Previous studies conducted on meat-type chickens in the laboratory of the Institute of Animal Science in Israel showed that thermal manipulation of the embryo during the time window of the hypothalamus–hypophysis–thyroid axis development and maturation significantly reduced the metabolic rates of the embryo and the chicken, improving the post-hatch feed conversion rate, report Yogev Piestun and co-authors there and at the University of Jerusalem.

The aim of their latest study, published in Poultry Science, was to investigate the effect of intermittent thermal manipulation during turkey embryogenesis on embryo development.

Fertile turkey eggs were divided into three treatments:

• control
• 6H – with thermal manipulation by elevation of temperature and RH by 1.7°C and nine per cent, respectively, above the control conditions for six hours per day, from days 10 to 22 of incubation, i.e. 240 to 552 hours of incubation and
• 12H – with thermal manipulation as above, for 12 hours per day, during the same time period.

From days 0 to 10 and from day 23 onwards, all eggs were incubated under control conditions.

The embryo growth rate was not negatively affected by thermal manipulation.

During thermal manipulation, eggshell temperature, the embryonic heart rate and oxygen consumption were elevated by the manipulation while the embryos were in their ectothermic phase. However, by the end of the thermal manipulation period and until hatch (the endothermic phase), these parameters were significantly lower in both thermal manipulation treatments than in the control, indicating a lower metabolic rate and heat production.

The thermally manipulated embryos hatched approximately 10 hours earlier than the controls, without any negative effects on chick bodyweight or hatchability.

However, thermal manipulation treatments resulted in a higher proportion of chicks with unhealed navels.

Body temperature at hatch was significantly lower in the thermally-manipulated chicks than in the controls, suggesting lower heat production and metabolic rate, which might affect the energy requirements for post-hatch maintenance.

Piestun and co-authors concluded that thermal manipulation during turkey embryogenesis might have altered the thermoregulatory set point, and thus lowered the embryo metabolic rate, which might have long-lasting effects post-hatch.

Reference

Piestun Y., I. Zimmerman and S. Yahav. 2015. Thermal manipulations of turkey embryos: The effect on thermoregulation and development during embryogenesis. Poultry Science. 94: 273-280.
doi: 10.3382/ps/peu047

March 2015