Effects of phytase in laying hen diets reduced in available phosphorus and calcium on productivity, eggshell quality, and bone mineralization of white egg layers

• Author / Creator

  Pongmanee, Koonphol

• Phosphorus and Ca are essential for maintaining egg production and bone health of laying hens. The effects of marginal or moderate reductions in available P (aP) and Ca in layer diets, with or without phytase supplementation on performance, egg production, apparent ileal digestibility (AID) and retention of P and Ca, and eggshell and bone quality of pullets and laying hens were investigated. In Trial 1, 84 hens were fed one of seven dietary treatments. Treatments were: a positive control (PC) diet with 0.45% aP, 3.70% Ca and 0.16% Na from 25 to 28 wk, and 0.38% aP, 3.73% Ca and 0.15% Na from 29 to 37 wk; a negative control (NC) diet similar to the PC diet, but with 0.22% aP, 3.00% Ca and 0.13% Na from 25 to 28 wk, and 0.19% aP, 3.02% Ca and 0.13% Na from 29 to 37 wk; the NC diets supplemented with phytase at 150 (NC + 150), 300 (NC + 300), 600 (NC + 600), or 1,200 (NC + 1,200) phytase unit (FTU)/kg, respectively; and the PC diet supplemented with phytase at 1,200 (PC + 1,200) FTU/kg. Egg production, eggshell quality, bone traits, and AID of P and Ca were measured. The reduced aP and Ca in the NC diet did not decrease egg production, but the NC hens had lower cortical (P < 0.001) and trabecular + medullary bone mineral density (BMD; P = 0.004), and total bone mineral content (BMC; P < 0.001) than the PC hens. The NC + 600 and NC + 1,200 increased AID of P (P = 0.024). In Trial 2, one-d-old White Leghorn pullets (n = 480) were randomly allocated to six dietary treatments: a PC diet with a sequence of 0.48-0.45-0.37-0.45% aP, 1.05-1.00-0.90-2.00% Ca, and 0.18-0.17-0.16-0.16% Na for Starter-Grower-Developer-Pre-lay phases, respectively; a NC diet with marginal reduction, similar to the PC but reduced in aP, Ca, and Na by 0.15%, 0.16%, and 0.035% of the diet in each phase, respectively; the NC diet supplemented with phytase at 300 (NC + 300), 600 (NC + 600), 1,200 (NC + 1,200) or 2,400 (NC + 2,400) FTU/kg. Pullet performance, bone characteristics, and retention of P and Ca were determined. Reduced dietary aP, Ca, and Na did not decrease pullet performance, but decreased bone breaking strength at 6 wk. The NC + 2,400 birds had greater P retention than the NC + 600 and PC birds at 6 wk. In Trial 3, hens (n = 256) were maintained on the first five respective dietary treatments previously fed from hatch to 19 wk in Trial 2. Hen productivity, retention of P and Ca, eggshell quality, and bone mineralization were determined. Hen BW in the NC was lower than the PC (P < 0.001), but the NC + 1,200 restored BW. At 74 wk of age, the NC + 600 hens had higher (P < 0.001) P retention than NC + 300 hens. The NC + 600 hens had greater distal femur ash than the NC hens (P = 0.013). The NC + 600 and NC + 1,200 hens had increased total BMD of the proximal (P = 0.001) and distal (P = 0.002) femurs relative to the NC hens. Laying hens fed the NC + 600 diet had increased proximal (P = 0.002) and mid-bone (P = 0.008) total femur BMC relative to the NC hens. Hens at 74 wk had greater total BMD and BMC than at 42 wk, likely due to an increase of medullary bone. Overall, moderate (Trial 1) and marginal (Trials 2 and 3) reductions in dietary aP and Ca did not decrease hen performance, egg production, nor eggshell quality. The NC hens were able to compensate for the reductions in dietary aP and Ca by increasing the absorption of these minerals in the short- and long-term. However, the marginal reduction of dietary aP and Ca in the long-term caused a subtle decrease in hen BW. Marginally and moderately reduced aP and Ca in the NC diets decreased bone quality, and phytase supplementation at 600 and 1,200 FTU/kg restored bone quality in laying hens fed reduced dietary aP and Ca.

• Subjects / Keywords

  • Phytase
  • Phosphorus
  • Eggshell quality
  • Bone mineralization
  • Laying hens

• Graduation date

  Spring 2021

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-hps4-fa06

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.