Abstract: The objective of the current study was to investigate the effects of an algal β-1,3-glucan (ABG) product on broiler performance, oocyst output following an Eimeria challenge and antibody titer levels following a Newcastle Disease vaccination program. Three experiments were conducted evaluating four dietary treatments: a control diet and three levels of ABG (100, 250 and 750 g/MT). Experiment 1 evaluated the effects of ABG on performance parameters and relative organ weight in a 42 d grow-out study. Ten replicates per treatment each contained 35 live-oocyst vaccinated broilers. Inclusion of ABG at 750 g/MT increased d 14 BW compared to the control while inclusion of ABG at 250 g/MT improved feed conversion ratio (FCR) compared to the control diet during the starter phase of production. At the conclusion of the trial, no differences in BW, FCR, or relative organ weights were observed. Experiment 2 consisted of 70 broilers per dietary treatment placed in battery pens and challenged with a 100 x dose of vaccine strain Eimeria oocysts on d 10. Fecal samples were collected on 6, 7, 8 and 9 d post inoculation to determine oocyst output. Inclusion of ABG at 100 and 250 g/MT numerically reduced oocyst/g of fecal material on d 6 post-challenge compared to the control. The inclusion of ABG at 250 and 750 g/MT reduced cumulative FCR through d 20 compared to the challenged control broilers. Experiment 3 consisted of 120 male broilers with 5 birds randomly placed in each of 6 replicate battery pens per treatment. Newcastle vaccine was administered on d 1 of age and a boost was administered on d 18 of age. Blood samples were collected 7 d post boost to evaluate Newcastle specific antibody titers. Greater antibody titers were observed on d 25 in birds fed ABG at 250 g/MT compared to the control group. Combined, these data demonstrate the ability of ABG to stimulate broiler immune response and improve early broiler performance during coccidial vaccine challenge.