Growth performance, breast yield, gastrointestinal ecology and plasma biochemical profile in broiler chickens fed multiple doses of a blend of red, brown and green seaweeds.

1. A total of 864 d old (male) Ross × Ross 708 broiler chicks were allocated to 48 floor pens (12 pens/treatment and 18 birds/pen) to investigate dose-response of a blend of seaweeds (SB) on growth performance, breast yield, jejunal histomorphology, microbial metabolites and community and plasma biochemical profile. 2. A maize-soybean meal diet was formulated with 0, 5, 10 or 20 g/kg of SB. Diets were formulated for a three-phase feeding programme (starter: d 0-10, grower: d 11-24, and finisher: d 25-42) and met or exceeded Aviagen nutrient specifications. Diets were allocated to pens (n = 12) balanced for body weight (BW). Birds had free access to feed and water, BW and feed intake (FI) were monitored by phase. One bird per pen was randomly selected on d 42, bled for plasma, and samples for intestinal tissue and caecal digesta were taken. Microbial DNA was extracted and submitted for microbial community profile using the Illumina Miseq® platform. 3. In the starter phase, SB linearly ( ≤ 0.01) improved BW, body weight gain (BWG), and FCR. However, the improvement was quadratic, such that there was no further improvement beyond 5 g/kg SB inclusion. Growth performance response to SB in the grower phase was similar to the starter phase, with the exception of FCR ( > 0.05). Overall, from d 0-42, a linear and quadratic ( < 0.01) response was observed for final BW (d 42), whereby birds fed 5, 10 and 20 g/kg SB were heavier than control by 166, 183 and 180 g, respectively. A quadratic ( = 0.03) effect was observed for breast yield in response to SB. There was a quadratic reduction ( < 0.05) in gamma-glutamyl transferase (GGT) and a linear increase in glutamate dehydrogenase (GDH) in response to SB. Supplemental SB linearly reduced ( ≤ 0.04) the relative abundance of phylum and , and increased the abundance of phylum (linearly; = 0.02) and (quadratically; = 0.03). 4. The data indicated that the optimal inclusion for SB was between 5 and 10 g/kg for improved growth performance and breast yield. However, increased abundance of and actinobacteria in the caecal digesta suggested that the higher doses enhanced prebiotic effects of seaweed components.