The purpose of the study was to evaluate the benefits, if any, of adding a probiotic product containing Bacillus subtillus to the diet of broilers. The study was conducted in an open-sided house, with curtains and a coal boiler (HEATCO) attached to a heat sock. The house contained 64 pens in total, divided into 2 rows of 32 pens each over the length of the house. The pens were covered with used chicken litter (4cm deep). Three thousand six hundred Ross 308 broiler birds were feather-sexed and randomly distributed throughout the pens, 60 broilers of the same sex per pen at a stocking density of 20 birds/ m2. All broilers received similar typical South African maize-soya diets throughout the study. Diets were treated with antibiotic growth promoters (AGP) and / or direct-fed-microbials (DFM) to create six treatments as follows: Negative Control: Basal diet (without AGP), Positive Control: Basal diet (with AGP), DFM at 500g/ton (without AGP), DFM at 250g/ton (without AGP), DFM at 500g/ton (with AGP), and DFM at 250g/ton (with AGP). Broiler performance was measured weekly in terms of body weight (BW), feed intake (FI) and feed conversion ratio (FCR) from day old to 35 days of age. Birds were culled at day old, as well as 22 days of age for the isolation of Avian Pathogenic E. coli (APEC), E. coli and Lactobacillus from the gastrointestinal tract.
Males showed a higher feed intake from 14 to 35 days of age compared to females, even though the FCR remained similar between sexes (P > 0.05). There were no dose response between DFM 500g/ton and DFM 250g/ton, as well as between DFM 500g/ton + AGP and DFM 250g/ton + AGP (P > 0.05) in terms of BW, FI and FCR. Positive Control had a higher body weight, no difference in feed intake and lower FCR compared to Negative Control at 35 days (P < 0.05). A lower dose of DFMs (250g/ton) in the diets of broilers revealed a significantly lower FCR compared to diets without DFMs (Negative Control), and DFM (500g/ton and 250g/ton) + AGP, and no significant difference in FCR compared to DFM (500g/tom) and Positive Control. However, when combining a DFM with AGP in the diet, the FCR of broilers increased due to a lower weight obtained with a higher feed intake at 35 days. The DFM (500g/ton) + AGP had a significantly lower BW compared to Positive Control at 35 days, although, revealed no significant difference in terms of FI (P > 0.05), but a significantly higher FCR at 35 days compared to Positive Control (P < 0.05).
DFM (250g/ton) without AGP tend to lower the feed intake (P < 0.05) of broilers compared to AGPs, but when combining a DFM with AGP, the feed intake increased significantly (P < 0.05), revealing a higher FCR (P < 0.05) compared to AGPs and DFM (250g/ton). The recommendation will be to use a lower dose of DFM (250g/ton) as an alternative for AGP in broiler diets.
Dissertation (MScAgric)--University of Pretoria, 2015.