To some people the title of this first chapter might suggest that it is just concerned with fencing, keeping your sheep in and other people’s out. Of course this is an important part of managing flocks that are kept on enclosed land, but flock security has a much wider meaning, encompassing all the precautions that should be taken to minimize the introduction of costly infectious diseases.

Types of Flock

Flocks can be simplistically classified according to how they are managed, together with the associated disease risks.

Closed purebred flocks: Closed flocks breed their own replacements and have no contact with sheep in other flocks. In most of these flocks there will be the occasional purchase of new rams, and these are the risky animals as far as possible disease introduction is concerned.

Lowland flocks of crossbred ewes: These include Mules, Welsh or Scotch halfbreds, and Greyfaces or other recognized crosses. Unless a hill flock to breed these is in the same ownership, young replacement ewes are likely to be purchased every year, meaning annual opportunities for disease introduction. Terminal sire breed rams (such as Texel, Suffolk and Charollais) are also likely to be purchased annually.

Purebred isolated hill flocks: These graze extensively, but are prevented from mixing with other flocks by fencing or natural geographic features. These flocks may also make occasional purchases of rams, which pose a potential risk.

Hill flocks that graze extensively on land with access by several flocks: These are at risk of picking up disease from each other, and unless there is cooperation from all flock owners involved, it can be extremely difficult to control infectious disease, particularly sheep scab.

Store lamb finishing flocks: In such flocks weaned lambs may be purchased from many sources and mixed together, creating the perfect opportunity for disease spread.

Fig. 2 Closed purebred flocks should be able to achieve high health status, but beware of the risks in bringing in new rams.

Fig. 3 Double fencing makes sure that a closed flock cannot contact neighbouring animals, and keeps stray sheep out.

Of course there are many more types of flock than those described above, but the examples serve to show that the more mixing of sheep that occurs, the greater the risk of introducing diseases that can have a serious impact on the welfare and profitability of the flock. There are other opportunities for disease spread, for example:

Two real examples will serve to highlight the possible consequences. In one flock of 500 ewes, two new rams were purchased at the beginning of the breeding season. These were mixed with the resident rams and used to mate the whole flock. After housing for lambing, a number of the sheep were seen to be itching, but the vet was not consulted until part way through lambing, by which time many of the sheep were affected. A diagnosis of sheep scab was made, and this presented a huge problem of how to control it because of all the very young lambs that were now present and continuing to be born. Much money had to be spent on injectable treatments but the situation was not fully brought under control until several months later, after shearing, when all animals could be treated at the same time. Circumstantial evidence was that the disease had been introduced with the two purchased rams.

In another small hobby flock, a spare lamb was acquired to foster on to a ewe that had lost her own lamb. It was noticed that other lambs in the flock of origin had crusty eye discharges. A few weeks later several of the ewes developed runny eyes, progressing to severe eye infection and blindness. Gradually most of the ewes became infected and required repeated treatment before the problem eventually subsided several months later.

Both of these cases show how the introduction of one or two sheep into a new flock can lead to much cost in terms of time and drugs, which could have been avoided with a higher awareness of the risks involved.

There is a huge list of diseases that can be introduced in this way, most of which are covered at relevant places in this book. The following are the most important and common:

For a small number of these diseases, health or monitoring schemes are available so that sheep can be purchased as being certified free of a particular disease or diseases, and it is well worth investing in such sheep if available; but in the overall scheme of things, these sheep form only a small percentage of those traded each year. The diseases covered by these schemes are:

How to Reduce the Risk of Buying in Disease

Always examine animals carefully before purchase. Do not buy groups that contain lame animals, itching animals or coughing animals, or any other obvious problem, however cheap they seem – they will turn out to be expensive in the long run!

Keep a purebred flock which can breed its own replacements. One example of a breed that has flourished in recent years is the Lleyn, originally a numerically quite small breed from North Wales that is now extremely popular as a replacement for the Mule. It has similar characteristics to the Mule, particularly milkiness and prolificacy, and crosses well with a terminal sire such as the Texel, but a proportion of the flock can be bred pure to provide homebred ewe lambs. However, this breed is not suitable for hill areas where hardy breeds such as the Swaledale, Cheviot, Blackface and Welsh Mountain thrive. There will always be a supply of young crossbred breeding ewes from these areas: in fact they form an important part of the income for these farms, and producing them with a high health status will increase their value and reassure purchasers.

