Heat-Resistant Bacterial Phytase in Broiler Pelleted Diets

published in the proceedings of the 2nd Congress on Additives in Animal Feed CBNA/2012, Brazil


IntRoduCtIon
Enzymes are protein that play specific roles in biochemical reaction, and are macromolecules known for their extraordinary specificity and catalytic power.Among exogenous enzymes studied and utilized in monogastric diets, phytase is applied to increase the availability of nutrient present in complexes with the phytate molecule of plant feedstuffs (Dari, 2004).Moreover, phytase reduces the environmental impact caused by excessive phosphorus excretion (Bess et al., 2006), contributing for the sustainability of poultry production.
The objective of the study was to evaluate the effects of a heatresistant bacterial phytase added to pelleted diets on mineral digestibility, live performance, carcass traits, and bone quality of broilers.

MAteRIAl And MethodS
The experiment was carried out at the Center of Poultry Research of the School of Veterinary Medicine and Animal Science of Universidade de São Paulo, Pirassununga campus, Brazil.Two trials were performed: one to evaluate mineral digestibility and the other to evaluate broiler performance, carcass traits, and bone quality.
Mineral digestibility was evaluated using 240 one-d-old Cobb 500 broilers distributed according to a completely randomized experimental design consisting of three treatments (positive control; negative control, with 0.10 points reduction in calcium level and 0.15 points reduction in available phosphorus level; and negative control + phytase at 500 FTU/kg), with eight replicates of 10 birds each.Birds were housed in metabolic cages and reared from one to 21 days old.
The experimental diets were formulated to supply the nutritional requirements recommended by Rostagno et al. (2011) for the starter phase (1-21 days) and are presented in Table 1.The phytase product derived from the expression of the E. coli gene changed by mutagenesis to make the molecule resistant to pelleting temperature.The positive control feed was supplied to all birds until they were 13 days old.On day 14, the experimental diets started to be fed until day 21, with five days of adaptation and three days of total excreta collection.
At the end of the trial, the feces collected per replicate were homogenized, and a sample was remover, weighed, and pre-dried in a forced-ventilation oven at 65ºC for 72h.Samples were exposed to air until they reached environment temperature and humidity.Samples were then weighed, ground, properly packed, and submitted to the laboratory for calcium and phosphorus analyses, together with the experimental diets.Data were analyzed using the GLM procedure of SAS ( 2001) statistical package and means were compared by the test of Tukey at 5% significance level.
Live performance, carcass traits, and quality were evaluated using 350 one-d-old Cobb 500 broilers distributed according to a completely randomized experimental design consisting of three treatments (positive control; negative control, with 0.10 points reduction in calcium level and 0.15 points reduction in available phosphorus level; and negative control + phytase at 500 FTU/kg), with eight replicates of 15 birds each.Birds were housed in 24 floor pens and reared from one to 42 days old.
The experimental diets were formulated to supply the nutritional requirements recommended by Rostagno et al. (2011).Three feeding phases were applied: starter (1-21 days), grower (21-33 days), and  finisher (33-42 days), and are presented in Table 1.The phytase product derived from the expression of the E. coli gene changed by mutagenesis to make the molecule resistant to pelleting temperature.
Birds and feeds were weighed on days 1, 21, and 42 to determine feed intake, weight gain, and feed conversion ratio.At the end of the experiment, when broilers were 42 days old, two birds per replicate were sacrificed to determine carcass, breast, and leg yields.The right tibiae were collected for the analyses of calcium, phosphorus, and ash contents.Data were analyzed using the GLM procedure of SAS ( 2001) statistical package and means were compared by the test of Tukey at 5% significance level.

ReSultS And dISCuSSIon
The results presented in Table 2 show that the applied treatments did not influence ash or calcium excretion (p>0.05).However, when diets with phosphorus reduction were fed, excreta phosphorus content was also reduced when compared with the broilers fed the positive-control diet (p<0.05).The dietary addition of phytase promoted higher calcium and phosphorus retention relative to positive and negative control diet, as shown in Table 3.Ash retention was numerically different among treatments, with broilers fed the diet with phytase presenting higher retention, despite the lack of statistical difference (p>0.05).
These results are consistent with those reported by Dourado et al. (2006), who evaluated the effect of phytase supplementation to broiler diets on nutrient digestibility and found higher phosphorus retention in birds fed diets with phytase supplementation.This is in agreement with the findings of Fukayama et al. (2008) from a study on the effect of phytase supplementation on nutrient digestibility in broilers that calcium digestibility was not different during the phase of one to 21 days between birds fed reduced nutritional levels and supplemented with phytase and those fed the positive control diet.Broilers fed the diets with reduced nutritional levels presented lower phosphorus digestibility than those fed the positive control diet; however, the supplementation of phytase to the negative control diet improved phosphorus digestibility.
When evaluating the effect of the dietary supplementation of phytase on calcium and phosphorus digestibility in broilers, Lelis et al. (2010) obtained better phosphorus digestibility coefficient and higher phosphorus retention, as well as lower phosphorus excretion and higher tibial phosphorus content; however, calcium digestibility coefficient and tibial ash content was not statistically different.
Live performance results are presented in Table 4.Although phytase supplementation numerically improved broiler performance when compared to the negative control diet, results were not statistically different among treatments (p<0.05).Carcass quality parameters were not influenced by the treatments (Table 5).Broiler tibial calcium content was not influenced by the evaluated diets (Table 6).However, dietary phytase supplementation increased tibial ash content when compared with the negative control diet.Broilers fed the diet supplemented with phytase presented similar tibial phosphorus content compared with those fed the positive control diet and higher compared with those fed the negative control diet (p<0.05).Shiroma NN, Dari RL, Baolin G, Yongcheng W, Araújo CS da S, Araújo LF The obtained results are different from those found by Laurentiz et al. (2005), who observed that broilers fed diets containing phytase and reduced phosphorus levels did not present higher mineral deposition in the tibia, but that tibial ash and phosphorus contents were reduced when a diet containing reduced phosphorus levels was fed.

ConCluSIonS
The supplementation of phytase to broiler diets increased dietary calcium and phosphorus digestibility, and consequently, improved bone quality.

Table 1 -
Ingredients and nutritional composition of the experimental diets.

Table 2 -
Excretion of nutrients in broilers fed the experimental diets.

Table 3 -
Retention of nutrients in broilers fed the experimental diets.

Table 4 -
Live performance of 1-to 42-d-old broilers fed the experimental diets.

Table 5 -
Carcass traits of broilers fed the experimental diets.

Table 6 -
Ash, calcium, and phosphorus tibial contents of broilers fed the experimental diets.