Safety And Efficiency Evaluation Of Phytase Transgenic Corn In Laying Hens

Three experiments were conducted to evaluate safety and efficiency of phytase transgenic corn (PTC) used as a feed ingredient in laying hens. The effect of PTC on the laying performance, egg quality, organ development, serum parameters, immune response and intestinal microflora of laying hens were studied and transgenic corn DNA fragments and proteins were detected in digesta, blood, tissues, and eggs of laying hens. Furthermore, we compared the effect of transgenic corn derived-phytase and two microbial phytases on the laying performance, egg quality, ileum nutrient digestibility, and bone mineralization in laying hens fed a low-P corn-soybean diet.Exp.l was conducted to evaluate the compositional and nutritional equivalence of PTC and isogenic conventional corn (CC) in roosters. Following a48h fasting period, sixteen roosters were given50g of each sample via crop intubation and excreta were collected for48h. N-free and P-free diets were used to evaluate endogenous amino acid and endogenous P losses, respectively. Chemical composition was not different between PTC and CC, whereas the phytase activity for PTC was greater than CC(P<0.001). No difference was observed in the true metabolizable energy (TME) and true amino acid availability (TAAA) values between the PTC and CC in roosters. The true P utilization for PTC was greater than CC (37.92vs.55.85%;P<0.001), and CC and PTC contained0.13and0.18%available P (AP, DM basis,P<0.001), respectively. The results of this study indicated that the chemical composition, TME and TAAA in PTC are essentially equivalent to that in CC, and the true P utilization for roosters is higher in PTC than in CC.Exp.2was conducted to assess the effects of long-term feeding with PTC to hens on laying performance, egg quality, organ development, serum parameters, immune response and intestinal microflora, and investigate the fate of transgenic DNA and protein in digesta, blood, tissues, and eggs. Fifty-week old laying hens (n=144) were fed with a diet containing62.4%PTC or CC for16weeks. We observed that feeding PTC to laying hens had no adverse effect on laying performance or egg quality (P>0.05) except on yolk color (P<0.05). There were no observed adverse effects of the PTC on the serum parmeters, organ development, immune response, intestinal microbial community in laying hens (P>0.05). Transgenic phyA2gene and protein were rapidly degraded in the digestive tract and were not detected in blood, heart, liver, spleen, kidney, breast muscle, and eggs of laying hens fed with diet containing PTC. It was concluded that performance of hens fed diets containing PTC, as measured by egg production and egg quality, was similar to that of hens fed diets formulated with CC. There was no evidence of phyA2gene or protein translocation to the blood, tissues, and eggs of laying hens.Exp.3was compared the efficacy of transgenic corn-derived phytase (TCDP) and two other commercial microbial phytases (PA and PB) in a long-term feeding study of laying hens. The treatments consisted of a positive control (PC) diet adequate in P (0.32%NPP); a negative control (NC) diet low in P (0.10%NPP); and an NC supplemented diet containing three phytase sources (TCDP, PA and PB) at two supplemental levels (500and5,000FTU/kg of diet). Eight diets were fed to Hy-line hens (n=576) from50to66weeks of age. We found that with a reduction in dietary P in the NC diet, egg production, egg mass, feed intake, final BW, BW gain, shell thickness, and eggshell strength of laying hens decreased (P<0.05). In addition, the number of soft-shelled, cracked and broken eggs increased (P<0.05) in the NC group. The addition of TCDP, PA or PB significantly increased laying production and egg quality (P<0.05), and performed similarly in hens fed the PC diet. Hens fed each source of phytase had greater ileal P digestibility, tibia ash, and bone breaking strength than hens fed the NC diet (P<0.05). The residual phytase activities along the GIT had increased (P<0.01) with the addition of TCDP, PA and PB to the NC diets. The TCDP had higher residual activity (P<0.05) in the crop, proventriculus and gizzard, jejunum, and ileum as compared to the PA and PB activity. There was a decrease (P<0.01) in the phytate P content of the digesta from all sources of phytase supplementation in the NC diets. Residual phytate P content decreased caudally along the GIT of hens. The ileum P digestibility increased as phytase level increased from500to5,000FTU/kg of diet (P<0.05). Results from this study indicate that the addition of a novel TCDP to a P-deficient diet improves laying performance, egg quality, ileum P utilization, and bone mineralization, and TCDP is as efficacious as two commercial microbial phytases when P-deficient diets for laying hens were supplemented with it.In conclusion, no adverse effect was found when the phytase transgenic corn was used in laying hens diet in the series of experiments. There was no evidence of phyA2gene or protein translocation to the blood, tissues, and eggs of laying hens. TCDP is as efficacious as two commercial microbial phytases in P-deficient diets for laying hens.