Effects of pelleting and storage of a complex nursery pig diet on lysine bioavailability

The effects of pelleting and storage of a complex nursery pig diet (28% lactose and 1.4% lysine) on lysine bioavailability were assessed in a chick bioassay. The nursery diet was steam-conditioned at 60 degrees C for 45 s and then pelleted through a 5-mm die with a depth of 38 mm. Samples of meal and pelleted diet were placed in metallic feeders in an occupied nursery facility for 1 wk (warm) or were stored at 4 degrees C (cool). For the standard-curve bioassay, a total of 144 8-d-old chicks were offered the following dietary treatments: 1 to 3) a basal diet (lysine deficient) and two levels (.08 and .16%) of added lysine (from L-lysine-HCl); 4 and 5) two positive controls (.7% added lysine with or without 10% of the nursery diet); and 6 to 9) basal diet plus 10% of one of the four nursery diet samples (meal or pellet stored cool or warm for 1 wk). Pelleting had no effect (P>.10) on lysine bioavailability, probably because pelleting conditions (temperature, humidity, and pellet size) were not aggressive enough to result in detectable effects on lysine utilization. However, storage in the nursery facility for 1 wk reduced (P<.03) lysine bioavailability by an average of 10%. No significant (P>.10) interactions were observed. Furthermore, true digestibility of lysine in the four pig diet samples was estimated in a cecectomized cockerel digestibility assay using 15 adult Single-Comb White Leghorn cockerels. Lysine digestibility in all samples was high (average of 94%) and was not affected (P>.10) by treatment. We conclude that the pelleting conditions used in our experiments did not decrease lysine utilization. More research is needed to define thermal processing conditions that might cause protein quality deterioration. However, typical warm and humid environmental conditions encountered in modern nursery facilities have a negative effect on protein quality of diets rich in reducing sugars and lysine.