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 to 83 wk). Each treatment consisted of 42 hens (7 hens x 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 were found in the C system with 50FL: 50CL and 0FL: 100CL and in the S system with 30FL: 70CL between 76 and 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 and 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 d in a split feeding system to improve shell quality in old, brown laying hens in an extended production cycle.