The adaptability of Hy-Line Brown laying hens to low-phosphorus diets supplemented with phytase

Abstract

Body phosphorus homeostasis network allows laying hens to adapt to wide range of changes in dietary phosphorus levels. Phytase hydrolyzes phytate rendering phosphorus and reduces the laying hens' requirements for inorganic phosphate rock. Here, we demonstrate that there is no need to keep large safety margins in dietary phosphorus when hens are fed with phytase. Hy-Line Brown laying hens (n = 504) were randomly assigned to 7 treatments (6 replicates of 12 birds). A corn-soybean meal–based diet, with no inorganic phosphate rock, was formulated to contain 0.12% nonphytate phosphorus ( nPP ), 3.8% calcium, and 2,000 FTU/kg phytase. Inorganic phosphate rock (di-calcium phosphate) was supplemented into the basal diet to create 6 other diets containing 0.17, 0.22, 0.27, 0.32, 0.37, and 0.42% nPP. Levels of calcium carbonate and zeolite powder were adjusted to make sure all the 7 experimental diets contained the same nutrition levels (including calcium and phytase) except nPP. The diets were subjected to laying hens from 29 to 40 wk of age. As a result, when supplemented with 2,000 FTU/kg phytase, extra supplementation of inorganic phosphate rock had no effects ( P > 0.05) on serum phosphorus levels, serum calcium levels, laying performance (laying rate, egg weight, feed intake, feed-to-egg ratio, and unqualified egg rate), egg quality (shell thickness, shell strength, albumen height, yolk color, and Haugh unit), and tibia quality parameters (breaking strength and ash, calcium, and phosphorus contents). Extra supplementation of inorganic phosphate rock linearly increased ( P < 0.01) fecal phosphorus excretion and linearly decreased ( P = 0.032) the apparent metabolizability of dietary phosphorus. While serum hormones and intestine gene expressions were varied within treatments, no consistent changes were found. In conclusion, the supplementation of inorganic phosphate rock (provided 0.05–0.30% extra nPP) to phytase-containing basal diets (2,000 FTU/kg; nPP = 0.12%) provided limited benefits to egg production performance in laying hens from 29 to 40 wk of age. Further investigating the body phosphorus homeostasis would help to understand the nutritional and physiological reasonability of formulating low-phosphorus diets in the laying hen industry.

Effect of Dietary Mineral Content and Phytase Dose on Nutrient Utilization, Performance, Egg Traits and Bone Mineralization in Laying Hens from 22 to 31 Weeks of Age

“…For instance, some studies have observed an increase in P digestibility in hens fed with P-deficient diets, both at fecal and ileal level [ 27 ], reducing P excreta [ 28 ]. In fact, Ren et al [ 29 ] reported that when dietary inorganic P was overdosed, it was mainly excreted by the laying hens. Regarding Ca, although some studies observed a decrease in Ca digestibility when dietary inorganic P was overdosed [ 29 ], others have observed the opposite behavior, decreasing Ca digestibility in Ca-deficient diets [ 27 , 30 ].…”

“…In fact, Ren et al [ 29 ] reported that when dietary inorganic P was overdosed, it was mainly excreted by the laying hens. Regarding Ca, although some studies observed a decrease in Ca digestibility when dietary inorganic P was overdosed [ 29 ], others have observed the opposite behavior, decreasing Ca digestibility in Ca-deficient diets [ 27 , 30 ].…”

“…Previous works, where dietary Ca and P levels were similar to those evaluated in this research, showed contradictory results. Some studies observed that an increase in the dietary level of Ca and P did not lead to relevant modifications of these minerals in the blood [ 29 , 32 , 33 ]. However, Sari et al [ 27 ] reported that a decrease in the P level of the diet led to a clear decrease in the blood P level of the hens (8.01 vs. 4.10 mg/dL), but without modifying the serum Ca level.…”

“…In fact, Viveros et al [ 34 ] described a linear correlation between dietary non-phytate P and plasma P for different poultry species. Ren et al [ 29 ] associated these differences with the blood sample-collecting time used in the different trials.…”

“…However, most of the works reviewed in the literature show that the main determinant of the quality of the shell is the level of Ca and not so much the level of P. Bar et al [ 55 ] already observed that an increase in the Ca level produced a clear improvement in the shell weight, while the modifications of the P level had no effect. In fact, most of the studies that evaluated the effect of the inorganic P level, at a constant Ca level, did not observe any significant effect on the eggshell characteristics [ 29 , 32 , 36 , 56 ]. These results could explain why the PC diet allowed obtaining eggs with a greater shell thickness compared to NC diet, by providing a higher level of Ca, while the greater availability of P due to the inclusion of phytase did not lead to improvements in the shell quality.…”