[Some causes of laying performance decrease in chickens and possibilities of its improvement]

alkaline phosphatase blood calcio calcium deficiencia de minerales deficiencia de vitaminas egg characters eggs fosfatasa alcalina fosforo gallina ponedora huevos layer chickens laying performance mineral deficiencies minerales minerals oeuf performance de ponte ph phosphatase alcaline phosphore phosphorus poule pondeuse rendimiento en la postura sang sangre tocoferoles tocopherol tocopherols vitamin d vitamin deficiencies vitamina d vitamine d