The effect of increasing metabolizable energy levels in broiler feeds in the phases of 22 to 35 and 36 to 42 days

Introduction

Even though not a nutrient, energy promotes considerable modifications in birds' performance and feeding behavior. High energy levels promote, in accordance with Macari et al. (1994), an alteration in bird's body composition, so that controlling/assuring adequate metabolizable energy (ME) levels in broiler diets is necessary in order to prevent efficiency disorders. With the above in mind, the purpose of this study was to evaluate the effect of Me levels in broiler feeds, in the phases from 22 to 35, and from 36 to 42 days of age.

Materials and Methods

The experiment was undertaken in the Poultry Module, CCA, UFPB, Areia, PB, Brazil, with a total of 720 22-day-old broilers, distributed as per a completely-at-random design with 6 treatments and six 20-bird repetitions each. Birds were evaluated in the phases from 22 to 35 and from 36 to 42 days of age.

At study completion, 3 birds per experimental unit were killed in order to obtain carcass part weights/yields. The following parameters were evaluated: performance, carcass part yield, and economic evaluation, considering feed cost as the only variable cost.

The feeds were formulated to fulfill the recommendations suggested by Rostagno et al. (2005) for broilers at this ages. Increasing ME levels were used in the scale of 100 Kcal/Kg feed, so that the rations from 22 to 35 days contained 2,900, 3,000, 3,100, 3,200, 3,300 and 3,400 kcal/kg, while in the phase from 36 to 42 days the ME levels were 2,950, 3,050, 3,150, 3,250, 3,350 and 3,450 kcal/kg feed. Results were analyzed by polynomial regressions.

Results and Discussion

Table 1 shows the performance results.

Table 1. Effect of metabolizable energy (ME) on feed intake (FI, g/bird/day), weight gain (WG, g/bird) and feed conversion rate (FCR, g/g) of broilers in the phases evaluated

ME	22 - 35 days	36 - 42 days	22 - 42 days
(kcal/kg)	FI	WG	FCR	FI	WG	FCR	FI	WG	FCR
2,900/2,950	2,243.83	1,284.82	1.75	1,428.08	666.81	2.14	3,671.92	1,969.28	1.87
3,000/3,050	2,221.25	1,292.53	1.72	1,441.00	713.33	2.02	3,662.25	2,009.00	1.82
3,100/3,150	2,237.83	1,307.52	1.71	1,486.75	759.83	1.96	3,724.58	2,048.02	1.82
3,200/3,250	2,197.58	1,333.67	1.65	1,427.83	754.72	1.89	3,625.42	2,108.72	1.72
3,300/3,350	2,200.00	1,346.68	1.63	1,445.00	732.67	1.97	3,645.00	2,091.02	1.74
3,400/3,450	2,121.25	1,344.93	1.58	1,392.31	708.50	1.97	3,513.56	2,075.30	1.69
Effect	L*	L*	L*	Q*	Q*	Q*	-	-	-
Estimate	-	-	-	3,119.3	3,294.4	3,375.0
CV (%)	2.47	2.57	2.79	2.63	3.23	3.30	1.95	3.01	2.35

^{CV (%): coefficient of variation; L*: linear effect at 5% probability; Q*: Quadratic effect at 5% probability.}

As shown in Table 1, in the 22 - 35 day phase, increasing the dietary ME level resulted in significant linear effects on feed intake (Ŷ=-0.2048x + 2848.9; R²:0.74); weight gain (Ŷ=0.1398x + 878.09; R²:0.94) and feed conversion rate (Ŷ=-0.0003x + 2.7226; R²:0.95) nevertheless, in the later phase the effects on feed intake (Ŷ=-0.0008x² + 4.9908x - 6422.3; R²: 0.65), weight gain (Ŷ =-0.0011x² + 7.2478x - 10961; R²: 0.96) and feed conversion rate (Ŷ =0.000002x² - 0.0135x + 24.063; R²:0.92) were quadratic.

In the phase from 22 to 35 days of age, broiler performance improved as dietary ME increased. Possibly, the ME levels used in this phase caused no excess over the nutritional requirement whatsoever, suggesting that, in this particular phase, the broilers would require higher levels than those used herein. Nevertheless, in the final phase, a significant, quadratic response was observed, showing that the levels used in this study corresponded and fulfilled to a certain level the nutritional requirements of broilers, under the conditions of this study.

Table 2 shows the results of carcass yield, organ yields, and part yields.

