The reduction of antibiotic growth promoter (AGP) use in broiler feed resulted in necrotic enteritis (NE) emerging as a common broiler disease worldwide. In this study, two trials with feed additives and combinations thereof were tested against an AGP (Zinc Bacitracin). In the first trial, broilers were raised in a non-challenged environment and in the second trial, broilers were predisposed to conditions which led to the development of NE. The key risk factor for the development of NE is an intestinal environment that favours the growth of the organism Clostridium perfringens. Day-old, male Ross 308 broilers were randomly distributed in an environmentally controlled broiler house, with 12 replicate pens per treatment and 23 birds per pen at the start of each trial. Treatment diets were fed from day 0 for a 35 day grow-out cycle. Apart from a negative control (no feed additives) and a positive control (AGP), three additional treatments were included for each trial. In the first trial, the feed of the first treatment was supplemented with a mixture of essential oil (EO) compounds (Biacid Nucleus, Provimi). In the second treatment a direct fed microbial (Bacillus subtilis; DFM) was added to the feed, while a prebiotic (Mannoseoligosacharide, Provimi) was added to the third treatment. When given in combination with AGP, the alternative feed additives resulted in longer duodenal villi (1990.79 μm vs 1876.35 μm) and ileal villi (790.6 μm vs 713.96 μm) than when given alone. However, the alternative feed additives under non-challenging conditions showed no direct increase in performance when given alone or in combination with AGP. In the second trial, the first treatment consisted of a direct fed microbial (Bacillus subtilis; DFM), while a blend of essential oil compounds and organic acids (Biacid, Provimi) were added to the second treatment. The feed of a third treatment was supplemented with a mixture of essential oil compounds (Biacid Nucleus, Provimi) and DFM. At 10 days of age, birds received a coccidial vaccine (Immunocox, Ceva) at 10x the prescribed dosage and on day 14 they were orally inoculated with Clostridium perfringens. The birds that received Biacid were significantly (P ≤0.05) heavier at 28 days of age compared to birds from the negative control group (1438 g vs 1385 g). Although body weight of the broilers at 35 days of age did not differ significantly (P >0.05) between treatments, feed conversion ratio (FCR; g feed intake/g body weight gain) over the rearing period was significantly (P ≤0.05) lower for broilers supplemented with Biacid (1.83) compared to broilers in the negative control (1.94). Broilers that received the AGP had an FCR of 1.87, while broilers from the DFM and DFM plus Biacid Nucleus treatments had FCRs of 1.87 and 1.84, respectively. The NE scores of broilers supplemented with Biacid and Biacid Nuclease was significantly (P ≤0.05) lower than the NE scores in broilers from the negative control group. It was concluded that Biacid, a combination of essential oils and organic acids, improved performance of broilers that were subjected to conditions favouring the development of NE in broilers.
Dissertation (MSc (Agric))--University of Pretoria, 2019.