Transport of 18-day old hatching eggs - effects on physiology and behaviour in broiler chicken

Incubation and hatching commonly takes places at hatcheries, separate from the grow-out facilities where broiler chicks are raised. This means that chicks are sorted and transported immediately after hatch, during which time they typically do not have access to feed and water, and are subjected to transport stress. Depending upon hatch and transport time, feed and water deprivation can be up to 72 hours post-hatch. Recently, innovative housing systems are being developed in which fertilized eggs are transported on embryonic day 18 from the breeding to the grow-out facility, where they hatch on day 21. In chicken, the hypothalamic–pituitary–adrenal (HPA)-axis becomes functional around embryonic day 14-16. It is therefore conceivable that transport of eggs may lead to a stress response. Exposure to prenatal stress may affect the coping capacity of the individual and negatively impact its further development. This may have practical implications for transportation of embryos in ovo. We investigated whether prolonged transport on embryonic day 18 has effects on the development of a slow growing broiler chicken strain (Hubbard JA257). E18 eggs (n=90) were transported for either 41 minutes (short transport, ST, n=45) or 219 minutes (long transport, LT n=45). Before, during and after the transportation, heart rate (bpm) was recorded using four digital egg monitors (Buddy™, Vetronic Services, UK) in 12 ST eggs and 12 LT eggs. Heart rate was recorded immediately prior to departure from the breeding facility (HR 0) and immediately upon arrival at the research facility (HR1) after 41 minutes. HR in the LT embyos was recorded again at 120 minutes of transport (HR3) and 219 minutes of transport (HR4). Transportation significantly increased embryonic heart rate from 130,87±2,82 at HR0, to 144,45±2,77 at HR1, 159,44±3,79 at HR 3, and 157,50±3,90 at HR4 (F1,3 =15.8, p < 0.001) . This increase continued during an intermediate measure at 120 minutes. The increased embryonic HR then remained high at measurement immediately following LT. We did not find effects of prolonged transport on behavioural parameters measured in the juvenile chicken (n= for ST and n=12 for LT) in the tonic immobility (conducted at 3-4 days of age; n=41 ST and n=41 LT) and open field test (measured twice, on 9-11 and 35-37 days of age; n=45 ST and n=45 LT). Concentrations of feather corticosterone as measured in primary flight feather 2 did not differ on postnatal day 36 (n=45 ST and n=44 LT). We showed that transport leads to an autonomic stress response in 18-day old chicken embryos, but that this elevation had no further effects on other indicators of prenatal stress. Nevertheless, our results emphasize that also transport of incubated eggs should be as refined as possible to minimize the exposure to stress.