A cross-study analysis of the effect of a dual-strain probiotic applied via the waterline on the growth performance and gut health of broilers under a mild necrotic enteritis challenge

Probiotics offer potential as an approach for the prevention and control of poultry intestinal diseases, but external factors can influence the birds' response. Combining data from multiple trials provides greater confidence around efficacy under varying production conditions. Therefore, this study combined data from three separate trials analyzing the effect of a dual-strain probiotic comprising Lactobacillus acidophilus AG01 and Bifidobacterium animalis subspecies lactis AG02 on broilers during a mild necrotic enteritis (NE) challenge. In each, 1,440 broilers were assigned to floor-pens (40 birds/pen, 12 pens/treatment) in a completely randomized design. Treatments in each trial were a non-challenged control (C); challenged control (10 x dose of Eimeria/bird on d 14 and 1.0 x ∼10⁹ colony forming units (CFU)/bird of C. perfringens on d 16-20; CC); and CC supplemented daily via the waterline with 1 × 10⁹ CFU/bird of probiotic (CC+Probiotic). Birds were fed corn-soybean mealbased diets by phase (starter: 0 to 14, grower: 15 to 28, finisher: 29 to 42 d of age) ad libitum. Growth performance was monitored over 42 d, NE lesion scoring performed on d 21 and 28 in all trials, and, in Trial 3 only, cecal microbiota composition was analyzed on d 28. From d 1 to 42, CC birds exhibited reduced BW, BW gain (BWG), and feed intake (FI) (-9.2 %, -9.5 %, -5.0 %, respectively; P < 0.05), increased FCR and mortality (+8.5 points and 1.3 % points, respectively; P < 0.05) compared to C, and increased NE induction on d 28 (67.8 vs. 9.4 %, P <0.05). Compared to CC, CC+Probiotic birds exhibited increased BW, BWG and FI (d 42: +6.9 %, +7.1 %, +4.0 %; P < 0.05) and reduced FCR, mortality and d 28 NE lesion scores (-0.5 points, -1.4 % points and -57.1 %, respectively; P < 0.05). The composition of the cecal microbiota of CC+Probiotic birds at 28 d of age exhibited higher abundance of butyrogenic bacterial genera in Trial 3, which may have contributed to the beneficial effects of the probiotic. The results demonstrate that the probiotic ameliorated the negative effects of a mild NE-challenge on growth performance and intestinal symptoms over three trials incorporating variation in season and bird breed.