Effects of dietary calcium and phosphorus deficiency and subsequent recovery on broiler chicken growth performance and bone characteristics.

The ability of birds to modify dietary phosphorus utilisation when fed with low-phosphorus and calcium (Ca) diets was studied using different sequences of dietary phosphorus and Ca restriction (depletion) and recovery (repletion) during the grower and the finisher phases. A total of 3600 Ross 708 broilers were randomly divided into 10 replicate pens per treatment (60 per pen, six pens per block). Chicks were fed a common starter diet from days 0 to 10, then a grower control diet (C: 0.90% Ca, 0.39% non-phytate phosphorus, nPP), mid-level diet (M: 0.71% Ca, 0.35% nPP) or low Ca and nPP diet (L: 0.60% Ca, 0.30% nPP) from days 11 to 21, followed by a finisher diet C, M or L containing, respectively, 0.85%, 0.57% or 0.48% Ca and 0.35%, 0.29% or 0.24% nPP from days 22 to 37. Six treatment sequences were tested: CC, MM, LL, ML, LC and LM. Bone mineral content by dual-energy X-ray, tibia ash, toe ash weight and tibia breaking strength were measured on days 21 and 37. No significant effect was observed on growth performance throughout the experiment. Diet L reduced bone mineral content, breaking strength, tibia and toe ash by 9%, 13%, 11% and 10%, respectively, on day 21 (compared with diet C, for linear effect, P<0.05). On day 37, bone mineral content, breaking strength, tibia and toe ash remained lower compared with control values (CC v. MM v. LL, P<0.05 for linear and quadratic effects). Mineral depletion duration (ML v. LL) did not affect bone mineral status. Replenishing with the C diet during the finisher phase (LC) restored bone mineral content, tibia ash and toe ash weight better than the M diet did, but not to control levels (CC v. LC v. LM, for linear effect, P<0.05). These results confirm that dietary Ca and nPP may be reduced in the grower phase without affecting final growth performance or breaking strength as long as the finisher diet contains sufficient Ca and nPP. The practical applications of this strategy require further study in order to optimise the depletion and repletion steps.

The effects of supplementation of a novel bacterial 6-phytase on mineral digestibility and plasma minerals in lactating sows.

Pigs digest P in plant feedstuffs poorly because pigs do not produce sufficient endogenous phytase to hydrolyze P from phytate (inositol hexaphosphate). Supplementation of phytase to diets of piglets and grower-finisher pigs increased digestibility of minerals including P and Ca; however, data on phytase efficacy in lactating sows are scarce. Therefore, effects of adding a bacterial 6-phytase expressed in a strain of Aspergillus oryzae (Ronozyme HiPhos; DSM Nutritional Products, Basel, Switzerland) on apparent total tract digestibility (ATTD) of P and Ca was assessed in 45 lactating sows. Three diets were prepared: (i) positive control (PC; 0.52% available P), a regular sow diet containing inorganic P, (ii) negative control (NC; 0.20% available P) without inorganic P, and (iii) NC + 500 units of phytase/kg diet. Each diet was fed randomly to 15 sows for 21 d (from 5 d prior to farrowing to 15 d after farrowing). At day 15 after farrowing, ATTD of P did not differ between PC and NC. Phytase supplementation to NC increased (P < 0.05) ATTD of P from 34 to 46% compared to NC but did not affect (P > 0.05) ATTD of CP and Ca. On day 1 after farrowing, plasma P was 0.66 mmol/L lower (P < 0.05) in sows fed NC than PC. Phytase supplementation to NC increased (P < 0.05) plasma P by 0.40 mmol/L on day 1 but not on day 15 after farrowing. In conclusion, phytase supplementation increased P bioavailability in lactating sows.