Investigation of the effects of growht rate on performance and meat quality defects in broiler hybrids

In current research, the effects of different growth rates on performance, breast meat quality, morphometric structure of breast muscle, biochemical properties, histology of breast muscle and white strip abnormalities in broiler hybrids were investigated. The experimental groups were as Group 1: Ross 308 (ad libitum; AL-R); Group 2: Cobb 500 (ad libitum; AL-C); Group 3: Hubbard Red JA (ad libitum; H); Group 4: Ross 308 (pair-fed; PF-R) and Group 5: Cobb 500 (pair-fed; PF-C). There were 5 repetitions in each group and 12 chickens in each repetition (300 in total). Group 4 and 5 were fed as much as the daily amount of feed consumed by group 3 (pair-fed). Group 1 and 2 were slaughtered on 49th day of experiment, and group 4 and 5 (pair-fed groups) were slaughtered when they reached the slaughter weight of day 49 of their genotype. For the analysis, 15 chickens showing the average weight from each group were slaughtered and samples were collected under appropriate conditions. On the 48th day of study, the highest body weight was found in AL-R genotype, followed by AL-C and H groups, respectively. The body weight was determined similar in PF-R and PF-C groups, body weight was lower in H group compared tho these groups (P<0.001). In the ad libitum fed groups, the highest feed intake was AL-R, AL-C and H between the 7th and 48th days, respectively (P<0.001). Since PF-R, PF-C groups are fed similarly to H group, feed consumption is also similar (P>0.05). The feed conversions ratio were similar in groups AL-R, AL-C, PF-R and PF-C, and better than group H on days 7-48 (P<0.001). Body weight gains on days 7-56 and 7-63 were low in the H genotype (P<0.001). In these periods, the feed efficiency value was numerically high in the H genotype (P<0.001). Compared with the ad libitum groups, in the pair-fed groups, breast percentage decreased (P<0.001) and thigh percentage increased (P<0.01). In the pair-fed groups, pectoral muscle length increased (P<0.001), width (P<0.001) and depth (P<0.01) decreased. The white stripe value was higher in AL-R than in PF-R (P<0.05) and in AL-C compared with PF-C (P<0.001). Serum creatine kinase (CK) and lactate dehydrogenase (LDH) were low in the pair-fed groups (P<0.001). Breast meat protein content was statistically similar between groups, whereas fat content was higher in AL-R than in PF-R (P<0.01). Fibrosis (P<0.01), mononuclear cell infiltration (P<0.001), degeneration (P<0.01), and lipidosis (P<0.01) were higher in the AL-R group than in the PF-R group. The infiltration level was higher in the AL-C group than in the PF-C group (P<0.05). A significant correlation was found between white line score and slaughter weight, carcass weight, breast weight, width, and depth of the pectoral muscle (P<0.05). As a result, the rate of white strip defect decreased with slowing growth rate. With the slowing growth, the morphometric structure of breast muscle changed, the levels of CK and LDH, which are indicatörs of muscle damage, decreased. In addition, the deterioration observed at the cellular level was reduced and physicochemical quality of the breast meat has increased.