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Over a period of six months, approximately 4700 blood samples were collected from 97 pig-finishing farms in the provinces of Noord-Brabant and Gelderland and screened for antibodies with respect to Aujeszky's disease virus (ADV), porcine influenza virus (PI) and Actinobacillus (Haemophilus) pleuropneumoniae (App). There were significant differences in the percentages of seropositive pigs between the two provinces, which may be related to the difference in the density of the pig population in the two provinces. In practice, it was possible to perform a reliable sera collecting procedure at the slaughterhouse. No farms remained seronegative with respect to most of the disease agents during the sampling period. There was a high degree of variation in the percentages of seropositive pigs per farm as to most of the disease agents. Evidence was found that animals that were seropositive with respect to ADV were significantly more susceptible to becoming seropositive with respect to App. serotype 2, and vice versa. The same connection was observed for PI serotype H1N1 and PI serotype H3N2. Furthermore, evidence was found that pigs seropositive with respect to PI serotype H1Ni only, or to PI serotype H1N1 and ADV or PI serotype H3N2 show a significant decrease in average daily weight gain compared to pigs that were seronegative.

Log book recording was done for twelve months on approximately 100 pig finishing farms in an Integrated Quality Control (IQC) project. This recording was designed to gain a better understanding of the extent and nature of the medication and vaccination on these farms. Vaccination against Aujeszky's disease was done on the majority of farms. This vaccination mainly consisted in a single, frequently intramuscular, injection. Vaccinations against swine influenza and infections due to Actinobacillus (Haemophilus) pleuropneumoniae were merely sporadic. The animals were dewormed in 58 per cent of the finishing periods, whereas they were given preventive treatment for sarcoptic mange in 23 per cent of the finishing periods. Not a single pig was treated with antibiotics and/or chemotherapeutic agents in 12.5 per cent of the finishing periods. The majority of finishing periods in which treatment was not carried out, were those having closed pig herds. To the extent that the farms were supplied with piglets by more breeders, there were fewer finishing periods during which treatment was omitted. The great majority of cases in which individual therapy was given, were treated for respiratory disorders. On 27 per cent of the farms, more than 10 per cent of the animals per finishing period were treated for respiratory disorders. Group medication was much less frequent: intestinal disorders did not have to be treated on 31 per cent of the farms, and 16 per cent did not require treatment for respiratory disorders. In the great majority of cases in which group treatment was required, this was given during the first sixty days of the finishing period. In view of the fact that there are marked differences in the degree to which pigs have to be medicated on the farms, recording the use of veterinary drugs on farms, could fulfil the function of a signal. On the basis of these signals, measures may be suggested in herd management programmes to ensure an effective and minimum use of veterinary drugs. Using a log book will also enable the pig farmer to estimate whether groups of animals may be sent to the slaughter-house without involving risks to public health.