History

The farm had been re-furbished for broiler parent chickens about 1 year prior to the current case. Prior to this refurbishment the farm had been used for rearing 3 broiler parent chicken flocks, and prior to this turkeys had been reared. None of these chicken flocks are believed to have suffered any disease problems. Some nest boxes had been introduced from another site which had a history of Pasteurellosis. These nests had not been used for 9 months prior to the transfer and were said to have been creosoted and then thoroughly disinfected before and after transfer.\par The flock was hatched by Ross Breeders (Ross 1 (308) type) on April 21st 1993 and reared at a dedicated rearing site according to the normal practices of the company. As far as is known there were no unusual problems during rear and the birds were oil-vaccinated and transferred on August 18th, aged 16 weeks, having undergone chlortetracycline treatment on the rearing farm (August 6th to 15th). They had not been vaccinated against Pasteurellosis because neither the rearing farm nor the egg-production farm had a previous history of Pasteurellosis in chickens. They were treated with a competitive-exclusion product (Aviguard) on the day after arrival at the laying site. Three thousand five hundred birds were placed in each of the three houses, with 400 low-weight birds being placed in house 3. Post-mortem examinations were carried out by a local veterinary surgeon at 20 weeks (8 birds), 22 weeks (3 birds) and 24 weeks (4 birds). At 20 weeks the veterinarian mistakenly believed that the birds had recently come off antibiotic medication. At 22 weeks amoxycillin was prescribed. The findings at all three examinations included infectious arthritis and swollen heads/facial cellulitis. Respiratory viral challenge (Infectious Bronchitis and/or Avian Rhinotracheitis), secondary infections and staphylococcal joint infection were suspected. Apparently the dose of amoxycillin actually used was only 10 mg/kg over a period of 10 days (21-30th September, birds aged 22 weeks). The normal therapeutic dose would be 20 mg/kg. Table 1, on the next page, shows the list of significant events with respect to the case.

Table 1. Broiler Parent Flock - Log of medication and other interventions.

Date Week Occurrence

--------- ------ ---------------------------------------------------------------

1/8/93 15 Chlortetracycline 300 ppm in feed for 10 days

8/8/93 16 Transfer to production farm - vaccinated Oil-based IB/ND/IBD, Competitive Exclusion 2 days

15/8/93 17

22/8/93 18

29/8/93 19 A few birds were noted to have swollen heads

5/9/93 20

12/9/93 21

19/9/93 22 Amoxycillin 10 mg/kg/day for 10 days in water. Blood samples taken

26/9/93 23

3/10/93 24 Blood samples taken.

10/10/93 25 Field veterinary visit. Chlortetracycline 300 ppm in feed started.

17/10/93 26 Affected females and all males injected with long-acting oxytetracycline (TM-LA).

24/10/93 27

31/10/93 28 Sodium Salicylate 1 g/litre in houses 1 and 2

7/11/93 29 230 Pasteurella-vaccinated males from another farm added though penned separately.

14/11/93 30 In-feed medication changed to potentiated sulphonamide for 10 days

21/11/93 31 Vaccinated males given 2 i.m. injections of long-acting tetracycline 3 days apart then released.