, anemia and even death. The key is having healthy animals and minimal exposure to parasites.
To avoid a build-up of parasites on pastures and in animals, organic farmers focus on pasture rotation, nutrition and breed/individual selection. According to the 2020 Canadian Organic Standard (32.310 subclause 6.6.2): “ The operator shall not administer:…c) synthetic parasiticides, except by way of an exception provided in 6.6.11.” The exception is listed at the end of this article.
To manage internal parasites, Organic Science Cluster (OSC) researchers led by Dr. Andrew Peregrine are learning more about the life cycle of parasites on Canadian sheep farms. The following describes a simplified life cycle of the most common and problematic internal parasites on Canadian sheep farms
- Trichostrongylus spp.,
- Haemonchus contortus (barber-pole or wireworm), and
- Teladorsagia circumcincta (brown stomach worm).1
The life cycle of parasites is complex with various phases. It starts when parasite eggs are excreted by infected sheep. Within fecal pellets, the larvae grow and develop. At 15-20C, it takes about three weeks for eggs to hatch and develop into the infective stage. In moist, warm conditions, larvae can travel up to 30 cm away from where they were deposited and 5 cm up stalks of grass.
The optimal temperature for the black scour and brown stomach worms is 16-30°C, while the barber-pole worm prefers humid and warm conditions (25-37°C).
Under freezing or very dry conditions, larvae can become dormant. Many species can survive Canadian winters while dormant. However, research led by Drs. Peregrine and Menzies found that H. contortus does not overwinter well on pastures. According to University of Guelph researcher Laura Falzon, “Very few barber-pole worms (which are considered the most pathogenic since they feed on blood) survive well on pasture, and those that do survive are not very infective in the spring time; therefore, the pastures are to be considered essentially clean of barber-pole worm after the winter.”
In the gut
After being ingested, the worms moult and feed on the sheep’s protein and blood. At this point, the parasites may do one of two things:
- During the grazing season, the larvae develop into adults and lay eggs, which are excreted two to three weeks after the larvae were ingested.
- If larvae are ingested by ewes in late summer, they often remain inactive all winter. During this time, they will not cause symptoms or be detected in fecal tests (which count worm eggs). In ewes, these larvae mature just before lambing, when the ewe’s immune system is stressed; this is called peri-parturient egg rise. The ewe may shed large numbers of parasite eggs which contaminate the pastures for the young lambs grazing with them. This peak in parasites around lambing may also cause parasitic disease in ewes. Lambs raised alongside ewes while inside barns or when the ground is snow covered would not become infected.
Stress, including nutritional stress, weakens a sheep’s immunity. Ewes carrying multiple lambs tend to have more stressed immune systems and heavier worm loads than ewes with single lambs.
A good diet helps animals tolerate and resist parasite loads. Keeping ewes on a good plane of nutrition before and after lambing may reduce their parasitic load and minimize the effects of the worms. In particular, the diet should contain adequate levels of ‘bypass protein’ (e.g., roasted soybean).
Certain forages, such as birdsfoot trefoil, chicory and sainfoin, contain ‘condensed tannins’ which may reduce parasitic infections in sheep. Condensed tannins inhibit parasites and increase the sheep’s resistance by improving their digestion of protein.1,2,3,4 Livestock should not be fed such plants exclusively, but rather as part of a forage mix. Using pastures with trees, particularly willows and conifers, may also reduce parasitic infections.5
Reducing exposure to parasites
Rotational grazing can help prevent a build-up of parasites on a pasture. Researchers found that sheep under intense rotational grazing (i.e., five days per pasture) tend to have lower worm egg counts than those on longer rotations.6 Rotating pastures every two to three weeks (once the forage is grazed to 1.5 cm in height) will maintain forage quality and reduce parasite populations to a certain degree. However, larvae can remain in their infective stage for up to three months in the summer. Overstocking exacerbates parasite problems.
