Starch is the primary energy source in livestock diets and constitutes up to 50% of poultry diets. Starch is largely supplied by cereal grains and in the U.S., specifically corn. Much research has been dedicated to evaluating grain processing methods that increase starch availability, such as grinding and thermal processing1-4. The purpose of these processing methods is to disrupt the outer shell of the corn kernel and expose the starch endosperm to make it more accessible for enzymatic digestion in the animal. Starch digestion is largely driven by amylase, a glycolytic enzyme that degrades starch into sugars. Therefore, grain processing can improve starch digestion by increasing the surface area of starch molecules and providing more substrate for amylase to bind.
Enogen® Feed corn (EFC) is a corn variety which contains a bacterial transgene that produces an -amylase enzyme5. Originally developed to improve the efficiency of ethanol production, recent studies have revealed potential benefits in animal performance when EFC is included in livestock diets. Increased amylase activity of EFC corn is designed to assist in the rapid degradation of starch to sugars, thereby providing more available energy for growth. Research has shown a 5% increase in feed efficiency and a 4.1% increase in starch digestion when conventional corn is replaced by EFC in the diets of stocker and finishing cattle5. An experiment in swine revealed a tendency for improved average daily gain for pigs consuming EFC compared to conventional corn during the last 82 days of the finishing period6. Evaluation of EFC in poultry diets has not yet occurred.
Effects of EFC on feed processing characteristics are also of interest. It is currently unknown how a corn variety with high amylase may react in the pelleting process. Pelleting requires addition of heat and moisture in the form of steam. Steam is typically mixed with mash feed in the steam conditioner for 15-30 sec but can be retained up to 120 sec depending on equipment and processing parameters. Pressure is then applied to the steamed feed mixture as it is pressed through the pellet die. The combination of moisture and frictional heat increases starch gelatinization, which is an irreversible process that leads to greater starch availability7; thus, the amylase activity in EFC would be expected to further increase the degree of starch gelatinization in pelleted feed.
This experiment was designed to discover the effects of corn type and conditioner retention time on pelleting characteristics of a poultry diet and subsequent broiler growth performance and carcass traits. Research in this area will help to uncover beneficial effects of EFC in broilers that many researchers were not able to explore. Thus, a new theory on broiler efficiency due to feeding a high-amylase corn variety may be arrived at.
MATERIALS AND METHODS
This research was conducted according to the experimental protocols approved by the Institutional Animal Care and Use Committee at Kansas State University.
Twelve hundred male broiler chicks (Cobb-Vantress, Siloam Springs, AR) were used in a 45-d randomized complete block experiment with treatments arranged as a 2×2 factorial, with factors consisting of corn source [conventional (CON) and EFC] and conditioner retention time (30 and 80 sec). Corn was ground to 700 μm in the starter phase and 900 μm in the grower and finisher phases using a hammermill (Bliss, Model 22115). Starter, grower and finisher broiler diets were mixed in a 907 kg Hayes and Stolz horizontal counterpoise mixer (Table 1). For treatments containing EFC, conventional corn was replaced by EFC on a kg:kg basis.
For the pelleting trial, diets were steam conditioned (Wenger twin staff pre-conditioner, Model 150) for 30 or 80 sec at 75°C and subsequently pelleted using a 30-horsepower pellet mill (1012-2 HD Master Model, California Pellet Mill) equipped with a 4-32 mm pellet die. Production rate was set at 10 kg per min, approximately 65% of the rated throughput for the pellet mill. Pelleting of the starter, grower and finisher diets provided three replications for each treatment; therefore, diet served as the blocking factor. Conditioner retention times were calculated by adjusting the conditioner screw speed and dividing the amount of feed in the conditioner by the production rate. For each run, a conventional corn-soybean meal flush diet was used to warm the mill up to 75°C, the first treatment was pelleted and the mill was shut down to allow the pelleted feed to cool and to adjust conditioner screw settings for the next treatment. Conditioning temperature, hot pellet temperature (HPT) and production rate were recorded at 3 time points during each run (Table 2). Pellet mill amps and volts were also monitored throughout each run to calculate energy consumption.
Prior to pelleting, a total of 10 mash samples per treatment were collected for analysis of soluble starch. During each processing run, 3 conditioned mash and 3 pellet samples were collected throughout the run. Conditioned mash samples were immediately analyzed for soluble starch and pellets were immediately placed in an experimental counter-flow cooler for 10 min. Once pellets were cool, they were analyzed for soluble starch and pellet durability index (PDI).
For the performance trial, chicks were maintained on a 24 h lighting schedule in a thermostatically controlled room with ad libitum access to feed and water. Chicks were housed in 1.2×2.4 m floor pens with 7-10 cm of pine shavings. Each pen was fitted with single hanging feeder and 4 nipple waterers. Chicks were randomly allocated to groups of 15, weighed and randomly assigned to 1 of 80 floor pens. Treatments were randomly assigned to pens and blocked by location for a total of 20 replications per treatment. Chicks were fed a common diet from 0-4 days of age before initiation of the experiment. Therefore, day 0 of the experiment corresponded with 5 days of age for the chicks. A starter diet was fed from study day 0-10, a grower diet from day 11-24 and a finisher diet from day 25-45. In the case of mortality, chick weight, feeder weight, treatment and pen number were recorded. Pen weights and feed consumption were measured on day 11, 25, 39 and 45 for calculation of body weight gain, feed intake and feed efficiency (Table 3). Additionally, half of the chicks from each treatment were harvested on day 39 and the remaining half were harvested on day 45 for determination of carcass weight and dressing percentage (Table 4). Data were analyzed using the GLIMMIX procedure in SAS 9.4 with pen as the experimental unit and pen location as the blocking factor. Main effects included corn type and conditioner retention time. Results were considered significant if p≤0.05 and were considered marginally significant between p>0.05 and p≤0.10.