Development of a coccidiosis disease challenge model using a commercially available live oocyst vaccine.

With growing cross-disciplinary collaboration among researchers it is increasingly important to record detailed methodology to prevent the repetition of preliminary experiments. The purpose of this paper was to explain the development of a coccidiosis challenge model for the investigation of dietary interventions to coccidiosis in broiler chickens. The objectives were to select a dose of mixed species coccidial vaccine and evaluate the suitability (ability to produce a consistent, marked change) of selected response variables important to nutritional studies at different times post-infection (PI). Coccivac-B or Coccivac B-52 (Merck Animal Health) were evaluated as the source of coccidia in three trials. Trials one and two were randomized complete block designs with four doses (0, 10, 20, or 30 times (x) label dose) of Coccivac-B administered to 12 replicate cages of 6 birds by repeater pipette (trial one) or gavaging needle (trial two). Trial three used a completely randomized design with 0x or 30x label dose of Coccivac-B52 administered by gavaging needle to six replicate cages of 6 birds. Birds were ravaged at 15 d of age and response criteria were evaluated 7 d PI in all trials and again at 10 d PI in trials one and two. All means are reported in order of increasing coccidia dose with significance accepted at  P  ≤ 0.05. Broiler performance was not affected by coccidia in trials one or three but grew poorer with increasing dose from 0-7 d PI in trial two (body weight gain: 465, 421, 388, 365 g; feed to gain: 1.37, 1.47, 1.52, 1.58). As coccidia dose increased,AME n decreased (trial one: 3387, 3318, 3267, 3170 kcal kg -1 ; Trial 2: 3358, 2535, 2422, 2309 kcal kg -1 ; Trial 3: not measured), while relative weight, length and content for intestinal sections increased (trials one through three). Gross lesion (duodenum, jejunum/ileum, caeca) and oocyst count scores (jejunum/ileum, caeca) increased with dose, however gross scoring often suggested infection in unchallenged birds, a finding unsupported by oocyst count scores. At 7 d PI there was no correlation between midgut gross lesion score and midgut oocyst count score (r = 0.06,  P  = 0.705), but caecal scores were weakly correlated (r = 0.55,  P  < 0.001). Administering coccidia via repeater pipette (trial one) resulted in respiratory distress in some birds while use of the gavaging needle (trials two and three) successfully induced intestinal damage in chickens without resulting in coccidia related mortality. Thirty times the label dose at 7 d PI resulted in the greatest number of response variables that produced a consistent, marked change. Therefore, consideration should be given to these conditions when designing future coccidiosis challenge models using vaccines as a source of coccidia.