Heavily contaminated pastures should rest for a year, or be plowed and re-seeded with forage or field crops. Rotating the pastures with cattle helps to control parasites while maintaining forage quality. Goats, however, host the same parasites as sheep, so use the same rest period between sheep and goats as you would when returning sheep to the pasture.
Thick thatch protects worms from freeze-thaw cycles and sunlight (which dries them out, thereby affecting their survival and development). To reduce thatch, farmers can clip or groom pastures, or graze cattle or horses.
Protecting the most vulnerable sheep from exposure
If possible, farmers should avoid putting sheep, particularly lambs and pregnant or lactating ewes, on wet pastures. Heavy morning dews and showery weather allow larvae to travel to the top of the grass where they are most likely to be ingested by sheep.
Lambs are born without immunity to parasites. Lambs born on pasture are exposed to high levels of parasites from the start – because that is when the ewes are releasing a high number of eggs. The time of peak infection in lambs varies based on the weather (or time of year, temperature). In hot, wet weather, the peak may occur in early summer. If the summer is cool, the peak might not occur until the fall. After four to five months of exposure to worms, the lambs develop immunity that helps them resist parasitic infection.
The timing of lambing and weaning affects parasite loads. One option to reduce parasite exposure is to lamb in late winter and wean early (5-6 weeks of age) before the ewes go onto pasture. This way, the lambs will not be exposed to the heavy parasite load shed by the ewes.
The stress of weaning makes lambs more vulnerable to parasitic infection. One option is to send lambs to market before weaning. Weaned lambs should graze the cleanest pastures, such as the pastures used the previous summer to graze ewes, not lambs. (Yearlings and non-lactating ewes shed fewer parasite eggs than lambs.)
Which sheep to deworm
The OSC research team studying sheep parasites do not recommend that producers treat all their flocks at specific times. Instead, they recommend:
- Monitoring the animals using fecal egg counts, weight gains, evidence of bottle jaw, diarrhea and FAMACHA scores.*
- Treat only when there is the need to treat.
- Treat only the animals that need treatment.
When it comes to treating pregnant ewes, Dr. Menzies suggests treating ewes that are lambing for the first time, ewes that are carrying multiples, and ewes that are in poor body condition.
Lambs can be monitored during the summer by checking their condition and weight gain, and through fecal egg counts. To avoid disease and possibly death, lambs should be treated when they show signs of parasitism or when fecal egg counts are high.
* Farmers compare the colour of the inside lower eyelid to pictures in the FAMACHA guide to identify individuals infected by H. contortus. Producers should not use the on-line score cards. Accurate scoring requires training and colours on-line may not translate into the true colour.
Ideally, farmers should rotate families of drugs every year or two. This reduces the risk of resistance more than alternating drugs between treatments within a year.
To avoid contributing to parasite resistance, researchers recommend that after deworming, sheep go onto lightly contaminated (not parasite-free) pastures for three to five days.7 Here, the sheep will ingest some non-resistant parasites, but their parasite load will remain low. After 3-5 days, the animals can go onto clean pasture. The sheep will now be infected with both resistant and susceptible parasites. The new pasture will soon be populated by parasites, but numbers will be low and not dominated by resistant parasites.
Alternatives to chemical dewormers
There is anecdotal evidence to support the use of various herbs to treat or prevent parasitic infections in sheep and goats. In most cases, the efficacy of the herbs has not been evaluated scientifically. There is some evidence of anti-parasitic action produced by garlic, various types of wormwood (Artemisia spp.), eucalyptus, tansy, fumitory (Fumaria parviflora), pumpkin seeds and neem oil.8,9,10,11 For most of these, however, only one or two studies have been conducted, or multiple studies have been conducted but with varying results.
Another option is Duddingtonia flagrans -- a fungus that produces sticky networks which trap nematode larvae. The spores can be given to sheep in a drench or given to lambs in creep feed. Several studies indicate that the treatment appears to be effective, however the product is not yet available in Canada(12). Diatomaceous earth (DE) in feed has also been suggested as a dewormer, however there is no scientific evidence of its effectiveness.
