Expansion and pelleting of starter, grower and finisher diets for pigs: effects on nitrogen retention, ileal and total tract digestibility of protein, phosphorus and calcium and in vitro protein quality

The nutritional effects of feed expansion and pelleting were evaluated in digestibility experiments involving 40 castrates (Belgian Landrace×Piétrain) which were kept from 20 to 100 kg of body weight. The animals were successively fed a starter, grower and finisher diet containing barley, wheat, soyabean meal and cassava. The diets were subjected to either expansion at ∼100°C, or pelleting at ∼80°C, or expansion followed by pelleting. The unprocessed control diet was fed as meal. The pigs were divided into four groups and fed one of the experimental diets. With each pig, two 5-day digestibility trials were performed with the starter, grower and finisher diet, respectively. Neither feed intake, weight gain or feed:gain ratio of starting, growing and finishing pigs was significantly (P>0.05) affected by one of the applied feed processing methods. Expansion of the meal diets had no significant effects on protein utilisation as measured by N-retention and apparent ileal and total tract N-digestibility. Feeding of the pelleted grower and finisher diets (without or with preceding expansion) significantly (P<0.05) increased apparent total tract protein digestibility, while ileal protein digestibility, nitrogen retention, and ileal and total tract dry matter digestibility were also improved, but not always significantly at P=0.05. In vitro tests showed that feed processing led to significantly (P<0.05) higher available lysine and had no effect on amounts of free amino acids. Feed expansion tended to decrease protein solubility at alkaline pH, but pelleting caused a significant (P<0.05) increase, which appeared to be paralleled by higher protein digestibility in the growing and finishing pigs. Ileal and total tract digestibility of phosphorus and calcium were impaired when pigs were fed the expanded or pelleted diets. When expansion was followed by pelleting, the negative effects on phosphorus and calcium digestibility were reduced.