Effects of dietary phosphorus and calcium levels and phytase supplementation on bone metabolism of egg-laying hens

• Author / Creator

  Abiodun Bello

• The importance of this Ph.D. thesis work is to assess the effects of dietary available phosphorus (avP) and calcium (Ca) levels and phytase supplementation in egg-laying hens and broilers. Two trials were conducted to evaluate the effects of marginal, moderate, and severe reduction in dietary avP and Ca levels with or without phytase supplementation on performance, eggshell quality, and bone metabolism of egg-laying hens and one trial was conducted to study the phytate-degrading efficacy of two phytases at two doses in broilers. In trial 1, 456 laying hens (4 per cage) were fed one of three diets from 30 to 70 weeks of age (woa). The diets were (1) a positive control (PC), based on primary breeder recommendation for nutrient specification, (2) a negative control (NC; the PC with avP and Ca levels marginally reduced by 0.146 and 0.134% of the diet, respectively); and (3) the NC supplemented with 300 FTU/kg phytase (NC+PHY). Egg production, BW, feed intake, FCR, and eggshell quality from 30 to 70 woa, and apparent ileal digestibility of P and Ca, and the majority of bone quality measured were not affected by diet. In trial 2, 100 hens were fed one of five diets from 68 to 78 woa. The diets were (1) a PC with 0.35% avP and 3.5% Ca, (2) a NC1, the PC moderately reduced in avP and Ca by 0.187 and 0.159% of the diet, respectively, and (3) a NC2 which had the PC severely reduced in avP and Ca by 0.231 and 0.275% of the diet, respectively. Other diets for the trial 2 were the NC1 and NC2 supplemented with 600 FTU/kg phytase (4) NC1+PHY and (5) NC2+PHY. Egg production and FCR were maintained by the NC1 but were 11.9% lower and 12.3% higher, respectively, by the NC2 than the PC, which was alleviated by the supplemental phytase. Diet effects on feed intake and eggshell quality traits followed a similar pattern. Body weight was 2.9% lower for NC1, and 6.1% for NC2 than the PC and the phytase use in the two diets alleviated the decreased BW. Cortical bone mineral density was 1.6% higher in PC hens than in NC2 hens, and 3D medullary bone volume to non-bone and bone mineral density tended to be lower (P<0.068) in the NC2 hens than in hens fed other diets. The marginal reduction in avP and Ca levels in the NC diet in trial 1 maintained performance, eggshell quality, and bone traits, indicating that the mineral levels in the diet were not deficient, and therefore the efficacy of phytase to alleviate the adverse effect of the deficiency could not be evaluated. The moderate reduction of avP and Ca levels in the NC1 of trial 2 maintained performance with decreased BW and bone quality, which were alleviated by phytase addition in the diet to determine efficacy of phytase in mineral-reduced diet on bone metabolism. The severe reduction of avP and Ca levels in the NC2 decreased performance, eggshell quality and bone properties, and phytase supplementation alleviated the adverse effects all parameters with only partial alleviation on the densitometry and micro-architectural bone traits. For the phytate-degradation trial, 1,890 broilers were fed one of seven diets. The diets included a (1) PC; the PC reduced in avP and Ca by 0.146 and 0.134% of the diet respectively (2; NC1) or by 0.174 and 0.159% of the diet, respectively (3; NC2), and (4 and 5) NC1 + PHYA or PHYB at 500 FTU/kg and (6 and 7) NC2 + PHY A or PHYB at 1,000 FTU/kg. Result of the study validated that the efficacy of phytases to dephosphorylate phytate and increase P and Ca availability differ and that the higher dose was more effective than the lower dose. Overall, high and deficient dietary avP and Ca levels lowered quality of bone tissues; however, phytase supplementation in avP- and Ca-deficient diet degrades phytate to increase the minerals availabilities in a dose- and phytase type-dependent manner and subsequently maintain fortified bone in poultry.

• Subjects / Keywords

  • Calcium
  • Inositol phoshates
  • Phytase
  • Phosphorus
  • Laying hen
  • Bone

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R33X84253

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.