Menu
Phytate, a P storage compound in plants is not well used by chickens as a source of P because of limited endogenous phytase in the digestive tract. Exogenous phytase has been used in poultry diets to liberate P and other minerals such as Ca. Research studies on phytase use are well documented in broilers, but very little work has been carried out on laying hens. The objective of the present study was to determine the effects of phytase supplementation in diets with substantially reduced aP and Ca on eggshell and bone quality and ileal digestibility of P and Ca in laying hens from 25 to 37 wk of age. We hypothesized that eggshell and bone quality would decrease in hens fed with a reduced aP and Ca levels in the negative control (NC) diet and that phytase supplementation would increase eggshell and bone quality to the level of the positive control (PC) diet.
Eighty-four Lohmann LSL-Lite laying hens aged 25 wk, hens were weighed and randomly assigned to 1 of the 7 dietary treatments. Birds were checked and eggs were collected and recorded twice daily. Feed and water were provided ad libitum throughout the experiment. The experimental period lasted 12 wk from 25 to 37 wk of age. The corn–soy–canola meal–based experimental diets provided approximately 2,800 kcal/kg ME. Seven experimental diets were fed as mash in 2 dietary phases: start-lay diets from 25 to 28 wk of age and layer phase I diets from 29 to 37 wk of age. Diet 1 was a PC diet with 0.45% aP, 3.70% Ca, and 0.16% Na from 25 to 28 wk of age and 0.38% aP, 3.73% Ca, and 0.15% Na from 29 to 37 wk of age. Diet 2 was a NC, diet similar to the PC diet but reduced to 0.22% aP, 3.00% Ca, and Na 0.13% from 25 to 28 wk of age and to 0.19% aP, 3.02% Ca, and 0.13% Na from 29 to 37 wk of age. Diets 3, 4, 5, and 6 were the NC diets supplemented with phytase at 150 (NC + 150), 300 (NC + 300), 600 (NC + 600), and 1,200 (NC + 1,200) phytase unit (FTU)/kg, respectively. Diet 7 was the PC diet supplemented with phytase at 1,200 FTU/kg (PC + 1,200). Individual body weights were measured on a 4-week basis from 25 to 37 wk of age. Feed intake (FI) was recorded during each. Eggs were collected twice daily, at 4-week intervals, eggs were weighted, specific gravity and eggshell thickness (mm) were measured. Bone Characteristics were measured through in vivo bone scanning of the shank. At 37 wks of age hens were euthanized and femurs were subjected to a bone breaking strength (BBS) and ash evaluation. Digesta was collected for Phosphorus and Calcium Digestibility Assays.
Body weight, FI, FCR, and egg production were not affected by the diet × age interaction or diet main effect. Hen-day egg production, total egg number, or egg weight were not affected by dietary treatments. There were no diet × age interactions for egg SG or eggshell thickness. The NC + 1,200 had greater egg SG than the NC (1.090 ± 0.001 vs 1.088 ± 0.001 g/cm3; P = 0.004). Eggshell thickness was not affected by diet. No diet × age interactions were observed for in vivo bone mineral density (BMD), bone cross-sectional area, or bone mineral content (BMC) of the total, cortical, and trabecular + medullary bone tissues. However, the PC hens had greater total BMD than those of the NC, the NC + 300, the NC + 600, and the NC + 1,200 hens (P < 0.001). The PC hens also had higher cortical BMD than the NC, the NC + 300, and the NC + 600 hens (P < 0.001). A decrease in trabecular + medullary BMD was observed in the NC, the NC + 150, and the PC + 1,200 relative to the PC treatment (P = 0.004). At 25 wk of age, total BMD was higher than at 33 and 37 wk of age (P < 0.001). At 37 wk of age, the AID of P in the NC hens was lower than in the NC + 600 and the NC + 1,200 hens (P = 0.024). Hens fed the NC diet had lower AID of Ca than the other treatments except the NC + 150 (P = 0.010).
Overall, the reduction of aP and Ca in the NC diet did not cause any adverse effects on performance, production, and eggshell quality in laying hens over the 12 wk of the study. The current recommendations for Ca and aP provided by the primary breeders are likely substantially higher than actually required by hens. From a bone biology standpoint, the NC hens started mobilizing bone at the end of the trial, resulting in decreased BMD and BMC; however, this did not appear to cause osteoporosis or other bone problems. The increase of P and Ca digestibility by phytase supplementation resulted in some but inconsistent increases in bone measures. The implications of longer term feeding of the NC diet to determine the efficacy of phytase in laying hens should be studied further. Short-term phytase studies should be designed with further reductions in Ca and aP to adequately asses the efficacy of phytases, while minimizing the risk of severe bone issues.