Abstract. This study aimed to determine the changes in the performance, welfare, and productivity level of broiler chickens reared at various group sizes (GS3000, GS4000, GS6000, and GS20 000) under intensive field conditions. The study was carried out according to a randomized block design with four different group sizes (GS) in three trials. Weekly body weights (BWs) were determined randomly in 150 individuals from each GS group. Feed intake (FI), feed conversion ratio (FCR), and European production efficiency factor (EPEF) were determined for each GS treatment. Body defects (footpad dermatitis, FPD, hock burn, HB, and the breast burn, BB) were measured randomly in 150 chickens (75 male and 75 female) from each group using a visual scoring system with a 0–3 scale. At 1 and 2 weeks of age, GS3000 broilers had similar BW to GS6000 and higher than GS4000 and GS20 000. However, this situation changed at 6 weeks of age and the male chickens in GS6000 became heavier than in GS3000, GS4000 and GS20 000 (P = 0.007). No differences in mean values of temperature, humidity, air velocity and litter moisture levels were observed among GS treatments. GS3000 and GS4000 chickens had significantly lower levels of FPD, HB, and BB than chickens reared in GS6000 and GS20 000 (P < 0.001). The EPEF values from highest to lowest were 425.8, 404.5, 358.8, and 354.0 in the GS6000 GS3000, GS4000, and GS20 000 groups, respectively. In conclusion, our study results showed that rearing in groups of 6000 broilers had both better performance and higher overall productivity than other groups but tended to show more severe body defects.

This study aimed to determine the changes in the performance, welfare, and productivity level of broiler chickens reared at various group sizes and non-grouped (single flock) under intensive field conditions. Two treatments were tested as a concept in all trials. In the GF (grouped flock) house, the grouping was applied at 6000 (GF 1 or large GF), 4000 (GF 2 or medium GF), and 3000 (GF 3 or small GF) broilers in the first, second and third trials, respectively, without changing the stocking density. In the SF (single flock) house, classical intensive rearing was applied without grouping the whole 20000 broilers during each of 3 trials (SF 1, 2, and 3). The results showed that large and medium GF chickens had higher BW than SFs at slaughter age. In SF 2 chickens, only HB level was significantly higher in the second trial (1.39 vs. 1.17). In the third trial, the FPD, HB, and BB scores of SF 3 chickens were higher when compared to small GFs at 1.85 to 1.41, 1.48 to 1.22, and 2.27 to 1.89, respectively. Chickens reared in GFs had more BW, FI, and better FCR and EPEF values when compared to SF chickens. BW, FI, and EPEF were observed to be lower—while FCR was higher—when SF chickens were compared to GFs. Upon considering the EPEF value along with welfare parameters, it has been observed that rearing chickens in groups of 3000 may increase productivity by up to 54.8% according to intensive conditions.