Effects of dietary humic substances on egg production and egg shell quality of hens after peak laying period

Ninety Isa Brown layers from 51 to 61 weeks of age were allocated to three treatment groups, namely H-0, H-1 and H-2. Control (H-0) hens were fed a commercial diet while H-1 and H-2 hens were fed a diet including 30 and 90 ppm dietary humic acid in liquid form, respectively. Hens were placed individually in cages in three tier batteries. Egg production (% hen-day) in the H-2 group was higher (P < 0.05) than control group. Egg mass of H-2 hens was higher (P < 0.05) than H-0 and H-1 hens. Total feed intake in H-2 group was significantly higher (P < 0.05) than H-1 group. Egg shell thickness of H-1 hens was higher (P < 0.05) than H-2 hens. Egg shell strength of H-1 hens was higher (P < 0.05) than control and H-2 hens. Egg weight, feed conversation ratio and yolk weight were not affected by dietary humic substances. These results indicated that the supplementation of 30 ppm humic acid into the diet may increase the egg shell strength without affecting egg production and feed efficiency compared to control counterparts.