An experimental direct-fed microbial (DFM) was evaluated in a dose- response trial to determine broiler live performance to 42 d with Coccivac® B at placement (d 0), used litter on d 4, and toxin-producing Clostridium perfringens (Cp) challenges on d 17-18 (by oral gavage and via water trough daily). There were 8 dietary treatment groups with 10 replicate pens of 30 chicks each per treatment (2,400 Cobb 500 straight- run chicks total). Economical, low-protein mash feeds were used except in a nonsupplemented challenged (NS-C) treatment from a contemporary study fed crumbles/pellets. Other treatments were: non-supplemented non-challenged (NS-NC); yeast cell wall 250 ppm (YCW); or DFM at 1x104 [Log 4], 3.16x104 [Log 4.5], 1x105 [Log 5], 3.16x105 [Log 5.5] or 1x106 [Log 6] cfu/g feed. Necrotic enteritis (NE) lesion scores (0=normal to 3= severe) were taken using 3 random birds/pen on d 21. Completely randomized design (P≤0.05) was used with Tukey’s HSD test (P=0.05) to separate means. The NE scores were higher for NS-C (2.17) than for NS-NC (0.59) (P=0.028) with YCW and DFM groups intermediate (1.17 DFM Log 4 to 1.47 YCW). Feed conversion ratio (FCR) 0-28 d was higher (P<0.01) for NS-C group than YCW and DFM supplemented diets (statistically equivalent to NS-NC). The 42-d BW were approaching significance (P=0.059) with NS-C (1.580 kg) vs. NS-NC (1.850 kg) with other groups intermediate (1.681 to 1.745 kg). The FCR and mortality- adjusted FCR (MAFCR) were higher for NS-C than NS-NC (P<0.01), and DFM Log 4 and DFM Log 5 to Log 6 improved FCR, and YCW, DFM Log 4 and DFM Log 5 to Log 6 improved MAFCR vs. NS-C. Mortality % from 0-28 d was not different (P=0.40) but from 0-42 d (P=0.013), NS-C was higher than NS-NC (18.06 vs. 4.44%) and improved with DFM Log 4.5 ( 8.00%) or DFM Log 5 (7.67%) with other groups intermediate (8.67 to 10.00%). In conclusion, under Cp challenge, YCW diets improved 0-28 d FCR and 0-42 d MAFCR vs. NS-C, and DFM Log 4 to Log 6 diets improved 0-28 d FCR, and DFM Log 4 and Log 5 to Log 6 diets improved 0-42 d MAFCR vs. NS-C showing effectiveness. The DFM Log 4.5 and Log 5 diets lowered 0-42 d mortality % vs. NS-C indicating efficacy.
Key Words: broiler, Clostridium perfringens, direct-fed microbial, necrotic enteritis, yeast cell wall.