How Cereal Milling Affects Efficiency and Health in Pigs

Cereal milling has great impact in pig health and production costs. Pig feed costs account for 65-80% of total production costs (Jensen, 1976). This has led producers to take advantage of feed manufacturing practices to maximise the use of raw materials.

Properly managed, the increase in the cost associated with the manufacture of feed translates into an improvement in the performance of pigs.

Good manufacturing practices are essential to ensure a low cost-benefit ratio.

Not only is it important to fully understand each processing method and its effects, but you also need to understand how processing influences:

• feed handling characteristics
• production costs
• the digestibility of nutrients and energy
• and pig yield

Grains are the main ingredient in pig feed susceptible to grinding. Other ingredients are pre-processed and arrive at the feed mill under acceptable conditions.

There are two types of mills commonly used to reduce the particle size of ingredients, roller mills and hammer mills.

Roller mills

Roller mills reduce particle size by crushing or grinding, thanks to the application of a compressive force on the ingredient.

This process produces a small amount of fine material resulting in a relatively uniform particle size of the grain.

Hammer mills

Hammer mills reduce the particle size of ingredients by impact grinding (Pfost, 1976), resulting in particles with a more spherical shape and increasing the amount of fine, pulverized particles, resulting in a less uniform particle size (Koch, 2002).

Previous studies have shown that the increase in the amount of non-uniform particles generated by the use of hammer mills results in a greater angle of fall, which translates into a worse fluidity (Groesbeck et al., 2006).

Costs asocciated with milling

On the other hand, in addition to reducing handling characteristics, grinding grains increases the costs associated with milling. These costs include:

The initial cost of equipment may seem expensive, but depending on the mill, energy costs for a year may exceed the costs of a new piece of grinding equipment. Understanding the variety of factors that influence the efficiency and production rate of milling can be very beneficial for feed manufacturers.

Some data shows that reducing the particle size of cereal grains leads to increased energy requirements and a reduction in the production rate (Gebhardt et al. 2018).

The rate at which these factors change can be altered by:

• the grain
• the type of mill
• grinding parameters
• and the maintenance of the mills

Roller mills and hammer mills have different operating costs and require different levels of investment

Considering the negative effects of particle size reduction on milling efficiency, it is important to further investigate whether these losses are justified by improvements in animal performance.

The idea of reducing the particle size of grains before feeding pigs with them came about in the early 30s.

• Grains have a protective outer layer that makes it difficult for digestive enzymes to access all of its nutrients.
• Reducing the particle size of grains through milling exposes protected areas to the action of digestive enzymes, allowing the pig to digest a greater portion of nutrients.
• Fraps (1932) used ground sorghum to show that reducing particle size improved the digestibility of nutrients.
• Aubel (1945, 1955) continued to work on this idea, demonstrating improvements in feed efficiency when pigs were fed ground corn and sorghum grains.