Effects of red osier dogwood extract on growth performance, protein digestibility, tibia breaking strength, immune response, and gut health of broiler chickens in a coccidiosis vaccine challenge model.

As the poultry industry moves away from using antibiotics as growth promoters due to concerns about antibiotic resistance, challenges such as coccidiosis, heat stress, and Salmonella, which were previously controlled, have become more common. Polyphenol-rich phytogenic feed additives improve intestinal development, exhibit antimicrobial and antioxidant effects, and boost growth performance. Red osier dogwood extract (RDE) is rich in polyphenols and enhances chicken growth, gut microbiota, and intestinal health and has mitigated the effects of Salmonella and heat stress in broilers. However, no study has demonstrated the effect of RDE on chickens challenged with coccidiosis. This study examined RDE's effects on growth, digestibility, meat and organ yields, bone strength, immune response, intestinal morphology, and gut microbiota in coccidiosis-challenged broilers. A total of 336 one-day-old mixed-sex Ross 308 broiler chicks were randomly assigned to 3 dietary treatments: Control corn-soybean meal diet (CON), CON + 0.15 % RDE, and CON + 0.30 % RDE. On d14, half of the birds were challenged with a 12x label dose of Immucox 3®, and the other half received the same volume of saline solution. Each dietary x challenge treatment had 8 replicate bioassay cages with 7 birds/cage. Jejunum tissue, ileal content, and blood samples were collected on d21. Meat and organ relative weight, left tibia, and ileal content were collected on d28. Coccidiosis challenge increased bursa weight, decreased crypt depth (P= 0.0048), villus height to crypt depth ratio (VH:CD) (P= 0.0004), liver weight (P= 0.0001), cecal (P= 0.0174) alpha-diversity, and the relative abundance of beneficial bacteria (P< 0.05). RDE increased (P = 0.0179) the weight of spleen linearly, without affecting bursa and liver weight, suggesting a beneficial immunostimulant effect, given that there was a quadratic increase in IgM titers (P = 0.0340) and crude protein digestibility (P = 0.0429), with 0.15 % RDE yielding the highest values, and 0.30 % RDE improved feed intake and body weight compared to CON. In the challenged group, 0.15 % yielded higher (P < 0.05) villus height and VH:CD than 0.30 %. Therefore, given the evidence that RDE benefits growth performance at 0.30 % inclusion, while 0.15 % inclusion optimizes gut microbiota and intestinal integrity in challenged chickens, RDE inclusion has potential benefits for promoting the health and growth performance of broiler chickens.