MATERIALS AND METHODS

One hundred and sixty unsexed day-old broiler chicks (vencobb) were randomly selected and distributed into five experimental groups, comprising two replicates of sixteen chicks each. They are, T_c control (3% CF without xylanase), T₁ (3% CF with xylanase), T₂ (3.5% CF with xylanase), T₃ (4% CF with xylanase) and T₄ (4.5% CF with xylanase). Xylanase supplemented at the rate of 10 g/100 kg feed. The experimental diets were formulated to meet or exceed BIS (1992) recommendations for all the nutrients (Table 1). Crude fiber content in broiler feed was raised to the respective level by incorporating De-Oiled Rice Bran (DORB). The corresponding energy and protein levels for the five experimental starter diets (T_c, T₁, T₂, T₃ and T₄) were 2921, 2921, 2893, 2872 and 2855 kcal kg^-1 and 21.58, 21.58, 21.59, 21.62 and 21.50%, respectively.

Table 1:	Percent ingredient composition of experimental diets
TM Mix* contained Fe SO4, Cu SO4, Zn SO4, Mn SO4, potassium iodide, sodium selenite and DCP as base, Premix** contained necessary vitamins, choline chloride, anticoccidial agents, emulsifiers and acidifiers, DORB: De-oiled rice bran

Similarly, the levels of energy and protein in finisher diets (T_c, T₁, T₂, T₃ and T₄) were 3018, 3018, 2991, 2962 and 2946 kcal kg^-1 and 19.91, 19.91, 19.70, 19.77 and 19.63%, respectively. All the rations were formulated to be is calorific and is nitrogenous. The enzyme tested was a commercial enzyme premix (Lumifeed xylanase) having the enzyme activity of 70,000 IU g^-1.

Weekly body weight of individual birds, replicate wise feed intake and livability were recorded. Feed conversion ratio was calculated on cumulative basis for each replicate. At the end of experiment, one bird from each replicate was randomly selected and slaughtered to study the carcass traits. The Protein Efficiency Ratio (PER) was calculated as the ratio of weight gain to total protein consumed. Experimental diets and DORB were estimated for the proximate principles as per the methods of AOAC (1990). Economic efficiency of live weight gain of broiler chicks was calculated based on the actual cost of individual feed ingredients during study period.

Statistical analysis: Data was analysed by using SPSS^TM VERSION (10.0). The Duncan range test was used to determine difference among treatment means for significant dietary effect (Snedecor and Cochran, 2004) with p<0.05 considered statistically significant unless otherwise noted.

RESULTS AND DISCUSSION

Body weight gain of broilers fed with treatment diet was greater than that of birds fed with the control diet. The improvement in the body weight due to enzyme supplementation might be attributed to degradation of fiber content of DORB. Raza et al. (2009) reported that addition of Grindazyme enzyme to diet containing 10% sunflower and 6% crude fibre significantly improved the body weight in broilers when compared to that of control group fed with same diet without enzyme. Feed intake was significantly (p<0.05) higher in treatment group compare to that of control group. Among the treatment groups highest feed consumption was recorded in T₄ followed by T₂, T₃ and T₁. This increased feed consumption in treatment groups can be justified as high crude fibre in the diet limits energy access and also the NSPs in the fibre contacts with water forms a gel that reduces passage time and absorption of nutrients and thus, increases feed consumption to compensate and meet nutritional demands (Tabeidian et al., 2011). Enzyme supplementation had no significant influence (p>0.05) on feed efficiency during the overall growth phase. Similarly, Jawale et al. (2006) reported that supplementation of enzymes did not have any significant influence over FCR of broilers. Though there was no significant (p>0.05) difference was noted in FCR among the various treatment groups some numerical improvement was recorded in T₁ group. Maximum mortality was observed in control group when compared to that of enzyme treated groups. Among the treatment groups highest mortality was observed in T₄. Use of high levels of fiber diets increased the incidence of sticky droppings in broilers (Pettersson, 1987) might be the reason for high mortality. There was no significant (p>0.05) difference in PER between the control and enzyme treated groups. However, some numerical improvement was recorded at high fiber diet fed birds which was comparable to that of control diet fed birds. Similar to FCR, the reason for improved PER could be due to enhanced bioavailability of nutrients in the enzyme supplemented group. The data on effect of enzyme supplementation on overall performance of broilers was presented in Table 2.

With regard to slaughter characteristics, dressing percentage was higher in groups fed on enzymatic diet than the control. This finding is supported by Khan et al. (2006) and Medhi et al. (2003) found that enzyme supplementation to fibrous diet improved the growth rate and thereby increased the dressing percentage.

Table 2:	Effect of experimental diets on performance parameters of broilers at 6 weeks of age
a-d Values within columns with no common superscripts are significantly different (p<0.05)

Table 3:	Carcass characteristics of broilers fed on experimental diets
a-d Values within columns with no common superscripts are significantly different (p<0.05)

Table 4:	Cost benefit analysis of broiler production
a-dValues within columns with no common superscripts are significantly different (p<0.05), Fixed cost*: Cost of chick+transportation cost+medicine and vaccination cost+labour charges

Similarly Rahman et al. (2005) showed that broiler fed on parboiled rice polish based diet supplemented with multi enzyme improved the dressing percentage. No significant (p>0.05) difference was noticed in breast muscle yield and abdominal fat pad percentage in all treatment groups compared to that of control group. Whereas, thigh muscle percentage and giblet weight were significantly higher (p<0.05) in treatment groups than that of control group (Tc). Similarly Wu and Ravindran (2004) found that enzyme supplementation had no effect on abdominal fat pad in broilers. The data on carcass yield of different dietary treatment groups are shown in Table 3.

Margin of profit was calculated with the help of cost benefit analysis. The economics of feeding higher fibre rations supplemented with xylanase enzymes are presented in Table 4. The results revealed that per bird total return on sale for T_c, T₁, T₂, T₃ and T₄ was Rs. 113.4, 118.3, 116.9, 116.9 and 116.9 at total expenditure of Rs. 83.68, 84.75, 85.04, 83.75 and 83.61, respectively. Net expenditure was varied slightly among experimental groups. This variation occurred mainly due to variation in feed intake, variation in feed cost (per kg) and variation in mortality in different groups. Among the treatment groups, net profit (Rs/kg body weight gain) was highest on T₄ (Rs. 19.93) followed by those of T₃ (Rs. 19.85), T₁ ( Rs. 19.85), T₂ (Rs. 19.07) and T_c (18.34). Enzyme supplementation to high fiber diet (T₄) saved 1.59 paise per kg live weight production of broilers. It was concluded that supplementation of xylanase in high fiber diet may have better cost benefit ratio than that of low fiber diet without xylanase. The result obtained in the current experiment are in agreement with the findings of Srivastava et al. (2005) and Jawale et al. (2006) reported reduced feed cost for improved feed utilization and faster growth rate of broilers fed with enzyme supplemented high fiber diet. Similarly Oladunjoye and Ojebiyi (2010) found that supplementation of Roxazyme G2G enzyme to the rice bran diet at 20% inclusion level reduced the feed cost per kg live weight gain.

CONCLUSION

It was concluded that maintaining the maximum fibre level of Bureau of Indian Standards along with incorporation of xylanase as fibre degradable enzyme in broiler feed resulted in positive effect on growth performance of broilers and better cost benefit ratio when compared to that of low fibre diet without xylanase.