Incubation temperature manipulation during fetal development reduces adiposity of broiler hatchlings

Broilers are known as an efficient source of lean meat. Genetic selection resulted in broiler strains with large body size and fast growth, but a concomitant increase in fat deposition also occurred. Other than reducing nutrient intake, there is a lack of alternative methods to control body fat composition of broilers. The present study assessed whether incubation temperature (machine temperatures: 36 degrees C, 37.5 degrees C, and 39 degrees C; eggshell temperatures: 37.4 +/- 0.08 degrees C, 37.8 +/- 0.15 degrees C, and 38.8 +/- 0.33 degrees C, respectively.) from d 13 affects broiler hatchling fat deposition. We analyzed adipocyte hypertrophy and proliferation in 3 body regions; weight and chemical composition of yolk-free chicks and yolk sacs; and serum lipid profile. Increased incubation temperature reduced abdominal and cervical adipocyte size. Independently of temperature, cervical adipocytes were smaller and showed higher proliferation than adipocytes in the abdominal and thigh regions. Smaller cervical adipocytes were observed in birds from eggs incubated at 36 degrees C and 39 degrees C. With regard to weight and composition of chicks, ash content as a percentage of dry matter was the only variable affected by temperature; it was higher in chicks from eggs incubated at 36 degrees C than at 39 degrees C and showed no significant difference between chicks incubated at 39 degrees C and 37.5 degrees C. Absolute and relative weights of yolk sacs were higher from eggs incubated at 39 degrees C than at 36 degrees C, and these two treatments did not differ from the 37.5 degrees C control. Absolute measures of yolk sac lipids, moisture, dry matter, and crude protein content were lower in chicks from eggs incubated at 36 degrees C, and no significant differences were found for these variables between chicks from eggs incubated at 37.5 degrees C and 39 degrees C. Hatchlings from eggs incubated at 36 degrees C had significantly higher cholesterol levels than chicks incubated at the other 2 temperatures, but no additional effects on blood lipids were detected. Incubation temperature manipulation during fetal development altered cervical and abdominal adipocyte size in broiler hatchlings and could become a tool in hatcheries to manipulate chick quality, although further studies are needed to evaluate its long-term effects.