It is generally accepted that birds perform better when fed good-quality pellets; however, achieving pellet quality at any cost may not be the best strategy. It is important to consider some of the more recent research regarding interactions between feed processing, feed additives and modern genetics before determining the best pellet quality for your operation.
Directing energy to growth
Performance of modern broilers improves when caloric density is increased by the addition of fat, and performance also improves when a higher proportion of pellets are present at the feeder. Researchers at Oklahoma State University (McKinney, 2004) first fed broilers varied levels of fat to develop a mathematical model describing the relationship between energy and growth. In a second trial, energy was kept constant and the percentage of pellets at the feeder was varied. The performance response was then used to calculate the effective caloric value associated with each proportion of pellets (Figure 1). Increasing the proportion of pellets from 0 percent to 100 percent increased ECV by 187 Mcal/kg. This increase was most likely due to reduced maintenance energy; birds spent more time resting and less time eating (Figure 2).
Testing continued with two different strains of birds (Skinner-Noble, 2005). In this case, the feed form was simply mash versus pellets. The increase in ECV was 111 Mcal/kg for Strain A and 189 Mcal/kg for Strain B. Time spent resting and eating was also observed. Results suggest that different strains may respond differently to pellet quality (Figure 3).
Fast growers, slow growers
Researchers at Institut National in Paris studied the importance of pellet quality with slow- and fast-growing broilers (Quentin, 2004). The results were very interesting. Slow-growing broilers were less responsive to pellet quality. In contrast, when presented with a higher proportion of pellets, fast-growing broilers ate more, gained more and had better feed conversion. Quentin said that selection of genetics for fast-growing chickens “has led to lazy birds that have reduced their level of physical activity.” The fast growers are “couch potatoes”; when they make the occasional effort to go to the feeder, they can eat more feed as pellets than as mash. Slow-growing chickens are more active and make multiple trips to the feeder. Results for fast growers indicate that the feed-conversion ratio increased rapidly when the proportion of pellets fell below 50 percent and growth retardation began when pellets fell below 80 percent (Figure 4). Data was collected between day 19 and day 23.
Pellet durability and bird performance
Researchers in Germany fed birds mash, poor-quality pellets and good-quality pellets (Lemme, 2006). Pellets of poor and good qualities had Holmen durabilities of about 85 percent and 25 percent, respectively. The term “pellet durability” is used to describe the ability of the pellets to survive transport to the feeder without losing their physical form. Birds fed poor-quality pellets had the same performance as birds fed mash, while good-quality pellets resulted in a significant increase in gain.
Increasing the level of mechanical energy is one option for improving durability. Tests in Israel investigated the effect of the pelleting degree on broiler performance (Nir, 1994). Chickens ate identical formulations supplied as mash (PD-0), pellets (PD-1) or double-pelleted (PD-2). Kahl hardness levels were 4.9 and 8.0 for PD-1 and PD-2, respectively. Birds fed pellets spent more time resting and had higher levels of abdominal fat, consistent with the idea of conservation of maintenance energy. However, both feed intake and gain declined with double-pelleted diets. It was suggested that the birds may have found the pellets to be excessively hard.
Improving pellet durability
In a separate study where double-pellets were reground to remove the hardness factor, bird performance with double-pellets fell below that of the starting mash (Shipe, 2011). Frictional heating increases with extended mechanical processing, i.e., double-pelleting or use of expanders, and may degrade some nutrients, thereby reducing the improvement in bird performance that should accompany better pellet durability.
Pellet durability can be improved by shifting fat away from the mixer and applying it as a coating onto the finished pellets. Researchers at West Virginia University recently studied the impact of changing the level of mixer fat (Gehring, 2011). Feed was mixed with or without supplemental enzymes and with three levels of mixer fat; 1.0 percent, 2.5 percent and 4.0 percent. Feeds were conditioned to 82C and 85C and pelleted. All feed was then reground to eliminate pellet quality as a factor. Fat was added post-pelleting to make the diets iso-caloric. The best feed conversion and lowest abdominal fat pad occurred when pellets were conditioned to 85C with 4 percent mixer fat and contained supplemental enzyme.
Researchers had previously found the increasing mixer-added fat to 3 percent, in combination with 0.5 percent lignosulfonate, improved the digestibility of several amino acids, including lysine (2011, Moritz). In the current study, they speculated that reduced frictional heating through the die helped to maintain nutrient availability and prevent denaturation of the enzymes, which could then release previously unavailable nutrients.
Use of lignosulfonate
Lignosulfonate is a natural polymer that is known to be effective as both a binder and a lubricant in poultry diets (Pfost, 1976). West Virginia University researchers included lignosulfonate in a 2-by-2 factorial experiment that used normal or high Amino Acids Density and two pelleting techniques: 1 percent mixer-added fat plus sand or 3 percent mixer-added fat with 0.5 percent lignosulfonate. Diets were crumbled and fed to turkey poults from d-10 through d-39. The highest average poult weight resulted from diets with High Amino Acids Density, 3 percent mixer fat, and 0.5 percent lignosulfonate binder (2011, Moritz). Researchers in New Zealand similarly saw improved performance in broilers with pellets containing binder (2011, Ravindran).
Improving pellet durability generally improves bird performance. Steam conditioning to >80C improves pellet durability and has additional benefits. Increasing mechanical force by reducing mixer-added fat, increasing die thickness, or double-pelleting will improve durability, but the associated frictional heating may have a negative impact on heat-sensitive feed components and subsequent bird performance. Conditioning to >80C, adding >2 percent fat at the mixer, and formulating for pellet quality, including the use of commercial pellet binders, may provide the best combination for efficient manufacturing and optimum bird performance.