M. Oblakova1, N. Mincheva1, P. Hristakieva1, I. Ivanova1, M. Lalev1, Sv. Georgieva2

1Agricultural Institute – Stara Zagora, 6000, Bulgaria
2Department of Genetic, Breeding and Reproduction, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria

(Manuscript received 3 July 2017; accepted for publication 5 October 2017)

Abstract. The experiment was conducted in the breeder farm of department Population genetics, reproduction and technologies of poultry and rabbits at the Agriculture Institute of Stara Zagora. Five lines from the National Gene Pool of Bulgaria: line Ss (Sussex), line E (Barred Plymouth Rock), line NG (New Hampshire), line F (NG x Red Rhode Island), line L (White Plymouth Rock) were used as maternal forms in the crossing schedule and line M (Cornish) as a paternal form for production of slow-growing broilers. The birds were grown to 84 days. Feeding was done with compound feeds according to the age: starter (1/14 days of age), grower (14/28 days of age), finisher (28/84 days of age). By the end of the experiment, slaughter analysis was performed with 3 female and 3 male broiler chickens per group with live weight corresponding to the average of each genotype. The live weight was determined, as well as the grill weight, the weights of cuts (breast, thighs, wings), edible offal (heart, liver, gizzard) and abdominal fat. On the basis of these data, the slaughter yield and body parts ratios were calculated. The data for the live body weights of birds at slaughtering indicated the highest values for group V – 4040g, followed by groups ІV and ІІ – 3271.67g and 3186.67g, respectively (p<0.05). There was a statistically significant difference between the sexes with superiority of male birds (p<0.001). In the other 3 groups, breast meat percentage ranged from 19.48 to 19.84%. The share of thighs from the grill was the greatest in slow-growing chickens from group II – 33.01%, followed by group І – 32.35%, group IV – 32.18%, and the lowest- in groups ІІІ and V (31.91% and 31.18%, respectively). The analysis of data exhibited a significant effect of the genotype on water content of breast meat (resp. Dry matter), with lower values in slow-growing birds from group III – 73.19% (p<0.05), whereas in the other groups it ranged between 73.44 and 73.62%. The dry matter higher percentage was associated with better lavor of meat. The analysis of the effect of genotype on meat protein content showed that protein content was the highest in the breast of slow-growing chickens from group III- 24.89% and lowest in the breast meat of conventional broilers from group V – 23.86% (p<0.05). In the other 3 groups, it ranged from 24.55 to 24.59%. The protein content of thighs was the lowest in slow-growing birds from group I- 19.49%, and the difference was the highest when compared to groups II and III, also slow-growing (p<0.05). With respect to the thigh fat content, it was the highest in slow-growing chickens from group IV (5.84%), followed by fast-growing from group V (5.33%) and the lowest- in slow-growing birds from group І – 4.12% (p<0.05). The analysis of data showed a statistically significant effect of the sex on water content (p<0.001), fat (p<0.001) and ash (p<0.01). In males, thigh meat contained water and ash and in females more fat. The interaction of genotype and sex effects were important for thigh meat fat content, with highest values in fast-growing females from group V – 5.98% and lowest in slowly growing males from group I – 3.88% (p<0.001). Weak but statistically significant interaction between both factors was found with respect to thigh protein and ash (p<0.05). The highest protein content was established in slow-growing females from group IV (19.81%), whereas thigh ash was with highest percentage in slow-growing males from group II (1.11%).