The effect of the extrusion process on the digestibility of feed given to laying hens

The purpose of the study was to observe the effect of feeding extruded feed that contained rapeseed (that was extruded using the standard methods for large-scale production of extruded feed) on retention and coefficient of total tract apparent digestibility (CTTAD) in hens. The laying hens were divided into two groups NEX and EXT. The composition of the diets was the same in both groups (wheat 39%, rapeseed 13.5%, pea 13.5%, soya bean meal 6%, maize 14%, fish meal 3%, limestone 1%, premix 10%). But 0.45 kg of 1 kg of the diets EXT (wheat, pea, and rapeseed) was extruded by dry extrusion at temperature 137 °C and at moisture from 12 to 18% for 16 s. A balance assay was conducted with four laying hens from group NEX and eight from group EXT when they were 61 weeks old. The CTTAD of fat, calcium and amino-acids, and the retention of the nitrogen were estimated using the indicator method. The significance between the means was evaluated by a t-test. The average egg mass production during the assay was for group NEX 45 ± 3.9 g/hen/day and for group EXT 50 ± 5.0 g/hen/day. The extrusion process significantly increased (P < 0.001) the CTTAD of fat from 0.807 (NEX) to 0.937 (EXT). The coefficient of nitrogen retention was higher in group EXT (0.629) than in group NEX (0.584). The extrusion significantly increased the CTTAD of arginine (P < 0.05, NEX: 0.929, EXT: 0.944) and isoleucine (P < 0.05, NEX: 0.870, EXT: 0.904). The extrusion had a tendency to increase the CTTAD of leucine (P < 0.1, NEX: 0.885, EXT: 0.907), glutamic acid (P < 0.1, NEX: 0.931, EXT: 0.945), glycine (P < 0.06, NEX: 0.823, EXT: 0.859) and alanine (P < 0.1, NEX: 0.806, EXT: 0.844). CTTAD of lysine was almost the same in both groups (NEX: 0.950 and EXT: 0.949). The extrusion process had a tendency to decrease the CTTAD of histidine (P < 0.06, NEX: 0.906, EXT: 0.859) and tyrosine (P < 0.07, NEX: 0.974, EXT: 0.921). The extrusion had a positive effect on the fat CTTAD, nitrogen retention and on the CTTAD of the essential amino-acids (except lysine and histidine). The decrease in the digestibility of these two amino-acids was not significant.