Effect of feed restriction on digestibility, digestive enzymes and economic traits of silkworm

Effect of feed restriction on important economic traits, digestive enzymes and digestibility of mulberry leaves was studied in the 1650 forth instar of silkworm larvae. After mass-reared of first three larval instars, 15 trays of 4th instar of silkworms were reared separately including four treatment plus control (T1). Dietary restriction treatments were one-third (T2) and two-third(T3) of feed requirements starting from fourth and one-third (T3) and two-third(T4) starting from fifth larval instar. Digestibility of mulberry leaves was measured in each instar separately. Protease, lipase and α-amylase activities were determined on 4th day of 5th instar in 10 silkworm larvae. The results showed the activity of enzymes protease, lipase and amylase in T2 were 16.49, 47.8 and 211.7 and in T3: 15.76, 47.1 and 408.3, which were all more than T1: 8.16, 23 and 10 μM/min/mg respectively (P<0.05). The activity of enzymes protease and lipase in T4 were 16.77 and 55.1 and in T5: 14.37 and 65.5 μM/min/mg that was more than control (P<0.05). Digestibility of dry matter intake in T2 and T4 were 48.26 and 41.29%, which were more than T1: 39.85% significantly (P<0.05). Due to food restriction treatments the weight of wet cocoons and the weight of pupae decreased but cocoon shell weight did not change significantly (P<0.05). These results indicated that whenever the mulberry leaves feeding is restricted; while the larval duration increases, the activity of digestive enzymes could increase to digest most of feed effectively and produce the required silk protein for cocooning.