Influence of increasing slaughter age of chickens on meat quality, welfare, and technical and economic results

Because of the increasing demand for rawcuts and processed products, there is a trend to producingvery heavy broilers. Breeds that are used for such kinds ofproduction have been intensively selected for growth rateand breast meat yield, and birds are reared for a longerperiod than standard broilers. This study was to evaluatethe effects of increasing slaughter age on technical andeconomic factors, including production effi ciency andenvironmental costs, bird welfare, and breast meat qualityin a modern heavy broiler line. Five groups of 300 maleRoss 708 chickens were reared until slaughter ages of 35,42, 49, 56, or 63 d. Increasing age at slaughter from 35to 63 d resulted in a 7.4-fold increase (P < 0.01) in mortalityrate (5.21 vs. 0.70%). It also increased (P < 0.001)the slaughter weight and ADFI of birds 2.5- and 1.4-fold,respectively, without affecting their G:F. Under our experimentalconditions, economic profi t evaluated through thenet gain reached a maximum at 42 d. The moisture andammonium content of litter increased (P < 0.05 and P <0.01, respectively) rapidly during rearing concomitantlywith increased (P < 0.05) occurrence and severity of contactdermatitis and decreased (P < 0.05) walking abilityand activity of birds. Thermal comfort also decreased (P< 0.05) greatly as early as 42 d of age. Changes in carcassquality occurred mainly between 35 and 56 d of age, witha progressive increase (P < 0.001) in breast and leg yield,whereas body fatness was barely affected by age. Majorchanges in breast meat traits were observed between 35and 49 d of age, with an increase in muscle pH at 15 min(P < 0.01) and 24 h (P < 0.001) postmortem and reduced(P < 0.001) lightness and drip loss. The protein and lipidcontent of raw breast meat also increased (P < 0.05 and P <0.01, respectively) with age. Taking into account the mainaspects of sustainability, we could recommend slaughteringchickens of heavy line at 42 d of age.