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

Chantier qualité GA

English. 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.