The ability of laying hens to regulate phosphorus intake when offered two feeds containing different levels of phosphorus

The ability of laying hens to adjust their intake of available P (AP) was investigated with a maizesoyabean diet fed to forty-eight individually caged birds in a 2*4 factorial experiment. From 19 to 25 weeks of age (phase 1) twenty-four birds were fed a normal-P (NP) diet (2·2 g AP/kg DM) and twenty-four were fed a low-P (LP) diet (1·1 g AP/kg). LP eggs were lighter (51 v. 54 (SEM 1·0) g; P<0·05), providing evidence that the LP diet was deficient in AP. From 25 to 28 weeks of age six hens from each phase 1 treatment were fed either the NP or LP diet alone or a choice of the LP and NP feeds or a choice of the LP feed and a phytase-supplemented (PP) feed (LP diet with 400 microbial phytase units/kg). With a choice of the NP and LP feeds, the hens fed the LP diet in phase 1 ate a smaller proportion of the LP feed (34 (SEM 12·0) %) than the hens fed the NP diet in phase 1 (72 (SEM 12·0) %; P<0·05), showing that P deficiency influenced subsequent selection for AP, i.e. an appetite for P was demonstrated. In those birds offered the LP and PP feeds, the presence of phytase in one of the two feeds significantly alleviated the effect of P deficiency on egg and body weights. The proportion of the LP diet chosen was not significantly affected by phase 1 treatment; it was not necessary for the hens to eat more than 50 % of PP feed.