Supplementation of fine and coarse limestone in different ratios in a split feeding system: effects on performance, egg quality and bone strength in old laying hens

Different ratios of fine- (FL) and coarse limestone (CL) were compared (50FL:50CL, 30FL:70CL, 0FL:100CL) in conventional (C) and split feeding (S) for their effects on performance, egg quality traits and bone quality of old brown laying hens (72-83 wk). Each treatment consisted of 42 hens (7 hens × 6 replicates). In the C system diets supplemented with limestone were provided during the whole day, whereas in the S system a morning diet was fed without added limestone and only the afternoon diet was supplemented with different limestone ratios. Highest laying %, egg mass and lowest feed conversion was found in the C system with 50FL:50CL and 0FL:100CL and in the S system with 30FL:70CL between 76-79 wk (P ≤ 0.001). Reduced cracked egg % was found when 0FL:100CL was supplemented in the C system and 30FL:70CL in the S system between 72-83 wk (P ≤ 0.001). Tibia ash content was higher in the S system compared to the C system (P = 0.005), tibia breaking strength however, did not differ between feeding systems. Egg quality traits were not improved by S feeding. However, at 83 wk S feeding resulted in higher breaking strength, but lower shell thickness compared to the C system (P = 0.036, P ≤ 0.001, respectively). Therefore, hens in the S feeding system might have been able to form a structurally superior shell compared to the C system. For further investigation, instead of restricting limestone supplementation solely to the afternoon, it might be a better approach to provide FL and CL at a different time of the day in split feeding system to improve shell quality in old brown laying hens in an extended production cycle.