Effects of dietary nutrient concentrations on performance, carcass and meat quality traits of organically reared barred plymouth rock chickens

The study aimed to assess the performance, carcass traits, chemical and amino acids (AA) composition of breast and thigh meat organically reared Barred Plymouth Rock (BPR) chickens fed different nutrient concentrations. A total of 240 one-day-old BPR mixed-sex chicks (average weight 35.57 +/- 0.17 g) were allocated in a complete randomized design into 3 dietary treatments with 8 replicates of 10 chicks each, and used in an 84-d feeding trial according to organic meat technology (Regulations 834/2007 and 848/2018). Dietary treatments consisted of a basal isocaloric and isonitrogenous organic diet as a control (T0), isocaloric and low-crude protein (CP) level organic diet (T1; 1% CP lower) and isonitrogenous and low-metabolizable energy (ME) level organic diet (T2; 220 kcal/kg ME lower). Results showed that dietary treatments did not influence the overall weight gain of BPR chicks, but feed conversion ratio was poorer in experimental (T1 and T2) diets than in control. There were no effects of dietary treatments on carcass traits and digestive organs. Proximate composition (dry matter, fat, protein, ash) and energy value of meat were not altered by treatments, except the protein content of thigh muscle significantly decreased in T1 compared to the other treatments. Certain individual AA, which included phenylalanine in breast muscle, as well as lysine and phenylalanine in the thigh muscle, decreased by fed T1 diet, leading to a significant decrease in both breast and thigh muscles of total AA (TAA) and essential AA (EAA) in T1 than the other treatments. The non-essential AA (NEAA) and the ratios of EAA/TAA or EAA/NEAA did not differ among treatments. Our results show that irrespective of dietary treatments or muscle type, the meat of BPR chicks has a balanced AA profile with more than 40% EAA/TAA ratio and more than 60% EAA/NEAA ratio. In conclusion, these findings indicate that fed low-energy diet (2770 kcal/kg ME and 21.4% CP in starter-grower phase, respectively 2880 kcal/kg ME and 18.6% CP in finisher phase) in BPR chicks represents an alternative with no adverse effect on productive performance, carcass traits, and meat protein quality.