Pelleting of feed has many positive attributes, according to Charles Stark, Professor in Feed Technology at Kansas State University, the US.
He explained that this is of special importance when it comes to dealing with ingredients that have poor flow characteristics and low bulk density. Pelleting feed with these ingredients can improve feed intake and thus FCR.
Improving pellet quality has a direct impact on FCR and whilst measures taken to improve quality can add to costs, as feed prices increase and feedmillers opt for more alternatives to manage costs, Prof Stark said this provides the incentive to invest in higher quality feed with fewer fines (that is greater percentage of pellets in the feed).
Better pellets mean, reduced wastage, improved palatability, and improved nutrient utilization due to heat treatment.
Improving pellet durability
One way to improve pellet durability is adding steam to the feed to increase moisture and temperature of the mash to 16-18% and 80-85 degrees respectively. This would mean more time spent in the conditioner. Prof Stark recommends between 45-60 seconds as the ideal time in conditioner.
The flipside of this however is that high temperatures can denature enzymes in feed, thus lowering its nutrient value. This is especially important when using alternative ingredients which need enzyme action to remove anti nutrient factors from feed.
Prof Stark explained that whilst traditionally it was thought that heat was mainly generated from the conditioning process, latest research has shown that enzyme stability can also be impacted by frictional heat caused in the die and roller as well as by the final temperature of the hot pellet.
Frictional heat in the die and roller in turn is dependent on the thickness of the die and the production rate (slower rate means longer time in the chamber and thus greater heat).
The pellet die specifications also determine the diameter of the pellet and how long the pellet is held under compression and exposed to heat.
“So, you might be having a conditioner temperature of 79.4 degrees, but the pellet may come out with a temperature of 85 degrees because of the die used,” said Prof Stark.
Thus, a fine balance must be struck between getting the best pellet quality possible and maintaining a temperature at which there is minimal denaturation of enzymes. The latter can affect FCR and nutrient stability of the feed, stressed Prof Stark.
Pelleting with alternatives
Prof Stark describes three things that need to be taken into consideration which can affect pellet quality when using alternatives. They are conditioning (time, moisture levels, and temperature), formulation (fat in mixer vs fat in ingredients, source of ingredients, and particle size) and the pellet die (specification and condition of die rolls).
When it comes to formulation, crude protein (CP) content and by products generated by alternatives can affect hardness of the pellet. “Increasing CP as well as temperature has shown to improve the pellet durability index (PDI),” said Prof Stark.
Ingredients which cause larger size particles can cause fractures in pellets, leading to more fines, and lower feed quality. “In addition, too much fat in the mixer can affect quality. And this is important when using alternatives with low fat content and you need to add oil into the mixer or post pelleting,” he explained.
With the die and roller, different formulations will require the right specification of die to get the required pellet quality. Prof Stark noted that if feedmillers using alternatives are not getting the feed throughput they want, they need to check if they have the right die for the job.
Finally, moisture, whether it is the quantity added to the conditioner or the moisture content in the pellets coming out of the conditioner, both have an impact on pellet quality. The amount of moisture needed however would depend on the alternative used.
“If you are adding moisture into the conditioner and maintain the temperature needed, you need to ensure you have enough cooling capacity thereafter to remove any excess,” said Prof Stark.