Improving ileal amino acid digestibility and broiler performance with dietary protease and xylanase

Abstract

The use of exogenous enzymes in broiler diets is well documented, and in recent years their popularity has increased. With the rise of the global population leading to an increased demand in animal protein, farmers are forced to increase production with limited resources thus making production efficiency vital and the use of exogenous enzymes imperative. The aim of this project was to determine the effects that exogenous protease and xylanase have on broiler chickens. A digestibility trial with broiler feed containing protease, and a broiler performance trial including xylanase and protease individually and in combination in the treatment diets were conducted.

The digestibility trial was done to determine the effect that various levels of protease have on ileal amino acid digestibility of broilers. Six hundred male broilers were reared until day 17 on the same standard maize-soya diet, thereafter 480 male birds closest to the average body weight were transferred to 60 metabolic cages and randomly divided into six treatment groups with 10 replicates per treatment. The first treatment was a negative control (NC) with no added enzymes and formulated to replicate a typical South African maize soy-based broiler diet. Four treatments used the negative control diet as a base with the addition of increasing doses of a protease product not previously used in South Africa, Kemzyme (Kemin). A fifth treatment was regarded as a positive control diet with the addition of a well-known protease product often used in South Africa, Proact (DSM). The supplementation of protease in broiler diets did not result in significantly (P<0.05) beneficial results in terms of crude protein (CP) and dry matter (DM) digestibility. The CP digestibility is the amount of dietary crude protein which is absorbed by the broiler and not excreted in the animal’s faeces while the DM digestibility is the portion of dry matter which is digested by the broiler for a given amount of feed intake. No dose response was observed as initially predicted. The negative control group either had significantly (P<0.05) better performance than those treated with protease, or the exogenous protease resulted in insignificant differences compared to the NC. The majority of the ileal amino acid digestibilities were not significantly affected by the addition of different doses of protease to the diet.

The performance trial was done with the aim to determine the effect of dietary xylanase and protease both alone and in combination on the production performance of broiler chickens. Two thousand male broilers were randomly divided into one of a total of 11 treatments. A typical maize soya diet was fed to simulate commercial conditions. A positive control (PC) diet was formulated using standard commercial energy and amino acid levels. Three negative control (NC) diets were included either with 0.418 MJ/kg less energy (NC1), 4% lower amino acid levels (NC2) or lower in both energy and amino acid levels (NC3). Three concentrations of xylanase (Xygest HT) were added to NC1, Kemzyme protease was added to NC2 at two concentration levels, as well as Proact protease. Both Kemzyme and Xygest HT were added to NC3 to form the last treatment.

The addition of xylanase showed no clear or predictable benefit on the weekly or cumulative bird performance. During the first three weeks there was little difference between the treatment groups for weekly performance measurements. During the final two weeks of the trial a supplementation of 10 mg/kg of xylanase resulted in a significantly (P<0.05) lower feed conversion ratio (FCR). The FCR assists in determining how efficiently the broilers grow. It is the amount of feed that needs to be eaten in order to gain 1 kg of body mass. The cumulative FCR for the various xylanase treatments was either insignificant or not beneficial throughout the trial. Results for protease supplementation showed no difference between treatments for both cumulative and weekly performance parameters for the first two weeks. The 28d body weight of birds supplemented with 300 mg/ton protease was significantly higher than the NC and the same birds had the highest weekly feed intake from day 28 to day 35. The weekly and cumulative FCR was not impacted by the addition of protease. The cumulative feed intake was significantly reduced with the addition of 200 mg/kg ProAct and 150 mg/kg Kemzyme protease compared to the PC. The combination of xylanase and protease did not result in any beneficial results regarding weekly and cumulative performance parameters. The portion yield of the broilers was not enhanced with the supplementation of dietary xylanase, protease or a combination of protease and xylanase. The dressing percentage of broilers fed 30 mg/kg of xylanase was significantly higher compared to the NC.

This trial suggests that exogenous enzymes should be used with caution as they do not always provide benefits. Enzymes may decrease the performance of an animal or lead to no difference at all when not used in the correct manner or under the correct circumstances. Therefore, careful application of dietary enzymes is suggested.