ABSTRACT This study evaluated the potential of incremental doses of an enhanced Escherichia coli-derived phytase to support step-wise reduction of supplemental inorganic phosphate in an all-vegetable broiler diet. Corn-soybean meal-based diets containing 0.40/0.80%, 0.35/0.70%, and 0.30/0.60% avP and Ca, respectively from 0-10, 10-25, and 26-42 days posthatch served as experimental control (PC). Three test diets were formulated with 500, 1000, and 1500 FTU/kg of phytase assigned respectively an avP matrix of 0.15, 0.19, and 0.23% and a fixed Ca matrix of 0.15%. An additional diet (PC++) containing extra avP and Ca (+0.05% avP/+0.1% Ca) to that of PC was included to test if avP and Ca were not limiting in PC. Each diet was offered to 16 replicates of straight-run broilers kept in floor pens (30 birds per pen). PC++ had lower (p<0.05; 10 and 25 d) or similar (42 d) BW and toe ash compared with PC confirming the avP and Ca set in PC were sufficient to support optimal growth and bone mineralization. Compared to the PC, diets containing 1000 and 1500 FTU phytase had higher BW (p<0.05) at 10 and 25 d. For the overall period of 0-42 d, FI, BW and FCR did not differ across treatments. Percentage-, but not the absolute-, toe ash at phytase treated groups was significantly (p<0.05) low compared with the PC. The experiment demonstrated that 1500 FTU/kg of enhance E. coli phytase supports optimal BW and FCR of broilers fed corn-soy diet largely void of supplemental inorganic phosphate.

Abstract: Exogenous phytase could influence dietary protein availability by variation in using dose. The objective of the present study was to determine if incremental dosing of an evolved E.coli 6-phytase would lead to improvements in lysine availability through evaluating performance and bone status in Bovans White layers. A total of 182 layers were placed in individual cages and distributed to 13 treatments: a 3 × 4 factorial arrangement with three levels of digestible lysine (dLys - 0.67, 0.77, and 0.87 %) and four doses of phytase (0, 300, 1 200, and 4 800 FTU/kg) in 0.12 % available P (avP) diets. Additionally, one phytase-free control treatment was included with 0.25 % avP and 0.87 % dLys. Productive parameters were recorded for 25 weeks, from 39 week-old. At the end, abdominal fat deposition and the tibia were sampled; in bone was determined breaking strength and bone ash. Layers fed 1 200 FTU/kg phytase increased egg production percentage (F3,169= 2.01, p = 0.111), abdominal fat deposition (F3,169= 2.52, p = 0.059), bone breaking strength (F3,169= 4.29, p = 0.006) and bone ash weight (F3,169= 3.62, p = 0.014) compared with non-phytase inclusion. Furthermore, 1 200 FTU/kg phytase decreased incidence of broken eggs and soft-shell eggs (F3,169= 2.9, p = 0.036). Phytase and dLys levels influenced egg mass and bone ash concentration (F12,169= 1.86, p = 0.043). FCR and body weight loss was reduced with phytase inclusion (respectively: F12,169= 2.43, p = 0.006, and F12,169= 2.24, p = 0.012). Phytase-free control diet increased egg weight (F12,169= 3.70, p < 0.001), but gave greater BW loss (F12,169= 17.79, p < 0.001), less abdominal fat content (F12,169= 5.85, p < 0.001), and no effect on other variables (p > 0.07). In conclusion, 1 200 FTU/kg of phytase improved productive performance and preserved body weight and bone status, without equivalence of phytase inclusion for dLys level, even with higher doses.

An experiment was carried out to evaluate different criteria in feed formulation based on digestible amino acids for broilers during the grower phase. Diets were formulated according to the recommendations for digestible methionine, methionine + cysteine, lysine, and threonine. A total number of six hundred Cobb 500 male day-old chicks were distributed in a completely randomized experimental design, with three formulation criteria supplying the recommendations established by Baker & Chung (1992), Degussa (1997), and Rostagno et al. (2000), with 4 replicates of 50 birds each. No significant differences were observed for weight gain and feed intake. However, feed conversion ratio improved when birds were fed the diets containing the profiles recommended by Baker & Chung (1992) and Degussa (1997). No difference was observed in terms of leg, wings, back, and head yields. Broilers fed with the profile of Baker & Chung (1992) presented worst breast yield, whereas those fed the Degussa (1997) standard had better carcass yield.