Role of Early Incubation Temperature Variation in the Development of the Wooden Breast Myopathy in Broiler Chickens

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Source: US Poultry & Egg Association

Institution: Auburn University

Principal Investigator: Jessica D. Starkey, Ph.D.
Auburn University
Department of Poultry Science
201 Poultry Science Building
Auburn, AL 36849

Multi-stage egg incubation systems are challenging to manage and attempts to keep late-stage embryos from overheating create situations where early-stage embryos are at sub-optimal temperatures during the period when skeletal muscle fiber number and satellite (muscle stem) cell populations are being established (embryonic day (ED) 4 to 11). There is little published evidence regarding the impact of variation in early-stage (ED 4 to 11) incubation temperature on modern broiler embryonic skeletal muscle development and post-hatch muscle growth characteristics, feed efficiency, meat yield or incidence of myopathies in modern commercial broilers. The project objectives were established to provide information currently unavailable in the scientific literature for use by industry professionals in optimizing incubation methods and operational parameters to maximize hatchability, chick quality, growth performance and meat yield, as well as to determine the impact on the incidence and severity of the breast meat quality defects, wooden breast and white striping, in modern commercial broiler chickens.

The project objectives were to determine the impact of early-stage (embryonic day (ED) 4 to 11) incubator temperature variation (36.1°C = COLD vs. 37.1°C = Control (CTL) vs. 38.6°C = HOT) on commercial broiler chicken growth performance and feed efficiency, carcass and breast meat yield, and the incidence and severity of meat quality defects, such as wooden breast and white striping, as well as skeletal muscle developmental characteristics, satellite cell (SC; muscle stem cell) mitotic (proliferative) activity, and muscle growth characteristics at multiple time points over the rearing period.

Hatch Characteristics: Early-stage incubation temperature treatments did not alter embryonic mortality (early, middle, late and total dead; pipped; malpositioned), egg weight loss during incubation, nor the proportion of male and female chicks at hatch. Hatch of fertile tended to be lower in eggs incubated in both the COLD and HOT incubators compared with those in the CTL incubators. Since chicks were removed from the hatchers simultaneously to facilitate vent sexing. As expected, chicks hatched from the COLD treatment incubators were heaviest at hatch, while those from the HOT treatment were 10% lighter. The CTL chicks were intermediate.

Growth Performance: Incubating broiler hatching eggs at air temperatures of 36.1°C (COLD) during early-stage incubation (ED 4 to 11) negatively impacted broiler day 0 to 32 body weight gain and final body weight compared with the CTL (37.1°C) treatment. Incubating eggs at 38.6°C (HOT) during early-stage incubation resulted in similar performance metrics when compared with those incubated at the CTL temperature of 37.1°C from ED 4 to 11.

Carcass Characteristics: Incubating broiler hatching eggs at 36.4°C (COLD) during early-stage incubation (ED 4 to 11) negatively impacted breast, wing, thigh and drum chilled parts weights and breast yield compared with those incubated at the CTL (37.5°C) temperature. Birds from the COLD incubators tended to have a 25-g reduction in breast weight (412 vs. 438 and 443 g) that resulted in a 6% decrease in breast meat yield compared with those from CON and HOT incubators. Incubating eggs at 38.6°C (HOT) during early-stage incubation resulted in reductions in wing and drum chilled parts weights but did not impact breast, tender and thigh weights compared with birds from the CTL incubators. Altering early-stage incubation temperature did not impact the incidence nor severity of wooden breast or white striping meat quality defects in broilers reared to 32 days-of-age.

Satellite Cell Activity and Muscle Growth Characteristics: Altering the early-stage incubation temperature from ED 4 to 11 did not influence the proliferative activity or myogenic regulatory factor expression profiles of breast muscle satellite cells on day 7, 14, 21 or 28 post-hatch. However, the cross-sectional area of breast muscle fibers of birds from the CTL and HOT incubation treatments was larger on both day 7 and 21 post-hatch compared with those from the COLD incubators. These results help explain the 6% lower breast meat yield observed in birds from the COLD vs. HOT and CTL treatments.

Overall, the results of this project highlight the importance of careful hatching egg incubator management. These results indicate that the cost of incubating broiler hatching eggs at sub-optimal temperatures (36.4°) during early-stage incubation can be as much as 25 grams per bird, which if breast meat is worth $0.438 per gram [USDA 3-year average 199 cents per pound (range 150 to 248)], that is an estimated $7.1 million dollars per year in a typical 1.25-million-broilers-per-week integrated commercial broiler complex or $854.7 million dollars per year for the U.S. broiler industry as a whole.