(Summary by Nancy Fischer of the University of Saskatchewan of papers presented
at the 1997 annual meeting of the Poultry Science Association)
Some recent research conducted at North Carolina State University on the effects
of longer-than-usual egg storage on hatchability was presented at the annual meeting
of the Poultry Science Association at the University of Georgia
One of the papers, presented by Dr. G. Fasenko, now a researcher at the University
of Alberta, highlighted the differences in incubation times for turkey eggs
stored for either 4 or 14 days. The eggs that were stored longer before setting
ended up taking from 12 to 18 hours more time in the incubator before hatching.
The fertility and hatchability of fertile eggs from each storage time was also
evaluated (Table 1). Fertility, as expected, was not influenced by storage time
but hatchability was significantly lower for 14d stored eggs.
Egg Storage time
The researchers studied some of the reasons for this increase by breaking down
the added time in the incubator into hours until internal pipping, when the hatching
bird breaks through the shell membrane, and external pipping, when the bird breaks
through the shell itself. They found that the time interval between internal and
external pipping was around 7 hours longer for poults from eggs stored for 14
days before setting. These results led the researchers to question the hardiness
of the chicks from 14d stored eggs.
When the hatched poults were assessed for their relative nutrient status, it was
found that the poults from the stored eggs have to rely on energy-costly metabolic
glucose synthesis from body fat and amino acids (gluconeogenesis) for survival.
Poults from eggs not stored as long relied, instead, on the breakdown of stored
carbohydrate (liver glycogen) to meet their post-hatch energy requirements.
Broiler Breeder Eggs
Two additional papers were presented on the effects of egg storage time on
some broiler chick embryo growth parameters. Dr. V. Christensen of North Carolina
State explained that some strains of broilers seemed resistant to the negative
effects of longer term egg storage on embryo survival and therefore on hatchability.
In looking for an explanation for this strain difference, he studied organ development
of embryos to determine whether the organs that either supplied the stored energy
(liver) or the organs that required the energy for hatching (heart and pipping
muscle) grew at different rates in the different strains of birds and with different
egg storage times. His research results showed that storing eggs for 14 days
prior to setting slowed the growth of all organs evaluated in both genetic lines
of birds. He noted that no one organ in the bird appeared to be more influenced
by egg storage than any other.
Looking even more closely at the physiological reasons for these genetic differences,
the researchers ended up suggesting that the genetic lines that had better embryo
survival after longer term egg storage were able to metabolize and store more
adequate amounts of carbohydrate in the tissues where it was needed than the
genetic lines with poorer hatchability after egg storage.
These types of research findings have led to other researchers attempting to
improve post-hatch survival rates by providing birds with readily available
energy sources to supplement depleted yolk sac reserves. A paper presented by
S.I. Vieira of Auburn University summarized an experiment where either corn
alone or a starter diet supplemented with calcium propionate was fed to broiler
chicks for the first four days post-hatch. In this study, both treatments were
successful in reducing early mortality; however, both also caused significant
reductions in performance. The performance decreases, when the calcium propionate
was fed, were not carried through to 49 days of age. The researchers concluded
that although propionate did reduce early mortality, some of the proteins broken
down for energy use during gluconeogenesis may have reduced muscle development
in the young bird.
Follow-up work on hatchability and embryo growth in broiler eggs has since been
conducted by Dr. Fasenko at the University of Alberta, and has shown an average
10-hour increase in time to internal pipping, external pipping and hatch in 14d
versus 4d stored eggs. Preliminary research results indicate that both the onset
and rate of embryo growth are slower in 14d stored eggs. This project is ongoing
and will evaluate the effects of egg storage time on the post-hatch development
of broiler chicks.