Previous studies have shown that relative humidity during incubation of chicken eggs influences water loss from the egg and embryonic mortality, according to C.W. van der Pol of HatchTech in the Netherlands and co-authors there and at Wageningen University.

In those studies, eggshell temperatures were not monitored or controlled. Because relative humidity influences the egg’s heat loss through evaporation, eggshell temperatures might have been different between relative humidity treatments, influencing embryonic mortality and development.

To eliminate the effect of eggshell temperatures, van der Pohl and co-authors report in Poultry Science their latest experiments, in which eggs were incubated at an eggshell temperatures of 37.8°C from embryonic day (E) zero until E18 and at a high (55 to 60 per cent) or low (30 to 35 per cent) relative humidity from E2 until hatch.

Embryonic mortality, hatch curve and several chick quality characteristics (length, weight, navel quality, organ weights and dry matter of the yolk-free body mass and yolk) were determined on E18 and at hatch.

Low relative humidity increased egg weight loss between E0 and E18 (+3.0 per cent) and third week embryonic mortality (+3.0 per cent of fertile eggs) and decreased hatch of fertile eggs (−2.9 per cent of fertile eggs) compared with high relative humidity.

Hatch duration and chick quality characteristics did not differ between relative humidity treatments.

To assess the effect of relative humidity during incubation on post-hatch performance under sub-optimal conditions, hatchlings were brooded at a normal (35.0°C at day 0, decreasing to 27.0°C at day 4) or cold (27.8°C at day 0, decreasing to 25.6°C at day 4) temperature until four days post-hatch.

Incubation relative humidity and brooding temperature significantly interacted with post-hatch growth but not development. Both low and high relative humidity × cold brooding temperature resulted in lower (−6.9 and −6.0 g, respectively) bodyweight than high relative humidity × normal brooding temperature at four days of age of age.

The cold brooding temperature resulted in lower daily feed intake (−1.3g per chick) than the normal brooding temperature.

Incubating eggs at a low relative humidity compared with a high relative humidity and maintaining the eggshell temperatures at 37.8°C decreased hatch of fertile eggs, concluded van der Pohl and co-authors, but it had little effect on chick quality or post-hatch performance.

Reference

^{Van der Pol C.W., I.A.M. van Roovert-Reijrink, C.M. Maatjens, H. van den Brand and R. Molenaar. 2013. Effect of relative humidity during incubation at a set eggshell temperature and brooding temperature posthatch on embryonic mortality and chick quality. Poult. Sci. 92(8):2145-2155. doi: 10.3382/ps.2013-03006}

September 2013