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A Further Look at Phosphorus, Phytate, and Phytase in Monogastric Nutrition

thesis
posted on 05.01.2022, 17:12 by Olufemi BabatundeOlufemi Babatunde
The objective of this dissertation was to investigate areas that needed further research with regards to phosphorus, phytate, and phytase in monogastric nutrition. To fulfill this objective, a total of 6 studies were carried out.
Study 1 was designed to evaluate the additivity of apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of phosphorus (P) in mixed dies containing corn and soybean meal (SBM) and fed to broiler chickens. There were 7 dietary treatments in a randomized complete block design with body weight (BW) serving as the blocking factor. Treatments consisted of 4 semi-purified diets prepared to contain either corn or SBM as the sole source of P with or without phytase supplementation at 1,000 FYT/kg; 2 mixed diets containing corn and SBM with or without phytase addition; and a P-free diet (PFD) formulated to determine the basal endogenous loss (BEL) of P. A total of 512 day-old broiler chicks were fed a commercial starter diet for 21 days while experimental diets were fed for 3 days (day 22-24 post hatching). The BEL of P in broiler chickens as determined by the PFD was 166 mg/kg dry matter (DM). The SID of P in corn and SBM was 52.2 and 65.4 %, respectively. Phytase addition improved (P < 0.05) both the AID and SID of P in the ingredient and mixed diets. There was no difference between the predicted and determined AID and SID of P in the mixed diets and were thus additive. It was concluded that the AID and SID of P in corn and SBM were additive with or without phytase addition. However, we could not be certain if the assumption of additivity will hold true in mixed diets containing ingredients with a higher phytate content and if age of birds affected the BEL of P.
In the 2nd study, the additivity of AID and SID of P in mixed diets containing corn and canola meal (CCM) was investigated in broiler chickens at 2 ages. A total of 588 broiler chickens was used in this study. Dietary treatments were arranged as a 2 × 3 × 2 factorial with 2 ages (day 13 and 21), 3 diets (corn, canola meal, and CCM), and 2 levels of phytase (0 and 1,000 FYT/kg) in a randomized complete block design. A PFD was fed to birds at both ages to determine the effects of age on the BEL of P. A commercial starter diet was fed from day 1 to 10 or 18 post hatching and then experimental diets were fed for 3 days until day 13 or 21, respectively. The AID and SID of P was higher (P < 0.05) in birds at day 13 as compared with birds at day 21 regardless of phytase addition. Similarly, the BEL of P in younger birds was higher (P < 0.01) than in older birds at d 21. Regardless of age or phytase supplementation, the predicted and determined AID and SID of P in the CCM diets were similar and thus additive. In conclusion, age influenced the BEL of P and the utilization of minerals in broiler chickens while the assumption of additivity held true when mixed diets containing CCM was fed to birds at both ages with or without phytase addition.
In order to evaluate the efficacy of a new consensus phytase variant, the 3rd and 4th studies investigated the responses of broiler chickens to varying concentrations of phytate phosphorus (PP) and the new consensus bacterial 6-phytase variant (PhyG) in the starter and grower phases, respectively. Responses evaluated included growth performance, tibia ash, AID and total tract retention (TTR) of nutrients. A total of 1,152 and 768 day-old male broiler chickens were used in the starter and grower phases, respectively. Dietary treatments were arranged as a 3 × 5 + 1 factorial with a nutrient-adequate positive control (PC) (2.8 g PP/kg) and 15 nutrient-reduced negative control (NC) diets with 3 levels of phytate (NC1, NC2, and NC3 with 2.3, 2.8, and 3.3 g PP/kg respectively), and 5 levels of PhyG (0, 500, 1,000, 2,000, and 4,000 FYT/kg). Rice bran served as the main source of PP in the experimental diets. All treatments had 6 replicates with 12 birds/cage in the starter phase (day 1 to 11 post hatching) and 8 birds/cage in the grower phase (day 12 to 23 post hatching). Birds fed the PC had greater responses (P < 0.05) as compared with birds fed the NC2 diets without phytase at the starter and grower phases. There was no interaction between PP and PhyG on responses of birds in the starter phase but there was an interaction effect (P < 0.05) on the AID of some amino acids (AA) in birds at the grower phase. Increasing levels of PP reduced (P < 0.05) the growth performance, Ca and P utilization of birds but had no effect on the tibia ash in the starter phase and grower phases. Phytase supplementation improved (P < 0.05) the growth performance, AID and TTR of nutrients, and tibia ash of birds in the starter and grower phases. In conclusion, increasing PP levels reduced some responses of birds in the starter and grower phase while PhyG inclusion improved all responses of broiler chickens at both phases.
The time effects of phytase on the P utilization of growing and finishing pigs was investigated in the 5th and 6th studies, respectively using growth performance, apparent total tract digestibility (ATTD) of nutrients, P excretion, and plasma mineral concentrations as evaluation parameters. In both studies (Exp 1 and 2), treatments were arranged as a 3 × 4 factorial in a randomized complete block design with 3 corn-SBM based diets including a P-adequate PC, a low-P NC, and NC + 1,000 FYT/kg; and 4 sampling time points at days 7, 14, 21, and 28 in Exp 1 and days 14, 26, 42, and 55 in Exp 2. Ninety-six growing pigs were used in both trials with an average BW of 19.8 ± 1.16 kg in Exp 1 and 49.8 ± 3.21 kg in Exp 2. Each treatment had 8 replicates evenly divided between barrows and gilts, and 4 pigs per pen. There was an interaction (P < 0.01) between time and diet on some growth performance parameters in pigs in Exp 1 but none in Exp 2. Pigs fed the PC had greater (P < 0.05) growth performance and ATTD of nutrients as compared to pigs fed the NC in both trials. Phytase supplementation improved (P < 0.05) the ATTD of P and Ca in pigs as compared with pigs fed the NC. There was an interaction (P < 0.05) between time and diet on the total and water-soluble P lost from pigs in Exp 1. Supplementing the NC with phytase reduced the water-soluble P by 45, 32, and 35 % over the growing, finishing and the entire grow-finish period, respectively. In Exp 2, plasma concentrations of P were increased (P < 0.05) over time. In conclusion, phytase improved the responses of growing pigs however, some of these responses were influenced over time.
In summary, the AID and SID of P in corn, SBM, and canola meal are additive in complete diets with or without the inclusion of phytase. The BEL of P could be affected by the age of birds. A new consensus phytase variant seems to be efficient in improving the productivity of broiler chickens regardless of the presence of varying concentrations of PP and the growth phase of the birds. Phytase supplementation improves the P utilization and reduces the P loss of growing and finishing pigs however, this may be influenced by time within each growth phase.

History

Degree Type

Doctor of Philosophy

Department

Animal Sciences

Campus location

West Lafayette

Advisor/Supervisor/Committee Chair

Olayiwola Adeola

Additional Committee Member 2

Kolapo Ajuwon

Additional Committee Member 3

Darryl Ragland

Additional Committee Member 4

Darrin Karcher

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