Feed particle size and live-attenuated coccidiosis vaccination interact to improve productive performance rather than significant effects on gastrointestinal tract development and meat quality in broilers

1. The present experiment assessed the influence of feed particle size (FPS) and live-attenuated coccidiosis vaccination (COV) at one day of age on the performance, serum biochemistry, gastrointestinal tract (GIT) development and meat quality of broiler chickens.2. The experiment employed a 2 × 2 factorial design of treatments, with two types of FPS (fine and coarse) and two COV programs (with and without vaccine) with six replicate pens per treatment each containing 20 broilers.3. Cereals were passed through 4 mm and 8 mm sieves to create feed mixtures with finely ground (FGF) and coarsely ground (CGF) particle sizes, respectively. Broiler maize, wheat and soybean diets were provided <i>ad libitum</i> from d 1 to 13, 14 to 26 and 27 to 39 of age, respectively.4. At d 13, 26 and 39, birds fed on CGF had higher body weight and weight gain (<i>p</i> < 0.01) compared to those receiving FGF. During the starter period, vaccination increased FI in chicks fed FGF; however, this effect was not observed in birds fed CGF (FPS × COV interaction; <i>p</i> < 0.01). At all control points, significant FPS x COV interactions (<i>p</i> < 0.05) were noted for feed conversion ratio (FCR) with COV negatively impacting FCR only in the FGF-fed broilers.5. Serum biochemistry and GIT characteristics tended to be affected by COV. However, birds fed on CGF had relatively shorter and lighter small intestines compared to those consuming FGF (<i>p</i> < 0.01). The water holding capacity in breast meat decreased in relation to COV (<i>p</i> < 0.01).6. The results indicated that coarse grinding of feed was more effective in accommodating COV-induced growth retardation in broilers when compared to fine grinding.