Investigations into Increased Incidence of Severe Gizzard Erosions and Ulcerations in U.S. Commercial Broilers.

During a series of pathology surveys in four production complexes of a U.S. broiler integrator, the technical services veterinarians of an animal health company noted a high incidence of severe gizzard erosions and ulcerations (GEU), prompting further clinical investigation and a battery trial. No growth-promoting antibiotics or ionophore coccidiostats were used during the period of these surveys. All used tribasic copper chloride (TBCC) at ≤120 ppm added copper in broiler rations. Clostridium perfringens was isolated from 83% and 67% of gizzard lesions cultured in two complexes, and cecal C. perfringens most probable number determinations were higher in severely affected than in mildly affected or unaffected birds. Histopathology revealed both acellular koilin fusion defects characteristic of copper toxicity, as well as inflammatory cell infiltrates. Intralesional bacilli suggestive of C. perfringens were noted in 78% of affected flocks examined. Species E Aviadenovirus was isolated from one bird in one complex, and that bird had a single intranuclear inclusion body; no other flocks had Adenoviruses isolated or detected on PCR, nor any inclusion bodies. Other viruses detected were thought to be incidental. A pilot study using feed with supplemental copper from TBCC or copper sulfate and challenge with one of the isolated C. perfringens strains reproduced the lesions. A battery study was conducted with an unchallenged negative control group fed a diet with 16 ppm added copper, a group fed the control diet and orally challenged with 108 organisms of a field strain of C. perfringens at 21 and 22 days, and a group treated with the same diet containing 250 ppm added copper from TBCC and orally challenged with C. perfringens. Birds were necropsied at 23 and 28 days. All challenged groups developed lesions, with those receiving both TBCC and C. perfringens having significantly higher gross and histopathological lesion scores than the unchallenged negative controls. Lesions were qualitatively similar to those in the field and contained suspected C. perfringens bacilli. Because the levels of TBCC used in the commercial birds and in the battery trial generally have been considered safe, and because C. perfringens is usually regarded as a pathogen of the lower GI tract, the possible association of these two agents with GEU is a novel observation and warrants further investigation.

Investigaciones sobre el aumento de la incidencia de erosiones y ulceraciones severas en la molleja en pollos de engorde comerciales en los Estados Unidos. Durante una serie de estudios de patología en cuatro complejos de producción de un integrador de pollos de engorde de los Estados Unidos, veterinarios de servicio técnico de una empresa de salud animal observaron una alta incidencia de erosiones y ulceraciones severas de la molleja (GEU), lo que motivó una mayor investigación clínica y un estudio en batería. Durante el período de estas encuestas no se utilizaron antibióticos promotores del crecimiento ni coccidiostáticos ionóforos. Todos utilizaron cloruro de cobre tribásico (TBCC) con un nivel de ≤120 ppm de cobre agregado en raciones para pollos de engorde. Se aisló Clostridium perfringens del 83% y el 67% de las lesiones de molleja cultivadas en dos complejos, y las determinaciones del número más probable de C. perfringens en los sacos ciegos fueron mayores en aves severamente afectadas que en aves levemente afectadas o no afectadas. La histopatología reveló defectos de fusión de la capa córnea acelular característicos de la toxicidad por cobre, así como infiltrados de células inflamatorias. Se observaron bacilos intralesionales sugestivos de C. perfringens en el 78% de las parvadas afectadas examinadas. La especie Aviadenovirus E se aisló de un ave en un complejo, y esa ave tenía un único cuerpo de inclusión intranuclear; en ninguna otra parvada se aislaron o detectaron adenovirus mediante PCR, ni se observaron cuerpos de inclusión. Se pensó que otros virus detectados fueron incidentales. Un estudio piloto que utilizó alimento con cobre suplementario de cloruro de cobre tribásico o sulfato de cobre y con desafío con una de las cepas aisladas de C. perfringens reprodujo las lesiones. Se realizó un estudio de batería con un grupo de control negativo no desafiado alimentado con una dieta con 16 ppm de cobre agregado, un grupo alimentado con la dieta de control y desafiado por vía oral con 108 organismos de una cepa de campo de C. perfringens a los 21 y 22 días, y un grupo tratado con la misma dieta que contenía 250 ppm de cobre agregado de cloruro de cobre tribásico y desafiados por vía oral con C. perfringens. A las aves se les realizó la necropsia a los 23 y 28 días. Todos los grupos desafiados desarrollaron lesiones, y aquellos que recibieron cloruro de cobre tribásico y C. perfringens tuvieron puntuaciones de lesiones macroscópicas e histopatológicas significativamente más altas que los controles negativos no desafiados. Las lesiones eran cualitativamente similares a las del campo y contenían bacilos sospechosos de C. perfringens. Debido a que los niveles de cloruro de cobre tribásico utilizados en las aves comerciales y en el ensayo en batería generalmente se han considerado seguros, y debido a que C. perfringens generalmente se considera un patógeno del tracto gastrointestinal inferior, la posible asociación de estos dos agentes con erosiones y ulceraciones severas de la molleja es una observación reciente y justifica una mayor investigación.

Intra-cluster correlations for ceca Salmonella prevalence and enumeration from 40 experimental floor pen trials in broiler chickens using a seeder bird challenge model.

Floor pen trials are an efficient way to evaluate the effectiveness of potential Salmonella control interventions in broiler chickens. When treatments are allocated at the pen level, and outcomes are measured at the individual bird level, floor pen studies are considered to be cluster randomized trials. Estimating the sample size required to achieve a desired level of statistical power for a cluster randomized trial requires an estimate of the intra-cluster correlation (ICC) as an input. In this study, ICCs were estimated for the untreated challenged control group from 40 broiler chicken Salmonella pen trials performed using a seeder bird challenge model. The ICCs for ceca Salmonella prevalences ranged from 0.00 to 0.64, with a median of 0.17. The ICCs for ceca Salmonella log10(MPN/g + 1) ranged from 0.00 to 0.52, with a median of 0.14. These findings indicate that the effect of pen-level clustering is substantial in Salmonella floor pen trials, and it must be considered during both the study design and analysis. In a multivariable regression analysis, ICCs for ceca Salmonella prevalences were associated with the challenge status of sampled birds, age of birds at the time of challenge, and Salmonella serovar. ICCs were lower for studies in which a combination of direct (seeder) and indirect (horizontal) challenged birds were sampled, and for studies in which birds were challenged on the day of hatch or at one day of age. ICCs were higher for studies in which Salmonella Heidelberg was used as the challenge strain. These findings may be useful for investigators that are planning pen trials to evaluate Salmonella control interventions in broiler chickens. Choosing study design elements associated with a lower ICC may improve efficiency by leading to a larger effective sample size for the same number of experimental units.