The Importance of Pellet Quality In Hog Feeding

Livestock Update, September 1998

Allen Harper, Extension Animal Scientist, Swine, Virginia Tech Tidewater AREC

The technology for pelleting livestock and poultry feeds has been around for many years. In general, processing complete swine or poultry feeds into pellets involves preconditioning the total mixed diet with steam followed by extrusion of the mash through a pellet mill die. The newly formed pellets are then cooled and transported for storage and feeding either in bags or bulk. The advantages of feeding growing pigs pelleted diets over standard meal form diets are well documented. These include better feed efficiency, greater starch digestibility, less feed waste, less "sorting" of diet ingredients by pigs, and less segregation of diet ingredients during feed handling. Naturally these advantages come at a cost. The additional cost of pelleting compared to meal form diets can vary from $3.00 to $7.00 more per ton of finished feed. Swine producers that have the option to purchase or manufacture pelleted feeds are thus faced with an important question; are the advantages and added returns of pelleted diets worth the added cost? The most economically important of these added returns would be better feed efficiency. For example if pelleting grower-finisher feed results in a 5% improvement in feed efficiency (less feed per unit of gain), then the justifiable cost increase for pelleting would need to be no more than 5% per ton.

Most of these advantages, particularly as related to growing-finishing pigs, assume that feed pellets are of good "quality." Good quality is a broad term but most notably it refers to the milling of pellets that are dense and durable enough to withstand extensive mechanical handling without compromising the nutritional value of the diet. Factors that contribute to pellet quality in the milling process include proper steam preconditioning with the appropriate amount of heat and moisture, adequate preconditioning time, and production speed at the pellet mill. Feed ingredients also play a role. For example diets, containing some wheat usually result in a more durable pellet. Diets containing high levels of added fat (greater than 6%) increase pellet production speed but tend to form a less durable pellet. Pelleting aids such as montmorillonite clays and lignin sulfonate products may also be added to the diet to enhance pellet quality.

By the time pellets reach the trough of standard self-feeders for pigs, poor quality pellets will start to crumble apart with fine particles of feed separating from the intact pellet. The pigs will tend to selectively feed on intact pellets while allowing build-up of these "fines" in the feeder trough. These fines will adsorb moisture from humid air and from pig saliva, eventually becoming musty and unpalatable. Excessive build-up of fines in the feeder trough leads to rooting and feed waste by the pigs and to blockage of feed flow into the feeder trough.

A recent study reported at the 1998 American Society of Animal Science meetings provides some measure of the negative impacts associated with poor pellet quality. Swine researchers Tim Schell and Eric van Heugten (at the Univ. of Georgia and North Carolina State, respectively) conducted two trials using grower pigs with dietary treatments designed to simulate four levels of pellet quality. In the first trial two hundred feeder pigs weighing 43 lbs. initially were fed under commercial conditions for seven weeks. Their pelleted diets contained 2.5%, 13%, 35%, or 40% "fines." The second trial was identical to the first except that final diet fines content was 3%, 12%, 23%, or 37%. Trial 1 was conducted in November and December and trial 2 in June and July. The different levels of fines in the diets were created by grinding the pelleted control diet (only 2.5 to 3% fines) to a particle size of 830 microns followed by adding specific amounts of this fine material back to the pelleted control diet. In this manner the researchers simulated different levels of pellet quality and fines content in the test diets without changing ingredient or nutrient content.

There were differences in the performance of pigs fed the different diets. Rate of gain tended to be poorer for pigs fed the diets higher in fines content. However, feed disappearance, which includes feed consumed and feed wasted, also tended to be greater as the amount of fines in the diets increased. These two factors combined resulted in a significant negative impact of increased fines content (i.e. lower pellet quality) on pig feed efficiency.

Pellet quality effects on feed efficiency in growing pigs¹

Nov./Dec. trial		June/July trial
% of "fines"	lbs. feed/lb. gain	% of "fines"	lbs. feed/lb.gain
2.5%	1.922	3%	2.013
13%	1.94	12%	2.08
25%	1.98	23%	2.09
40%	2.00	37%	2.10

¹ Adapted from Schell and van Heugten (1998), J. Anim. Sci. 76(suppl. 1):185.
² Linear depression in feed efficiency with increasing level of "fines" (P<.05).
³ Low "fines" diet significantly better feed efficiency than other diets (P<.05).

This work demonstrates that much of the performance advantage associated with pelleted grower-finisher swine feeds can be lost if pellets are of poor quality and contain a significant quantity of "fines." For producers purchasing or manufacturing pelleted feeds, this translates into a direct increase in the expected cost of gain. Contract feeders with payment schedules that include feed efficiency provisions can also be impacted by pellet quality. If pellet quality is poor it can reduce the opportunity that the producer has to receive feed efficiency bonuses in addition to the base payments for contract fed market hogs.

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