Particle Size in Swine Diets

With feed equalling 60% to 75% of the cost of producing a pig it is important to get the most out of every feed dollar. Particle size is the term that refers to the average diameter of individual particles of feed or simply the feed's fineness of grind. Since, grain represents the primary energy source in most on-farm mixed diets, producers should be concerned with not only the nutritional quality of the grain but also with how it is processed.

It is well documented that reducing particle size has a great impact on feed efficiency. By increasing the surface area of the grain there is greater interaction of the feed with digestive enzymes, thus improving the digestibility of nutrients. But, the optimum diet particle size is a decision that needs to be balanced between pig performance and feeding/milling efficiencies.

Grinding improves the ease of handling, reduces segregation during feed delivery and increases the uniformity of mixing. Grinding too fine may increase feed bridging and the incidence of keratinisation and/or gastric ulcers. However, it should be noted that the incidence and severity of gastric lesions is also affected by grain type, environmental/social stress, disease and out of feed events. In addition, finer grinding increases feed processing cost and dust levels. In most experiments, a dietary particle size of approximately 700 microns optimizes both pig performance and feed/milling efficiencies.

There are numerous publications that have looked at the effect of particle size on feed efficiency using various grains. Researchers at Kansas State University have found that an appropriate "rule of thumb" for growing pigs is for each 100 micron reduction in mean particle size of corn there is a 1.2 to 1.4% improvement in gain/feed. When this "rule" is applied to various feed costs it becomes easy to see why attention to grinding is economically important (Table 1).

Table 1. Effect of Particle Size on Feed Efficiency and Feed Costs

	Particle Size (a)
Coarse	Medium	Fine
<1000 microns	900 to 700 microns	>600 microns
Gain:Feed	0.333	0.342	0.362
Feed:Gain	3.00	2.92	2.76

Feed Cost/MT	Feed Cost/Pig (b)
$350	$94.59	$92.11	$87.02
$300	$81.08	$78.95	$74.59
$250	$67.57	$65.79	$62.15
$200	$54.05	$52.63	$49.72

^(a) Adapted from Wondra et. al. 1995b. Effects of particle size and pelleting on growth performance, nutrient digestibility, and stomach morphology in finishing pigs. J. Anim. Sci. 73:757.
^(b) Assuming 90 kg gain using on-farm mixed corn, soybean meal, premix diets.

Particle size analysis is a relatively inexpensive test and should be a routine measure incorporated into an on-farm quality control program. Producers should check ground grain or one complete diet at least twice per year and for larger operations up to every 60 to 90 days. There are a number of commercial laboratories that can determine particle size along with several different on-farm use kits. The key areas to look for on the analysis are the average particle size (700 to 800 microns), shape of the graph/curve (bell shaped or normal) and less than 10% percent of the sample being too coarse (>1850 microns) or too fine (<300 microns).

If you market 8000 hogs per year, at an average feed cost of $250/MT, reducing particle size in the grower-finisher from an average of 1000 microns to an average of 700 microns saves about $1.78/pig or $14,240/year. An investment in a few particle size tests per year is well worth the effort.

By Greg Simpson, Swine Nutritionist/OMAFRA
December 2008 Pork News & Views newsletter
Government of Ontario Ministry of Agriculture, Food and Rural Affairs

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Particle Size in Swine Diets