Menu
Adequate dietary Ca and available phosphorus (avP) levels are essential to maximize long-term egg production and bone health in laying hens. Approximately 60% of P in plant-based feed ingredients is poorly digestible in the gastrointestinal tract of chickens. The low availability of P in plant-based feed ingredients increases the need for dietary inorganic P supplementation. However, increased dietary supplementation of inorganic P also increases feed cost, which drives the use of phytase in poultry diets. The objectives of the current study were to assess the long-term effects of dietary Buttiauxella sp. phytase (BSP) on egg production, BW, feed intake, FCR, shell quality, bone density, and apparent ileal digestibility of P (AIDP) and Ca (AIDCa) in Lohmann LSL Lite layers from 30 to 70 woa.
Lohmann LSL Lite white laying hens (n = 456, 27 woa) were randomly housed with 4 hens in each of 114 cages. All the hens were fed a nutrient-adequate diet from 27 to 30 woa for adaptation to the cages. At 30 woa, 3 experimental diets were each assigned to 38 cages and fed in 2 dietary phases: phase I from 30 to 48 woa and phase II from 49 to 70 woa. The diets were a positive control (PC), formulated based on the primary breeder recommendations; the PC diet with avP and Ca marginally reduced by 0.146 and 0.134% of the diet, respectively (negative control; NC); and the NC diet supplemented with BSP at 300 FTU/kg (NC+BSP). Hen-day egg production data, individual hen BW and average daily feed intake were collected on a 4-wk basis. At 30, 38, 46, 54, 62, and 70 woa, eggs produced within 24 h were collected from 8 randomly pre-specified cages per treatment for determination of specific gravity and eggshell breaking strength (kgF), thickness (mm), and relative shell weight (%). At the start of the experiment, hens in 2 pre-identified cages per treatment (4 hens × 2 cages × 3 diets) were selected at random. At 30, 38, 46, 54, 62, and 70 woa, each of the hens was anesthetized and analyzed in vivo for tarsometatarsus bone densitometry analysis. Also at 32, 48, and 70 woa, hens in 2 pre-identified cages per treatment (2 hens × 8 cages × 3 diets) were euthanized, and the right femurs were removed and subsequently analyzed ex vivo for bone densitometry, breaking strength (BBS), and ash content.
There was no diet × age interaction for BW. However, BW tended to be higher (P = 0.076) in the PC and NC+BSP hens than in NC hens from 34 to 70 woa. Egg production, feed intake, FCR, egg specific gravity, and eggshell breaking strength, thickness, and relative weight were not affected by diet × age interaction or diet main effect. Egg specific gravity, shell thickness, and relative shell weight decreased with increasing hen age (P < 0.001). In vivo tarsometatarsus densitometry was not affected by the diet × age interaction. Tarsometatarsus total BMD was lower (P = 0.046) in both PC and NC+BSP hens than in the NC hens, with no diet effect on any other bone densitometry parameter. Ex vivo total BMD in the femur proximal metaphysis was higher in the NC hens than in both the NC+BSP and PC hens at 48 woa, with no difference between diets at either of the other ages (P = 0.036). Total BMD in the femur mid-diaphysis was higher in the NC hens than in the NC+BSP and PC hens at 48 woa, but higher in NC+BSP hens than in the NC hens at 70 woa, with no difference due to diet at 32 woa (P = 0.032). The AIDP was higher in the NC+BSP hens than in NC hens and intermediate in the PC hens at 32 woa (P = 0.034). However, the AIDP was higher in each of PC and NC hens than in NC+BSP hens at 70 woa (P = 0.028). The AIDCa was higher in the PC hens than in NC+BSP hens at 48 woa and intermediate in NC hens (P = 0.037) but was not affected by diet at other ages.
Overall, the lack of diet effects on performance, eggshell quality, and the majority of the assessed bone trait parameters and the lack of differences between PC and NC diets on AIDP and AIDCa strongly suggest that the avP and Ca in the NC diets were not deficient. The sufficiency of the NC diet demonstrates that the primary breeder recommendations include considerable safety margins, and limited the opportunity for supplemental BSP to alleviate adverse effects of P and Ca reductions. Also, the sensitivity and the additional information provided by bone densitometry relative to bone ash and breaking strength in evaluation of effects of dietary avP and Ca levels and supplemental phytase on bone quality of laying hens was established. The overall findings of this study emphasize that dietary Ca and avP levels in commercial layers should be re-evaluated, especially when supplemented with exogenous phytase.