EFFECTS OF PARTICLE-SIZE AND ORIGIN OF CALCIUM SOURCES ON EGGSHELL QUALITY AND BONE MINERALIZATION IN EGG-LAYING HENS

Eggshell quality and tibial ossification were studied in ISA brown egg-laying hens. Diet was supplemented with calcium sources differing in origin (seashells treated with phosphoric acid, oyster shells, and limestone) and particle size (ground or particulate). Egg production, egg mass, and feed efficiency were not affected by the origin or particle size of calcium sources. Feed consumption and live weight were higher in birds fed particulate sources, especially when ground and particulate oyster shells were compared. There was a significant interaction (source origin x particle size) in eggshell quality criteria. Egg weight was lower for hens fed ground limestone than for those fed ground seashells and particulate limestone. The latter group also had larger eggs than the group fed particulate oyster shells. Eggshell weight was higher for hens receiving particulate limestone than for those fed ground limestone and particulate oyster shells, but shell index values were similar whatever the calcium sources. Eggshell-breaking strength was higher in eggs of birds fed diets incorporating ground seashells and particulate limestone than in eggs of birds fed ground limestone. Tibial-breaking strength variables and percentage ash were greatly increased by the use of particulate calcium sources but were unaffected by the origin of calcium sources. Plasma concentration of total calcium was increased in the hens fed on the particulate seashell diet during eggshell formation. Plasma level of inorganic phosphorus was higher when the birds were given ground limestone. There was no effect of the particulate seashells and the ground limestone on metabolizable energy, nitrogen, and calcium retention.