The effects of feeding broiler chickens growing and finishing complete feeds of lowered energy value

¹Ryszard K. Pisarski, ²Krzysztof Szkucik

^1- Institute of Animal Nutrition, ^2- Department of Food Hygiene of Animal Origin

Agricultural University, 20-950 Lublin, Akademicka 13 St.

During the last few years a tendency to lower energy level (density) in the complete feeds for broiler chickens becomes more and more popular. It is believed beneficial for animal welfare (protection against cardiovascular diseases and sudden death syndrome) and for consumers of poultry meat as well.

Material and methods

The research was carried out using Cobb broilers kept in cages under regular environmental conditions. 144 one-day-old chicks were randomly allocated into control (C) and experimental (E) groups consisting of 3 replications each. During the starting period (1-21d) all the broilers were fed identically (20.5% crude protein, 3065 kcal ME/kg). In the consecutive growing (22-35d) and finishing (36-slaughter) phases the nutrition was alternated: the control broilers were fed standard concentrates (19.5% c.p. and 3200 kcal ME), whereas experimental birds were given feeds containing 19.5% c.p. and 2900 kcal ME. The nutritive value of growing and finishing feeds was identical but finishers contained no coccidiostat.

To avoid a potential effect of broilers body weight on the examined characteristics, the control birds were reared till 42^nd and the experimental ones - till 47^th day of age. On the last day of experiment 8 chickens (4 ♂ and 4 ♀) of the body weight as close to the average as possible were selected from each group, sacrificed and dissected. The left moiety of a breast muscle and the left thigh muscles were used for a sensory evaluation of meat (odour, tenderness and juiciness). The right part of the breast muscle and the right thighs were analysed to establish crude protein and intramuscular fat (ether extract) content. The abdominal fat was excised as well. Based on the results of dissection, the dressing percentage and the share of muscles and abdominal fat in chilled carcass were established. All the experimental data underwent two-way analysis of variance.

Results

The body weight of control and experimental broilers aged 42 and 47 days at slaughter was similar, respectively 2529 and 2506 g, though this parameter could not affect investigated characteristics, given in the tables below.

Tab. 1. Carcass characteristics and chemical composition of breast and thigh muscle (%)

Group	Chilled carcass			Breast muscle		Thigh muscle
	Dressing percent.	Share of muscles	Share of abd. fat	Crude protein	Ether extract	Crude protein	Ether extract
C	78.4^a	42.5^a	1.48^a	23.25^a	0.97^a	18.82^a	5.51^a
±	1.61	4.10	0.40	0.22	0.03	0.23	0.33
E	77.3^a	42.8^a	1,55^a	23.44^a	0.72^b	19.08^b	4.60^b
±	1.80	3.04	0.46	0.27	0.04	0.26	0.29

a,b… means with different superscripts in columns differ significantly at p ≥ 0.05

Tab. 2. Sensory evaluation of poultry meat (points)

Group	Breast				Thigh
	Odour	Tender-ness	Juici- ness	Total	Odour	Tender-ness	Juici- ness	Total
C	4.45^a	4.57^a	4.49^a	4.51^a	4.62^a	4.71^a	4.69^a	4.71^a
±	0.07	0.03	0.09	0.05	0.03	0.03	0.09	0.06
E	4.49^a	4.62^a	4.61^a	4.57^a	4.68^a	4.69^a	4.72^a	4.69^a
±	0.06	0.04	0.11	0.10	0.04	0.07	0.04	0.04

Conclusion

Feeding broiler chickens growing and finishing complete feeds with lowered energy level has no significant effect on carcass characteristics and sensory evaluation of meat. On contrary, it increases the content of crude protein in the breast (slightly) and thigh muscles, and decreases the concentration of intramuscular fat.

arski