Raising sheep organically can be challenging in the face of parasite loads. Fortunately, there are resources available to help you, including the following Canadian publications.
The Canadian Organic Growers (COG)’s Living With Worms In Organic Sheep Production by P. Stockdale, P and A Macey (2008) and the Handbook for the Control of Internal Parasites of Sheep by P. Menzies et al (2008) available here.
The Organic Science Cluster projects described in this article were funded by Agriculture and Agri-Food Canada and the Ontario Sheep Marketing Agency.
This article was originally published at dal.ca
Canadian Organic Standard 2020 – 32.310 Subclause 6.6.11.
“Organic livestock operations shall have a comprehensive plan to minimize parasite problems. The plan shall include preventative measures, such as genetic selection, pasture management, fecal monitoring and assessments of tissue at slaughter, and emergency measures in the event of a parasite outbreak. Hygienic cleaning and disinfection methods for barns, such as power washing, steam washing, floor burning and lime washing, shall be included in the plan as well as down time (i.e., when the barn is vacant). By way of an exception, if preventative measures fail due to, for example, climatic conditions or other uncontrollable factors, the operator may use parasiticides that are not listed in Table 5.3 of CAN/CGSB-32.311, provided that:
a) observation of the animal, fecal test results, or assessment of tissue as appropriate for the species indicate that livestock is infected with parasites;
b) the operator provides a written action plan, with a timeline, describing how they will amend their parasite control plan to avoid similar emergencies;
c) the operator has written instructions from a veterinarian indicating the product and method to be used, including provisions to avoid developing parasite resistance, such as rotation of parasiticides;
d) withdrawal times are twice the label requirement or 14 days, whichever is longer;
If these conditions are met, the following restrictions apply:
e) the exception cannot be granted for a group of animals or an entire production unit for more than two years in a row for the same problem;
f) a dam from any species may receive only one treatment of parasiticides during gestation;
g) meat animals from any species less than 12 months old shall receive at most one parasiticide treatment. Meat animals 12 months of age or older that receive more than two parasiticide treatments in their lifespan shall lose their organic status;
h) dairy animals that receive more than two treatments in a 12-month period, whether of parasiticides, antibiotics or one of each, shall lose their organic status and go through a 12-month transition period;
i) dairy cull animals that receive more than two treatments with parasiticides over their lifespan shall never be considered organic for meat;
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2. Douglas, GB, M Stienezen, GC Waghorn, AG Foote. 1999. Effect of condensed tannins in birdsfoot trefoil (Lotus corniculatus) and sulla (Hedysarum coronarium) on body weight, carcass fat depth, and wool growth of lambs in New Zealand. New Zeal. J. Agr. Res. 42(1): 55-64.
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7. Menzies, P et al. 2008. Handbook for the Control of Internal Parasites of Sheep. University of Guelph.
8. Allan, J, P Doherty. 2008. Identifying and testing alternative parasiticides for the use in the production of organic lamb. OFRF report. ofrf.org/funded/reports/allen_98-03.pdf
9. Burke, JM, A Wells, P Casey, JE Miller. 2009. Garlic and papaya lack control over gastrointestinal nematodes in goats and lambs. Vet. Parasitol. 159(2):171-174.
10. Rahmann, G, H Seip. 2007. Bioactive forage and phytotherapy to cure and control endo-parasite diseases in sheep and goat farming systems – a review of current scientific knowledge. In: Landbauforschung Völkenrode, pp. 285-295.
11. Lans, C, N Turner, T Khan, G Brauer, W Boepple. 2007. Ethnoveterinary medicines used for ruminants in British Columbia, Canada. J. Ethnobiol. Ethnomed. 3(11):1-22. oacc.info/ResearchDatabase/res_ethnoveterinary_ruminants.asp
12. Stockdale, P, A Macey. 2008. Living with worms in organic sheep production. Canadian Organic Growers.