Protein utilisation, lysine bioavailability and nutrient digestibility of shrimp meal in growing pigs

Protein utilisation, lysine bioavailability and total tract apparent digestibility of shrimp meal (SM) were investigated using 12 crossbred castrated male pigs with an average initial body weight of 35 kg. The experimental set-up was an incomplete block design with four diets and two periods of 14 days each. In each period, 7 days were for adaptation to diets and 7 days for collection of faeces and urine. A basal diet, formulated to provide 5.5 g lysine/day, was supplemented with either casein (reference) or coarse or fine SM to supply additional lysine at 4.5 (casein) and 3.2 (SM) g/day, respectively. The SM contained (g/kg dry matter (DM)) crude protein, 215; ash, 560; acid detergent fibre (ADF), 234; neutral detergent fibre (NDF), 284; chitin, 155; lysine, 8 and methionine, 3.6. Faecal and urinary N excretion were increased in SM diets compared to the casein diet (P<0.001), and the increment was greater for faecal than for urinary N excretion. Nitrogen retention in SM diets was 27% lower (P<0.0001) than in the casein diet, resulting in a relative decrease in net protein utilisation and the biological value of 58 and 24%, respectively. Bioavailability of lysine determined by the slope ratio assay, in coarse and fine SM was 0.66 and 0.62, respectively, when using N retention as the response criterion and assuming a bioavailability of lysine from casein of 100%. A reduction in particle size of SM did not affect N utilisation or lysine bioavailability. Fine grinding decreased the total tract apparent digestibility of ADF and chitin, and tended to decrease DM, N, ash and NDF digestibilities. Digestibility coefficients of coarse SM for DM, N, organic matter, ADF, NDF, NDF (ash-free) and chitin were 0.31, 0.53, 0.41, 0.47, 0.60, 0.73 and 0.66, respectively. Digestible and metabolisable energy concentrations in coarse SM were 3.35 and 2.98 MJ/kg DM (7.16 and 6.37 MJ/kg organic matter), respectively. Results indicate that the protein value of SM when having high fibre, high ash and low protein concentrations is only moderate. Intensive grinding was not a successful method to improve nutrient digestibility and energy value of SM.