Particle Size in Swine Diets

[mikey]

Particle Size in Swine Diets
Reducing particle size of the grower-finisher from an average of 1000 microns to an average of 700 microns could save about $1.78 per pig per annum. An investment in a few particle size tests per year is well worth the effort, explains Greg Simpson, swine nutritionist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) in the December 2008 issue of Pork News and Views.

 

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. However, 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 non-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 90kg 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 60-90 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/tonne, 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.

November 2008

[mikey]

Extra water in mixer gives better pellets
// 10 dec 2008

Scientists from Norway (Felleskjøpet Fôrutvikling and Norwegian University of Life Sciences) and the US (Kansas State University) have added extra water to the mixer prior to steam conditioning to study the effects on pellet quality of pig feeds.
 
Two diets for finishing pigs were used to determine the effect of adding water into the mixer on processing characteristics and pellet quality.

The researchers used a barley-based diet and a maize-based diet. Both diets were produced without and with use of an expander.

Adding up to 120 g water/kg into the mixer prior to steam conditioning and pelleting of the barley-based diet, improved pelleting efficiency, pellet durability index (PDI) and modified PDI (with five hexagonal nuts added into the tumbling box), by 15, 10 and 10%, respectively.

When water was added into the mixer prior to expanding the barley-based diet, PDI increased from 93 to 95% and modified PDI from 91 to 94%.

The maize-based diet was processed with motor load held constant to maximize feed mill output, and production rate held constant to minimize energy use.

At a constant motor load and a constant production rate, adding up to 30 g water/kg into the maize-based diet prior to steam conditioning increased pelleting efficiency by 22% and 9%, PDI was improved from 84 to 89% and from 79 to 87%, respectively.

Expander conditioning of the maize-based diet increased PDI from 92% at none to 94% at 30 g/kg water addition.

Correspondingly, modified PDI was increased from 89 to 93% at adding none and 30 g water/kg into the mixer prior to expander conditioning.

The overall conclusion from the experiment was that adding water into the mixer before steam conditioning improved pelleting efficiency and pellet quality in barley- and maize-based diet for finishing pigs.