Good quality piglet feeds are habitually rich in protein, lactose and occasionally table sugar (sucrose) and dextrose. Lysine from protein or as added in crystalline form and reducing sugars (such as those described above), can combine under the right conditions of heat and humidity and form indigestible compounds. Thus, most piglet feeds contain higher dosages of this lysine to safeguard against projected losses because of pelleting and storage.
Simplified Maillard reaction
In general, when amino acids are heated under humidity a chemical reaction called "the Maillard reaction" takes place. This involves the binding of free amino groups (such as those in crystalline lysine, which in contrast to other amino acids lysine contains two such groups) to reducing sugars (as those from lactose and sucrose/dextrose). This "browning" reaction occurs even at normal room temperatures, but at a very slow rate. However, when browning is excessive (during improper pelleting conditions, for example) or it is out of control (during prolonged storage at high temperatures and humidity), then protein quality is invariably reduced.
A prolonged storage of heat sensitive material that have already been affected by this problem, initiates a second cycle of Maillard reaction. This is of paramount importance in nursery feed management, because the conditions in commercial nursery facilities are extremely favorable for the Maillard reaction. Residual feed moisture also affects the extent of the Maillard reaction during storage. For example, a 10 percent moisture level in milk powder stored for 10 weeks during summer resulted in 20 percent loss of lysine bioavailability. Or, as it was demonstrated in another study, 10 percent of total lysine was destroyed when piglet feed was stored inside a typical nursery room for only 7 days!
In addition, the adverse effects of the Maillard reaction have been demonstrated in many other feed ingredients such as soybean meal, fish meal, dried whey, canola meal and peanut meal. Although crystalline lysine is the most sensitive amino acid, the same problem exists (but to a lesser degree) for the rest of the crystalline amino acids added in piglet feeds. So, this is a serious problem affecting many ingredients when heated under humid conditions.
Fresh piglet feed
Manufacturing piglet feeds at farm level is the most secure way to ensure fresh feed is always used before quality starts to deteriorate. Home mixing also ensures that small quantities are possible instead of ordering a full truckload that may require a month to be consumed.
For those farms unable to prepare piglet feed on-site, buying feed from a reputable feed supplier with a record of quality is a sound practice to ensure fresh feed. Still, laboratory checks should be performed periodically to test for "reactive lysine," and one of the tests should measure the damage due to the Maillard reaction. One simple solution is to avoid pelleted feed and opt for coarsely ground feed that has not undergone any heat treatment. Thus, one cycle of Maillard reaction can be avoided altogether.
Nevertheless, once the piglet feed arrives at the farm, all bags should be stored in a cool area to preserve nutrients and flavors. As a rule, feed bags should never be stored inside the nursery room as this ensures the feed remains not only fresh, but also that it retains its original aroma. Finally, young pigs should never be given more than a days' supply of feed at any time. The piglets should instead be fed on a little-but-often basis.