Dietary energy level

Because higher energy diets contain more calories, less feed is required for each unit of weight gain or per sow per day when a higher energy diet is fed. This is a simple concept, but often overlooked when comparing feed efficiency across production systems or even between groups within a production system.

Thus, dietary ingredients that lower the energy density of the diet have a direct impact on feed efficiency by increasing the pounds of feed required for each pound of gain. Because reducing the dietary energy level also can lower growth rate, low-energy diets can also indirectly increase feed-to-gain (F/G) by decreasing the denominator in the F/G equation.

Other diet variables

If the diet is deficient in any nutrient, daily gain will be reduced and feed efficiency will suffer. Of all nutrients, deficiencies in amino acids have the greatest negative impact on feed efficiency. Amino acid levels (lysine being the first limiting amino acid in most diets) should be reviewed whenever feed efficiency is not achieving target levels.

Environmental temperature

If housed below its thermo-neutral zone, the pig will use feed as a heat source to keep warm instead of using it for growth, and feed efficiency will be poorer. The economic value of these tradeoffs must always be considered.

Diet form and processing

As covered in detail by Charles Stark in this Blueprint (page 16), pigs fed pelleted diets will have 3-6% better feed efficiency than those fed diets in meal form. The quality of the pellet and the particle size of the grain in the pellet dictate much of the range of the benefit.

Reducing particle size of ingredients in the diet (whether pelleted or meal form) increases available surface area for enzymes to work on the particles, which increases digestibility, making more energy available to the pig to improve feed conversion. For each 100 micron reduction in particle size, feed efficiency is improved by approximately 1.2%.

Equipment (feed wastage)

Feed wastage can occur in many areas on the farm. Poorly adjusted feeders or old feeders that cannot be adjusted increase feed wastage and, therefore, hurt feed efficiency. (See “Feeder Adjustments Optimize Growth, Reduce Feed Wastage,” page 34).

Other efficiency robbers may not be as noticeable at first glance. For example, removing and discarding good, dry feed from feeders in the farrowing house in order to offer sows fresh feed can be a tremendous waste of expensive feed. Some automatic lactation feeding systems waste a tremendous amount of feed by dropping feed into troughs that are already full.

Likewise, over-feeding gestating sows should be quantified as feed wastage because the expense occurs without a measurable benefit. In fact, the extra feed may actually do more harm than good.

Disease

Most diseases have a much greater impact on feed intake and average daily gain than on feed efficiency. For example, gastrointestinal maladies (porcine proliferative enteritis or ileitis, haemorrhagic bowel syndrome or HBS, etc.) may affect growth rate, but have less impact on feed efficiency. This is the reason that some groups of pigs can have very low daily gain and feed intake and still have good feed efficiency numbers.

However, diseases such as porcine circovirus, with high mortality rates late in the finishing stage, are devastating to whole-herd or finishing closeout feed efficiencies. Diseases that increase mortality reduce the weight generated from the group, while feed disappearance remains high, thereby resulting in poorer feed efficiency. Feed efficiency is increased by 1.5 to 2% for each 1% increase in mortality.

Diseases such as porcine circovirus that cause a tremendous immune response also reduce the efficiency of feed use directly, in addition to their impact on mortality. Immune activation diverts nutrients away from growth towards the immune system, which results in poorer feed efficiency. For many diseases, this effect is too small to directly measure a change in feed efficiency; however, this impact is much greater and more measurable for other diseases.

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