Most of the world?s broiler rearing is based on routine use of coccidiostats (as feed additives) suppressing unicellular parasites (coccidia/coccidiosis) and small intestinal bacterial overgrowth
of Clostridium perfringens (including necrotic enteritis). At the time Norway is probably the only country whose entire broiler industry has abolished the use of coccidiostats. Other health-promoting and disease-preventing measures become very important when broilers are kept this way. The main aim of this research project is to provide new knowledge contributing to good broiler health and efficient use of resources during rearing of broilers without coccidiostats.
The problem was approached in three different ways:
1. Testing of alternative feed additives to anticoccidials in experiments:
The testing of alternative feed additives evaluated additive categories (phytogenics, organic acids, prebiotics and probiotics) as well as active components in the commercially available test products. We studied effect on Clostridium perfringens, if the broilers were able to utilise the feed efficiently, and how body weight gain was affected. The results indicate that the most efficient of these alternatives to coccidiostats were comparable to the coccidiostat narasin regarding weight gain and a little poorer regarding feed conversion ratio and Clostridium perfringens counts. Although none of the tested products equalled narasin in terms of collective performance with regard to all three outcome variables, our results indicate that the best-performing products do represent valuable contributions to a sustainable farming of broilers without routine use of coccidiostats. Prebiotics and probiotics had the overall best performances during coccidia challenge, phytogenics improved overall feed conversion and reduced counts of the intestinal bacterium Clostridium perfringens, and organic acids increased weight gain independent of age. Performances of products within the same additive category varied substantially, indicating the importance of specific active compounds and component combinations.
2. Experimental testing of the effect of dietary starch level on gastrointestinal health, digestibility
and production performance:
Most of the energy and nutritional building stones the broilers can extract from their feeds originate from starch, fat and proteins. Starch usually constitute the greater part and fat usually the smallest part. Our aim was to find out if two different levels (45 % vs 23 %) of dietary starch had an impact on intestinal health, digestibility and production performance. Additional starch in the diet with 45 % starch was provided as isolated starch. Removed starch in the low-starch diet was replaced by dietary fat (1.4 % vs 9.5 %) and quarts sand (16 %) to achieve the same levels of proteins and energy. Both treatment groups were challenged with coccidia, which induced peak oocyst excretion at 21-23 days of age. Our hypothesis was that the feed with 45 % starch would induce impaired digestibility, production results and intestinal health, compared to the diet with 23 % starch. The results indicated that the feed with 45 % starch was associated with higher starch digestibility and improved feed conversion than the diet with 23 % starch. The occurrence of necrotic enteritis was similar in the two diet groups. The feed with 45 % starch gave a gradual increase in the length of intestinal villi from 16 to 29 days of age. In contrast to this, the villus length among broilers offered feed with 23 % starch peaked at 21-23 days of age, which concurred with peak oocyst excretion. And the 23 % starch group had lower villi than the 45 % starch group at 29 days of age. These findings demonstrate the capacity of broiler chickens to digest a diet with 45 % starch. More work is needed to clarify if this capacity depends on starch source. The results also indicate that dietary starch level influenced the dynamics of villus length, and therefore also the mucosal surface area, of the anterior small intestine. A possible hypothesis based on these findings is that high levels of dietary starch induce an increased mucosal surface area of the anterior small intestine, which may make the birds more resilient to coccidial infections in this gut segment.
Prosjektet har styrka samarbeidet mellom fjørfeforsking ved NMBU og Veterinærinstituttet, og dermed gitt eit godt utgangspunkt for vidare arbeid på dette feltet på nye Campus Ås.
Prosjektet gav fagleg støtte til norsk slaktekyllingnæring i overgangsfasen til oppdrett utan rutinemessig bruk av koksidiostatika i fôret.
Prosjektet har styrka det faglege grunnlaget for stabilt god dyrehelse og dyrevelferd og eit svært lågt antibiotikaforbruk i norsk slaktekyllingoppdrett.
The Norwegian poultry industry would prefer to abolish the use of in-feed anticocidials in conventional broiler rearing, and needs a firm knowledge base in order to decide whether an abolishment is sustainable or not. The Norwegian Veterinary Institute, the Norwegian University of Life Sciences and Ghent University in close collaboration with the industry propose a 4-year project in which the knowledge needed can be achieved.
The problem is approached in four different ways:
1. Testing of alternative products to anticoccidials
2. Prebiotic stimulation of beneficial butyrate-producing intestinal bacteria
3. Dietary manipulations aimed at reducing the risk of intestinal proliferation of detrimental bacteria
4. Evaluating the role of practically relevant in-feed levels of the mycotoxin deoxynivalenol as a predisposing factor for gastrointestinal health problems
The work with these major research questions is based on broiler experiments. Intestinal counts of Clostridium perfringens will be used as an important outcome variable in the experiments, because this bacterium is an indicator of gastrointestinal health problems and growth depression. Tested alternative products will be ranked on the basis of an efficacy score based on important outcomes, including production performance,Clostridium perfringens counts and foot pad scores.
Based on results from the experimental work and economic considerations, an alternative treatment to anticoccidals will be chosen for testing in a major intervention study in commercial broiler flocks. Important outcome variables in the field study include production results, foot scores as a welfare indicator, and frequency of clinical disease requiring use of therapeutic antibiotics. The results of this field study are expected to provide a basis for recommendations regarding the future use of anticoccidials in conventional broiler rearing in Norway.