Abstract
Before slaughter, broilers are subjected to several preslaughter management events such as feed withdrawal, catching, crating, transport, and lairage. The aim of this study was to gain insight into factors which influence mortality, stress, energy metabolism, and meat quality of the broilers on the last day of their life.
The
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mean percentage of broilers that arrived dead at the conveyer belt of the slaughterhouse (DOA) was 0.46. Factors associated with DOA percentage were ambient temperature, moment of transport, catching company, breed, flock size, mean body weight, mean compartment stocking density, transport time, lairage time, and the interaction term transport time x ambient temperature. The most important factors that influence DOA percentage, and which could be reduced relatively easily, were compartment stocking density (Odds Ratio (OR) = 1.09 for each additional bird in a compartment), transport time (OR = 1.06 for each additional 15 min), and lairage time (OR = 1.03 for each additional 15 min).
Moreover, the mean percentage of bruises was 2.20. Factors associated with corrected bruises percentage were season, moment of transport, and ambient temperature.
To establish predisposing factors for DOA broilers a gross post mortem investigation was done. Macroscopic lesions were found in 89.4% of DOA broilers. Signs of infectious diseases appeared to be most frequent (64.9%), followed by heart and circulation disorders (42.4%), and trauma (29.5%). The right ventricle mass to the total ventricle mass (RV:TV) was significantly higher in DOA broilers than in slaughtered broilers.
Manual catching of broilers leads to stress in the birds and is backbreaking for the workers. Therefore, mechanical catching of broilers was investigated. Mechanical catching was associated with higher DOA percentages than manual catching. However, the catching method did not influence the percentages of bruises, meat quality, and corticosterone (CORT) levels.
Feed is normally withdrawn for several hours before catching in order to reduce the danger of carcass contamination. Feed withdrawn broilers showed higher thyroxine and lower triiodothyronine, triglyceride, glucose, and lactate concentrations compared to broilers that had access to feed before the transport intervention. These findings indicate a negative energy balance, and, accordingly, BW losses occurred. BW losses further increase during transport.
To reduce the negative effects of feed withdrawal semisynthetic diets were investigated. After transport the BW loss of broilers fed semisynthetic diets was 0.24% / h less than of feed withdrawn broilers. BW loss of broilers fed conventional diets was 0.28% / h less than of feed withdrawn broilers. Moreover, the digestive tract mass was lower in broilers fed a semisynthetic diet than in broilers fed a conventional diet, which can lead to a lesser degree of contamination during evisceration. Beside that, no increase of CORT was found due to transport in broilers fed a semisynthetic diet, whereas CORT significantly increased during this period in broilers fed a conventional diet. Consequently, semisynthetic feed is a promising alternative for feed withdrawal in the period before catching and crating.
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