Check the disease history of the supplying flock when buying rams for purebred flocks such as above, examine the animals carefully, and quarantine them after purchase (see below).

Buy rams as far as possible in advance of the next breeding season – if necessary buy direct from breeders. One of the main problems in buying rams is that many of the sales do not take place until very near tupping time, which doesn’t allow much opportunity for quarantining them.

Buy straight off the farm, rather than through a market, if replacements are purchased each year, from as small a number of suppliers as possible.

Try to purchase from the same sellers each year if purchasing through a market, if you are happy with their stock.

Never buy sheep of unknown origin, particularly older sheep that have bred before. These have a high risk of bringing some of the common forms of abortion and other diseases into the flock.

Be careful of bringing in spare lambs from another flock for fostering.

Quarantining Purchased Animals

It is good practice to keep newly purchased sheep, both ewes and rams, separate from those already on the farm. The longer they can be kept apart, the better, but at least a month is recommended. This should allow time to check for infectious foot diseases such as footrot and CODD, and to treat for sheep scab, anthelmintic-resistant worms and fluke, if applicable. The best drug combination to cover scab and anthelmintic-resistant worms may be injectable moxidectin (group 3 AV), which will control scab, and a drench of the new group 4 AD wormer, monepantel. Alternatively, dipping in an organophosphorus (OP) dip will deal with scab, lice and chorioptic mange, and drenching sequentially with moxidectin (group 3 AV) and monepantel (group 4 AD) will guard against introducing anthelmintic-resistant worms. For forty-eight hours after dosing, sheep should be kept on yards or in a field not to be used for grazing sheep (for instance, arable) so that all viable worm eggs will have been passed. However, it is always best to take the latest advice on this complicated subject from your vet as part of a flock health programme. See also Chapter 7.

For breeding ewes, one of the biggest risks is buying in one of the common abortion agents, particularly that causing enzootic abortion (Chlamydophila abortus). If it is possible to manage these ewes as a separate group, preferably lambing after the main group, this minimizes the risk of spreading this disease, should it occur, to others. Vaccination will reduce, although not eliminate, the risk of introducing this infection (see Chapter 4).

Some of the diseases mentioned above have long incubation periods, so it may be several years before it is realized that they are causing problems, by which time much of the flock may be infected. For example, with maedi, it is estimated that 40 per cent of the flock is likely to be infected by the time clinical cases are seen.

Fig. 14 Spare lambs brought in from another flock may seem to be a good idea, but they are risky as a potential source of disease. This lamb has dirty eyes and a dirty nose.

Fig. 15 A good area of concrete or similar hard standing allows sheep to be held after purchase so they can be dosed with wormers to prevent anthelmintic-resistant worms being brought in. Food and water should be provided if the sheep are to be held for more than an hour or two.

Fig. 16 Enzootic abortion is spread from infected to uninfected ewes at lambing time. If possible, lamb replacement ewes separately in their first year in case they bring infection with them.

Safeguarding the Health of Newly Purchased Animals

Remember that new sheep introduced to a farm may not be vaccinated against common diseases such as clostridia, and may be exposed to other diseases to which they have no immunity; examples of these are toxoplasmosis, tick-borne fever and louping ill.

The most urgent task is to carry out any necessary vaccinations, particularly those for clostridial diseases (see Chapter 4 for vaccination schedules). If some of the land is infested with ticks, be careful not to introduce sheep from non-tick areas at crucial times in the reproductive cycle, such as tupping time and pregnancy, as inevitable infection with tick-borne fever causes temporary infertility in rams and abortion in ewes.

Safeguarding the Whole Flock

Keep infection out by enforcing disinfection of visitors to the flock, cleansing your equipment, boots and vehicle tyres after visiting other flocks, markets, abattoirs and so on, and by maintaining good perimeter fences if this is possible.