Table 2. Effect of the treatments on carcass yield (%), breast yield (%), thigh yield (%), leg yield (%), heart (%), gizzard (%), liver (%) and abdominal fat (%)

ME (kcal/kg)	Carcass	Breast	Thigh	Leg	Heart	Gizzard	Liver	Abdominal fat
2,900/2,950	88.27	27.40	9.77	11.95	0.497	2.16	1.65	1.17
3,000/3,050	86.62	30.65	10.68	12.56	0.548	2.48	1.73	1.38
3,100/3,150	85.86	30.85	10.51	12.45	0.542	2.36	1.73	1.36
3,200/3,250	87.20	30.62	10.63	12.33	0.559	2.37	1.70	1.32
3,300/3,350	86.68	29.69	10.75	12.77	0.547	2.47	1.71	1.48
3,400/3,450	86.92	28.93	10.60	13.66	0.574	2.50	1.77	1.64
Effect	ns	ns	ns	ns	ns	ns	ns	L*
CV (%)	2.44	7.71	8.33	8.92	8.58	18.37	8.45	8.44

^{ns: not significant; CV (%): coefficient of variation; L*: linear effect (Ŷ = 0.0007x - 1.0008; R2: 0.79).}

Table 2 shows that only abdominal fat was influenced by the dietary ME levels. Macari et al. (1994) found that increasing dietary ME levels in broilers cause body composition alterations, since excess intake of energy sources is reflected in a higher fat deposition in the adipocytes. This way, as seed in our study, increasing feed ME energy resulted in increased abdominal fat, and reduced carcass yield even when this variable was not statistically affected. Tables 3 and 4 show the economical evaluation results, and production index, respectively.

Table 3. Effecto of metabolizable energy on economic parameters

Variables	Treatments
1	2	3	4	5	6
Feed intake, kg/trat	220.31	219.74	223.47	217.52	218.70	210.81
Cost per ton of feed, US$/ton	544.18	542.80	565.66	620.89	675.93	730.61
Cost per kg of feed, US$/kg	0.54	0.54	0.57	0.62	0.68	0.73
Cost of feed, US$/trat	119.89	119.27	126.41	135.06	147.83	154.02
broiler produced, kg/trat	168.79	169.38	173.09	177.93	175.35	175.12
Cost broiler produced, US$/kg	0.71	0.70	0.73	0.76	0.84	0.88
Broiler price, US$/kg	1.96	1.96	1.96	1.96	1.96	1.96
Breast production, kg/trat	46.25	51.91	53.40	54.48	52.06	50.66
Breast cost, US$/kg	2.59	2.30	2.37	2.48	2.84	3.04
Breast price, US$/kg	3.90	3.90	3.90	3.90	3.90	3.90
Thigh production, kg/trat	16.49	18.09	18.19	18.91	18.85	18.56
Thigh cost, US$/kg	7.27	6.59	6.95	7.14	7.84	8.30
Thigh price, US$/kg	2.15	2.15	2.15	2.15	2.15	2.15
Leg production, kg/trat	20.17	21.27	21.55	21.94	22.39	23.92
Leg cost, US$/kg	5.94	5.61	5.87	6.16	6.60	6.44
Leg price, US$/kg	2.70	2.70	2.70	2.70	2.70	2.70
Gross Rent, US$	601.11	630.78	644.80	661.14	647.71	645.32
Gross Profit, US$	481.22	511.51	518.39	526.08	499.89	491.30
Relative Gross Profit, %	100.00	106.29	107.72	109.32	103.88	102.09

In the economic evaluation of the results shown in Table 3 total broiler produced was used and, in accordance with yields, the production of breast, thigh, and leg were calculated. As per the results of relative gross profit, all the feeds with levels above the treatment with the lowest ME content resulted to be better in such variable, whilst T4 resulted in the best economic returns, even higher than T1 in 9.32%.

Table 4. Per-treatment relative gross margins

Variables	Treatments
1	2	3	4	5	6
Mortality, %	1.67	1.67	3.33	1.67	-	1.67
Viability, %	98.33	98.33	96.67	98.33	100.00	98.33
Weight gain, kg	1.97	2.01	2.05	2.11	2.09	2.08
Feed conversion rate, kg/kg	1.87	1.82	1.82	1.72	1.74	1.69
Production index	518.94	541.73	543.97	602.86	599.38	602.57

The production index (PI) shown in Table 4 was calculated only for the 20-day evaluation period. As shown in Table 4, T4 resulted in the highest PI, corroborating the highest relative gross profit described in Table 3.

Data from this study is consistent with that published by Sakomura et al. (2004), who evaluated the effects of various ME levels on broiler performance from 22 to 43 days of age, and found that as ME level increased, both weight gain and FCR experienced significant improvements.

Conclusion

Levels of 3,400 and 3,375 kcal/kg ME in the feed for broilers in the phases from 22 to 35 and from 36 to 42 days of age, respectively, are recommended.

Bibliography

Macari M, Furlan RL, Gonzales E. 1994. Fisiologia aplicada a frangos de corte. Jaboticabel:FUNEP/UNESP. 296pp.

Rostagno HS, Albino LFT, Donzele, JL. et al. 2005, Tabelas Brasileiras para Birds e Suínos: Composição de Alimentos e Exigências Nutricionais. 2ª ed. UFV/DZO. 186pp.

Sakomura NK, Longo FA, Rabelo CBV et al. 2004. Efeito dos níveis de energia metabolizável da dieta no desempenho e metabolismo energético de frangos de corte. Revista Brasileira de Zootecnia 33(3, supl1).