Effects of Incubation Humidity and Hatching Time on Heat Tolerance of Neonatal Chicks: Growth Performance After Heat Exposure

Abstract

Three experiments were performed with 300 neonatal Hisex Brown layer chicks in each. The chicks hatched from eggs incubated at a relative humidity (RH) of 55 or 45%. Within each RH group, two groups were separated based on hatching time (early and late hatch groups). After hatch, 60 chicks served as controls. The other chicks were exposed to 35, 37, or 39 C for 48 h. After exposure, a 4-wk experimental growing period started at Day 2 of age. Chicks exposed to the experimental temperature regimens for 2 days had lower body weights at the end of exposure and grew less than controls during the 1st wk afterwards. At Day 2 of age, chicks hatched from eggs incubated at 45% RH had higher body weights than chicks hatched from eggs incubated at 55% RH. These chicks also had higher body weight gain in the 1st and 2nd wk following exposure to 39 C than chicks hatched from eggs incubated at 55% RH. Chicks hatching late were heavier at Day 2 than early-hatching ones, but body weight gain was similar. Chicks exposed to the experimental temperature regimens had lower rectal temperatures than controls at the end of the 1st and 2nd wk. Incubation RH, hatching time, and sex did not affect feed intake, feed conversion, or rectal temperature. After exposure to 39 C, fewer chicks that had hatched from eggs incubated at low RH died compared with chicks that had hatched from the 55% RH group. Early-hatching chicks had a significantly higher risk of dying than late-hatching ones.

Effect of Hatching Time on Yolk Sac Percentage and Broiler Live Performance

“…Mortality was not affected by hatch time in the previous studies (Blake et al, 2013;Dişa et al, 2015). In some previous studies extended holding in the hatcher increased early rearing mortality (Hamdy et al, 1991;Pinchasov & Noy, 1993). On the contrary, Early hatched chicks exhibited lower mortality even when their holding period was longer than late hatched chicks in the present study.…”

“…Thus, early hatching chicks have generally remained in the hatcher longer while awaiting removal of later hatching chicks from the machine (pull time) (Elibol et al, 2011;Powell et al, 2016). It has been reported that performance after placement was negatively associated with the time that chicks remained in the hatcher after hatching (Decuypere et al, 2001;Halevy et al, 2003) or that delayed access to feed depressed growth after access to feed (Careghi et al, 2005), and increased mortality (Hamdy et al, 1991). El Sabry et al (2013) reported that early hatching chicks were not able to compensate for their post hatch BW loss and weighed less at 35 d of age.…”

Research Note: Interaction between hatching time and chick pull time affects broiler live performance

“…Some previous studies have shown that chicks remaining in hatchers longer became dehydrated and exhibited increased early rearing mortality compared with those removed soon after hatching ( Hamdy et al., 1991 ; Pinchasov and Noy, 1993 ). Furthermore, Vieira and Moran (1999) showed that 24-h delays in housing increased total mortality, primarily due to inaccessibility of feed and water, resulting in dehydration and a shortage of available energy.…”

Rectal temperature as an indicator for heat tolerance in chickens

“…Both RT and DTn have been suggested as indicators for the assessment of the performance of chickens in different species, strains or populations under heat stress (Sykes & Salih 1986;Hamdy & Henken 1991;Eberhart & Washburn 1993;Abu-Dieyeh 2006;Chepete 2008). However, hens exposed to heat stress longer than 30 h would suffer irreversible damage.…”