This method applies treatment at the anticipated beginning of the disease or during the incubation period. To carry this out, there are a number of essential components:-

• The specific organism associated with the disease should be identified.
• The medicine sensitivity of the organism should be identified.
• The incubation period (the time from exposure to the organism to clinical symptoms) should be known.
• Last, and most important, the point at which the disease process starts and when it becomes clinically apparent should be determined. Medication can then commence prior to this point.

Strategic medication (Fig.4-10) is usually carried out in the feed but it can also be applied in the drinking water or by injection using long-acting preparations. It can also be applied to eliminate disease from a group of pigs. A good example would be to prevent possible swine dysentery in purchased pigs on entering a finishing herd. In this case the feed could be medicated with either lincomycin (110g/tonne) or tiamulin (100g/tonne) for the first 14 days during isolation on the farm. If strategic medication is carried out routinely, medicated feed must be held continuously in a designated bin.

A typical example would be the use of high levels of oxytetracycline, (500-800g to the tonne), in growing pigs to control severe outbreaks of enzootic pneumonia. The procedure would be to medicate all the pigs for seven days, one week after entry into the houses or approximately ten days prior to the commencement of clinical symptoms.

Thus each week a selected group of pigs would commence treatment to prevent the development of extensive lesions in the lungs and yet allow immunity to develop. An alternative strategy would be an injection of long-acting OTC given at a predetermined point. This method is of course more labour intensive. Strategic medication by injection is easier to apply in younger pigs. Fig.4-11 indicates some of the diseases where it can be used and the times of application.

The following on-farm case histories illustrate some of the uses for strategic medication:-

Enzootic pneumonia
Farm A was a 200 sow herd producing pigs for sale at 90kg. Its buildings were poorly insulated and due to the bad economic state of the industry at the time, no capital was available to improve the environment other than by managemental means. Severe bouts of coughing developed on this farm approximately three weeks after pigs moved from the first stage rearing accommodation into the finishing houses. Post mortem and lung examinations showed extensive lesions of enzootic pneumonia associated with secondary pasteurella infections, the latter shown to be sensitive to chlortetracycline (CTC). The first cases of clinical pneumonia became evident starting 10 days after the pigs moved into the finishing house. Commencing on day eight after entry, pigs were medicated with 600gm/tonne CTC for a period of seven days. This had a dramatic effect on reducing the incidence of disease and in particular, the numbers of pigs requiring individual treatment. The variability in growth was reduced. Initially, this was a herd with young breeding but as they matured, the time of onset of disease changed to appear five weeks after moving in to the finishing houses. The strategic medication was therefore given two weeks later.

Atrophic rhinitis (AR)
Herd B was a 1200 sow unit showing clinical atrophic rhinitis at a visual level of 15%. Toxigenic pasteurella and bordetella bacteria were isolated and were found to be sensitive to trimethoprim and amoxycillin. All piglets were injected with a long-acting preparation of the latter medicine at day seven, and again at weaning at 21 days. Pigs were further medicated with oxytetracycline in-feed for 14 days post-weaning. For a period of six months following this, the incidence of atrophic rhinitis at a visual level dropped to 2%. It then, however, started to rise again to a 7% level. Apparently the stockperson had decided to inject the pigs at 10-14 days of age because this was more convenient. This allowed early establishment of pasteurella organisms in the nose and a considerable amount of damage. When the injections were moved back to the seven day point the problem again returned to low levels. This example illustrates the importance of determining by trial and error, the critical point at which strategic medicine therapy should be given. At the time of this disease problem vaccines to prevent atrophic rhinitis were not available

Actinobacillus (Haemophilus) pleuropneumonia (App)
This disease can be a very difficult one to control especially in its severe form. Herd C was a 250 sow herd producing pigs for slaughter at around 70kg liveweight. At nine weeks of age pigs were moved from the nurseries (flat decks) into a second stage rearing accommodation and within seven days of entry, severe outbreaks of pleuropneumoniae occurred. In view of the very short incubation period of this disease (12-48 hours) strategic medication can be difficult to apply. In this particular case, medication was applied immediately the first clinical case became apparent. To obtain a very rapid response, chlortetracycline was placed in the header tanks in the drinking water for a period of 72 hours. The response on this farm was quite dramatic, but perhaps even more importantly, the trigger factors associated with a drop in energy intake and variable temperatures in the house were then corrected. This reduced the strategic medication requirements which illustrates the importance of management.

Streptococcal meningitis (SM)
Farm D was a 350 sow herd previously free of streptococcal meningitis. It became infected with a virulent strain of Streptococcus suis type 2 through the purchase of a group of gilts which were carrying the infection. The introduction of disease caused severe problems in the nurseries (flat decks) where it regularly appeared approximately 16 days after entry into the house. All pigs were medicated through the drinking water with potassium penicillin V commencing on day 10 through to day 17. High numbers of pigs become carriers of the organism in their tonsils within 2 weeks of occupying nurseries and a variable number of such animals then develop the disease. The object of applying water medication at this stage was to reduce the level of infection. The disease reached its peak with some 15% of each batch of pigs moved into the house requiring individual treatment. Strategic medication reduced this down to less than 1%.

Swine dysentery (SD)
Farm E was a finishing farm purchasing approximately 10,000 pigs per annum. It had previously been infected with swine dysentery and an eradication programme was successfully carried out. It was however, periodically committed to buying pigs from unknown sources, in response to market forces. In order therefore, to protect the herd all incoming pigs were strategically medicated in groups of 200 when they entered the farm whilst in isolation premises. These premises were completely emptied and disinfected between batches. On arrival the pigs were medicated in the water with ronidazol for a period of five days, together with in-feed medication at 60gm/tonne for a further seven days. These procedures prevented the appearance of disease.

These on farm situations illustrate some of the methods by which strategic medication can be used to good effect to control disease and at the same time be cost effective. There are a variety of medicines available and Fig.4-10 lists some of these, together with in-feed dose rates. However, if you are thinking of adopting strategic medication discuss it with your veterinarian first so that he can advise you on the best type of medicine, the dose level and its timing. Fig.4-11 shows possible time applications for strategic medication.