MATERIALS AND METHODS

Experimental design: A total 320 one-day-old male Ross 308 chickens were arranged in a completely randomized design experiment and randomly allocated into five dietary treatments with 64 birds per treatment. The chickens in each treatment were further divided into four replicates with sixteen chickens and housed in pens of identical size (1.5x1.5 m, each broiler had about 0.14 m² spaces) in a deep litter system with study paper roll floor. Light was provided 24 h continuously with overhead incandescent lighting during the 42 day period of the experiment. The room was thermostatically controlled with temperatures maintained at 32°C for the first week and a three degree reduction in temperature every week afterwards. The birds were given an anti-stress agent from the first day of age and before, during and after the vaccinations. In order to raise their control pathogens they were vaccinated against bronchitis on days 1 and 9, Gumboro disease on days 15 and 21 and for Newcastle disease on day 9 of the experiment. The kaolin and zeolite used in this study were excellent processing to decrease metal oxide content and the chemical composition of them is demonstrated in Table 1.

Dietary treatments: (1) Control (diet without kaolin and zeolite), (2) Diet with inclusion of 15 g kg^-1 kaolin, (3) Diet with inclusion of 30 g kg^-1 kaolin, (4) Diet with inclusion of 15 g kg^-1 zeolite and (5) Diet with inclusion of 30 g kg^-1 zeolite. The chicks were fed a commercial feed starter (corn and soybean based), contained 20.85% Crude Protein (CP), 2900 kcal ME kg^-1, 0.91% calcium and 0.41% available phosphorus which fed to broilers up to 21 days. The grower diets contained 18.75% CP, 3000 kcal ME kg^-1, 0.84% calcium and 0.33% available phosphorus which fed to broilers up to 42 days. All of the experimental diets during starter and grower periods were isonitrogenic and isocaloric and chicks were allowed access to the diets and water ad libitum.

Collection and analysis of samples: Five litter samples were obtained at days 14, 28 and 42 from each pen from the same area from which the moisture, pH, Nitrogen (N), ash, Calcium (Ca) and Phosphorus (P) concentration were measured. Litter samples were taken by removing the first 10 mm of the exposed surface after the top layer had been removed from centre and four corners of each pen.

Table 1:	Chemical composition of kaolin and zeolite

The samples from each pen were mixed and homogenized to make one sample and were refrigerated before taken up to the laboratory for analyses. Moisture content of samples was determined by placing them in an oven 105°C for 24 h until achieves a constant weight. Litter pH content was measured at days 14, 28 and 42 of experiment by using a pH meter (Model WTW-720 Inolab., Germany). The milled samples were then analyzed for N and ash contents using the procedures described by the AOAC (2005). The percentages of litter calcium and phosphorus were determined by colorimetric and spectrophotometric, respectively according to AOAC (2005) methods.

Statistical analysis: The results of every determination were analyzed using the general linear model procedure of the SAS (SAS Institute, 2003). Duncan’s multiple range test was used to compare significant means and the level of differences were considered significant at p<0.05 (Duncan, 1955).

RESULTS AND DISCUSSION

The effects of experimental treatments on litter moisture and pH are given in Table 2. Litter moisture content did not differ significantly (p>0.05) between treatments on days 14 and 28, whereas at day 42 Litter moisture content in control diet (33.68%) was significantly (p<0.05) higher compared to diet containing 30 g kg^-1 kaolin and zeolite i.e., 28.00 and 27.17%, respectively. These results are in agreement with previous studies in that silicate minerals significantly reduced litter moisture content in broiler chickens houses (Kiaei et al., 2002; Karamanlis et al., 2008; Tatar et al., 2012). Aluminosilicates have a high capacity for swelling and absorbing water and ammonia and can improve litter condition (Ramos et al., 1996). Litter moisture plays an important role in litter quality and in a broiler house with correctly managed, litter moisture normally averages between 20-35%. Increasing the litter moisture content and temperature are two main factors that enhance ammonia volatilization from broiler litter (Miles et al., 2011). Butcher and Miles (2012) reported that well managed litter and kept moisture content within the admitted range can reduced disease or other production problems. The litter pH of treated group on days 28 and 42 of experiment were decreased compared to control group but these differences were not statistically significant (p>0.05).

Table 2:	Effects of experimental treatments on litter moisture and pH
Means within columns with no common superscripts are significantly different (p<0.05)

Table 3:	Effects of experimental treatments on litter nitrogen and ash
Means within columns with no common superscripts are significantly different (p<0.05)

No significant differences in pH content of the broiler litter due to dietary silicate minerals supplementation in the present study is in agreement with some earlier studies (Maurice et al., 1998; Loch et al., 2011; Safaeikatouli et al., 2011).

The nitrogen and ash content of litter in broilers supplemented with kaolin and zeolite in diets are shown in Table 3. Litter nitrogen content on day 14 and day 42 was significantly (p<0.05) lower in treatments containing 30 g kg^-1 kaolin and zeolite compared to control treatment. Litter nitrogen content on day 28 did not show any significant (p>0.05) difference between experimental treatments. Result further showed that control diet has highest nitrogen content of litter during the days 14, 28 and 42 (2.62, 3.05 and 3.99%, respectively). On the other hand, treatment containing 30 g kg^-1 kaolin on days 14 and 28 and treatment with 30 g kg^-1 zeolite on day 42 have lowest nitrogen content of litter (2.29, 2.74 and 3.71%, respectively). This finding is in agreement with the result of Tatar et al. (2012) that showed litter nitrogen content in diet containing high level of zeolite (4%) decreased significantly compared to diet supplementation with low level of zeolite (2%) and control. High nitrogen levels in the broiler litter can increase NH₃ in the poultry house that lead to reduce broiler performance and health and use of some litter additives can decrease these nitrogen levels. Zeolite is a cation-exchange composition that has high ability for absorb NH⁺₄ ions because of its hydrated properties resulting from its structures (Mumpton and Fishman, 1977).

Previous studies show that the use of aluminosilicates in broiler diet would decrease ammonia concentration in poultry houses (Amon et al., 1997; Li et al., 2008; Loch et al., 2011). Ash content of litter showed no significant differences between dietary treatments and control (p>0.05).

Nevertheless litter ash content in treatments with kaolin and zeolite on day 28 and day 42 was numerically better in comparison to control diet. Cabuk et al. (2004) suggested that the addition of zeolite in broiler diet led to decrease in fecal crude ash.

Table 4:	Effects of experimental treatments on litter calcium and phosphorus
Means within columns with no common superscripts are significantly different (p<0.05)

Table 4 shows the effects of dietary treatments on Ca and P content of litter. Result showed that the Ca content of litter on days 14 and 28 in control diet (4.26 and 6.45%, respectively) was significantly (p<0.05) higher as compared to treatment containing 30 g kg^-1 zeolite (3.41 and 5.59%, respectively). Litter Ca content did not differ significantly (p>0.05) among experimental treatments on days 42. In diet containing kaolin and zeolite litter P content during the overall period (days 14, 28 and 42) was lower than control diet but this difference was numerically not statistically (p>0.05). Herzig et al. (2008) and Safaeikatouli et al. (2012a) reported that adding 3% of zeolite to broiler diet can increase Ca content in blood and tibia and did not any significant effect on P content. Therefore, it can be concluded that zeolite might enhance absorption of Ca and decrease excretion of it.

CONCLUSION

It is concluded that using kaolin and zeolite in broiler chicken diets caused decreased content of moisture, nitrogen and calcium in broiler litter as well as can reducing environmental pollution. Thus, kaolin and zeolite can be use as a feed additive in the broiler chickens diet for improving litter quality and performance.