Effects of Pellet Processing Parameters on Pellet Quality and Nursery Pig Growth Performance

Abstract. During the pelleting process, conditioning temperature can influence nutrient availability and pellet durability index (PDI). However, the impact of conditioning temperature on nursery pig growth performance is variable. Therefore, the objectives of two experiments were to: (1) compare moisture percentage among three pellet mill series, and (2) quantify growth performance differences in nursery pigs due to diet form (mash vs. pelleted), conditioning temperature (low, medium, and high), and pellet diameter (4.0 mm and 5.2 mm). Experiment 1 was a 3 × 4 factorial design with three pellet mill series of decreasing capacity (medium, small, and experimental-scale; California Pellet Mill Co., Crawfordsville, Indiana, for a medium, small, and experimental pellet mill, respectively) that produced samples collected at four locations (initial, post-conditioner, post-die, and post-cooling). Three runs were completed on each pellet mill, with the shutdown of the pellet mill indicating the end of a run. Three samples were collected from each location per run, for a total of 36 samples. Experiment 2 used 350 nursery pigs (DNA 200 × 400; initially 7.6 kg) in a 28 d experiment fed two phases, with a phase change at day 14. Seven treatments were arranged in a 2 × 3 factorial design plus an unpelleted mash control, with the factors of pellet diameter (4.0 mm and 5.2 mm) and conditioning temperature (low, medium, and high). Data were analyzed using the GLIMMIX procedure of SAS (version 9.4). In experiment 1, there was a significant pellet mill × location interaction (p = 0.012) for moisture percentage. Because moisture is added via steam at the conditioner, only the conditioning location results are described. Regardless of pellet mill type, moisture was highest in conditioned samples. However, conditioned samples from the experimental-sized pellet mill had over 1% greater (p < 0.05) moisture than samples from the medium and small pellet mills. This increase in moisture is one reason why higher (p < 0.05) PDI values were found in pellets from the experimental pellet mill compared to the medium and small pellet mills. In experiment 2, increasing conditioning temperature improved (p < 0.0001) PDI. The interaction of pellet diameter × conditioning temperature did not impact (p > 0.10) overall nursery pig feed efficiency (G:F). However, for overall G:F, both main effects tended to be significant (p < 0.10), which was caused by pigs having greater (p < 0.05) G:F when fed larger-diameter pellets conditioned at a low temperature, compared to pigs fed smaller-diameter pellets conditioned at a high temperature. Regardless of parameter, pigs fed pelleted diets had 4.5% greater (p < 0.05) G:F than those fed mash diets. In summary, pellet mill size is important to consider when evaluating factors that impact pellet quality, such as percentage moisture. Increasing conditioning temperature is one method to improve PDI, but there was a tendency to reduce nursery pig G:F when feeding two phases of diets in a 28 d study. In conclusion, conditioning feed at lower temperatures may improve nursery pig G:F when starting pigs on a new diet. Keywords: Moisture, Pelleting, Starch.