Influence of aluminum on phosphorus availability in laying hen diets

An experiment was conducted to determine the influence of Al on P utilization, as well as to determine the short-term response of laying hens to diets containing different levels of P not bound by A1 (PNB). One hundred and sixty Single Comb White Leghorn hens were assigned to eight treatment diets derived from a 2 by 4 factorial design. Diets varying in two percentages of total P (.5 and 1.0%) and four percentages of Al supplementation (.6, .4, .2, and 0%) from aluminum acetate were fed for 15 days. The calculated PNB for the eight treatments were .03, .18, .33, .48, .53, .68, .83, and .98%, respectively. Egg production and feed intake were significantly lower at the two lowest percentages of PNB (.03 and .18%). At the lowest PNB level (.03%), no eggs were laid during the last 2 days of the experiment by any of the 20 hens fed this diet. Plasma inorganic P was significantly decreased by either lowering the total P of the diet or by increasing the Al. These detrimental effects of Al supplementation were completely reversed by increasing the level of P in the diet. Therefore, the detrimental effects of Al are not due to Al per se, but rather are due indirectly through diminishing P availability. Decreased egg specific gravity caused by high percentages of P was reversed by Al supplementation. As the amount of PNB increased, feed consumption also increased. Maximum feed efficiency and egg production were achieved with PNB values between .33 and .98%.