Abstract
Chickens adapt to P and Ca restriction during the very first days of life by improving P utilisation efficiency. The present study was built to identify the mechanisms underlying this adaptive capacity, and to identify the optimal window of application of the restriction (depletion). A total of 1600 Cobb 500TM male broilers were used. During each phase (from age 0 to 4 d, 5 to 8 d, 9 to 18 d and 19 to 33 d), the animals received either a control diet (H) or a restricted diet (L) with reduced levels of non-phytate P (nPP) and Ca (between -14 and -25 % for both) with four dietary sequences: HHHH, HLHL, LHHL and LLHL. None of the feeding strategies affected growth. Tibia ash content at day 4 and 8 was impaired when the L diet was fed from 0 to 4 and 5 to 8 d, respectively (P = 0⋅038 and P = 0⋅005). Whatever the early restriction period or length between 0 and 8 d of age, the mineralisation delay was compensated by day 18. This was accompanied by an increased mRNA expression of the Ca transporter, CALB1, and an increased apparent ileal digestibility of Ca at day 8 (P < 0⋅001). This adaptation was limited to the starter phase in restricted birds. No effect was seen on P transporters mRNA or protein expression. In conclusion, birds adapted to mineral restriction by increasing Ca and nPP utilisation efficiencies. Depletion-repletion strategies are promising in improving the sustainability of broiler production but need to be validated in phytase-supplemented diets.
Highlights
Chickens adapt to P and Ca restriction during the very first days of life by improving P utilisation efficiency
Digestibility of phosphorus and calcium and mRNA and protein expression of their transporters At day 8, the apparent ileal digestibility (AID) of P and Ca as well as disappearance of phytate P (PPdisp) were higher for birds receiving the L diet between 5 and 8 d of age (HL and LL compared with HH and LH, P ≤ 0⋅001, P ≤ 0⋅001 and P = 0⋅002, respectively; Table 5)
There was a higher mRNA expression of CALB1 in birds with the LL diet compared with birds receiving HH or LH diets (P ≤ 0⋅001)
Summary
Chickens adapt to P and Ca restriction during the very first days of life by improving P utilisation efficiency. A recent study (MM Van Krimpen, E Willems and HJ Van Harn, unpublished results) failed to observe such a long-term adaptation in birds fed a deficient Ca and nPP diet from 0 to 4 d of age, which showed decreased P and Ca pre-caecal digestibility at day 37, without any variation in the mRNA expression of CALB1, ATP2B1 and SLC34A2. These conflicting results suggest a lack of knowledge about the degree of dietary nPP and Ca reduction, the timing and/or the duration of the depletion required to induce a long-term adaptation in the birds
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