When speaking to farmers during new client or ‘Vet Declaration’ visits, one of the questions I always ask is; ‘where do your replacements come from?’

The answer to this question varies. Some people are breeding their own, others buy in (from one source or multiple), some won’t breed at all and bring all stock in as stores. Even flocks that are closed from a ewe point of view will often have to bring male genetics onto the farm in the form of a new tup. By asking this question your vets are really asking about your disease control; the key elements of which are described in this article!
There are four key areas of concern when bringing new animals onto farm. These are: sheep scab, contagious lameness, fluke and roundworms.

Sheep Scab

Scab is caused by a mite (Psoroptes Ovis) which is highly contagious and viable off the host for around 17 days. Close contact with other infected animals is key for transmission – be it at a market or when housed in winter or at lambing time. Scab infestation will spread quickly throughout the flock leading to loss of fleece, intense itching, and weight loss in severe cases.
When bringing new animals on farm there are two options to mitigate the risk of introducing scab. The most sustainable option is to bleed the new stock and look for antibodies to the parasite. This needs to be done two weeks after they arrive on farm – it takes two weeks for the immune system to generate antibodies. If the animals test negative, we can be confident that they are scab free at the point of entry.
The second option is to treat all new additions either in response to a positive result to the blood test or if they pose a high risk (come from a hotspot area, common grazing, or do not know treatment history).
There are several different treatment options to consider; most commonly a macrocyclic lactone (clear) wormer or dipping using organophosphates. Dipping is preferable due to increasing resistance to ML wormers. It is always best to assume a high risk and treat animals if the history is unclear. Please speak to the vet team if you have any questions about product choice.

Image: Psoroptes Ovis mite found on a sheep affected with scab.

Contagious Lameness

Contagious lameness refers to both footrot (Dichelobacter nodosus) and contagious ovine digital dermatitis (CODD – Treponema spp.). These bacterial causes of lameness are highly infectious and cause both significant production loss and welfare concerns.
Footrot presents classically as inflammation between the toes with under running of horn and a characteristic foul smell. CODD presents as sudden onset severe lameness where the hoof capsule is sloughed, and angry red lesions appear at the coronary band.
In addition to examining animals for obvious lameness, foot lesions or misshapen feet at the point of sale, there are other key steps that we can take to try and minimise the risk of introducing contagious lameness when bringing in new stock.
The most important is to footbath animals in 3% formalin as they come off the trailer. The footbath needs to be deep enough and long enough to completely submerge all feet (approx. 6cm deep), and should ideally be corrugated to spread claws. It is good practice to bath the animals at least twice, and to spray off feet before animals enter the footbath – this removes organic debris which reduce the effectiveness of formalin. Animals should then be stood in a yard for a minimum of one hour post bathing (yarding animals on purchase is also beneficial from a roundworm control point of view – see below).
It is important to note that footbathing in formalin will not work as a treatment for contagious lameness. Animals already showing signs of lameness should be isolated and treated with topical oxytetracycline and NSAID (+/- systemic tetracyclines or macrolides depending on the severity of lameness). Please speak to your vet if you have any concerns about lameness control.

Fluke

Liver fluke (Fasciola hepatica) is a flat worm which persists in different parts of the liver depending on its stage of development. Immature juvenile fluke destroy liver tissue – if the burden is heavy this can cause acute disease, which ultimately may culminate in death. Adult fluke reside in the bile ducts and shed eggs which are passed in faeces. Adult fluke are usually responsible for chronic disease – ill thrift and bottle jaw.
Liver fluke have an indirect lifecycle, meaning they need a mud snail to act as an intermediate host. Mud snails require wet conditions to survive, which is why wet ground is a key risk factor for infection.
The key risk with purchasing new stock is not just introducing fluke eggs to your pasture, but introducing fluke that are resistant to triclabendazole (one of our key treatments). Different flukicides act on different ages of parasite, however triclabendazole is the only product that will kill all ages. It is therefore of great importance in the treatment of acute infestation.
The way to combat the introduction of triclabendazole resistant fluke is to use two products as part of your quarantine protocol. Treat all animals with triclabendazole (if they have a high fluke risk) as they arrive on farm. This should kill all stages of fluke. Treat animals again in six to eight weeks with a closantel based product. This will kill any remaining fluke that are triclabendazole resistant (closantel only kills fluke over six weeks old). If possible, animals should be turned out onto dry pasture between these two treatments (or kept in). It is important to note that sheep can pass fluke eggs for three weeks after mature fluke have been killed. It is good practice to keep sheep in the quarantine area for four weeks after the last treatment.

Image: Adult Fasciola hepatica from a liver infested with fluke.

Roundworms

The key roundworms of sheep are Teladorsagia and Trichostrongylus spp. These worms have a direct lifecycle and are key contributors to ill thrift, scour, and poor immune function (especially in lambs).
Adult sheep have relatively good immunity to roundworms – only very extensive burdens are likely to cause clinical signs. By treating adult sheep we are aiming to reduce the contamination of pasture for lambs in their first grazing season. The exception to this rule is Haemonchus contortus, to which adult sheep struggle to produce an immune response. As such, heavy burdens of this worm can cause severe clinical signs – seen as pale mucus membranes due to blood loss.
In a similar way to fluke control, a good way of minimising the risk of bringing resistant worms onto farm is to treat new animals with a combination of products. Gold standard would be to use a combination of group 4 (orange) and group 5 (purple) drenches on arrival to ‘clear animals out’ as there is little resistance to these products. Silver standard would be to use either a group 4 or 5 drench in isolation, or to use them in combination with a clear wormer. Using multiple wormers is a belt and braces method of ensuring any resistant roundworms are killed by a different product. Never mix products in the dosing gun and always ensure you treat to the heaviest sheep in the batch!
Yarding sheep for 24-48 hours after arrival and treatment with anthelmintic is good practice. This allows time for the treatment to work and will minimise contamination of pasture with eggs. A faecal worm egg count should be done post treatment to assess efficacy of the wormer. Always place new stock onto ‘dirty’ pasture after worming (had your sheep on in last 12 months). This will allow them to pick up worms specific to your farm and prevent any resistant worms (not killed by the quarantine treatment) from dominating that pasture.

Infectious abortion

Enzootic abortion (Chlamydophila), Border Disease (pestivirus) and Toxoplasma gondii (protozoa) are always of concern when buying in breeding or in-lamb ewes.
Abortion products are key to the transmission of Chlamydophila, and therefore it is good practice to lamb new sheep separately to the current flock for their first season. These animals will abort very late (last three weeks gestation) and will have acquired the infection in the previous lambing season. Contact with your sheep at lambing time could put them at risk for the next year.
Border Disease is thought to be associated with persistently infected animals (PI – shed high volumes of virus). This can include tups which can spread the virus venereally. Again, avoid lambing new ewes and the existing flock together for the first season. A blood test is available for Border Disease.
Toxoplasma gondii is not shed between sheep but is acquired when animals ingest cat faeces on pasture. It usually presents as a high barren rate at scanning. It is always good practice to buy from a farm that vaccinates breeding animals for both enzootic abortion and toxoplasma.
If you have any concerns or questions, please speak to one of the vet team.