Successful incubation, and the production of high quality chicks, require that hatchery managers be observant and willing to fine tune their machines. Embryos must be allowed to develop properly, and are reliant on the hatchery manager understanding embryonic development, adapting incubation parameters, and understanding how the embryo is influenced by the egg shell properties, and the nutrients the eggs contain.
Hatchery managers must provide an environment that helps the developing embryo to utilize an egg’s nutrients. These nutrients include the proteins (amino acids), and carbohydrates predominately associated with the albumen, lipids (fatty acids) and trace minerals predominately associated with the yolk, and macro minerals associated with the shell. Equally important is water movement within the egg, and how the diffusion of gases through the shell is influenced by the egg shell properties, the incubator and hatchery room management.
Nutrients, which are utilized by the embryo through the developing extra-embryonic components, include the amnion, chorio-allantoic membrane, and the yolk sac, which are extra-embryonic membranes, and the formation of sub-embryonic fluid. If any of these components fails to properly develop there is reduced nutrient utilization and lower hatchling quality.
The shell supplies nutrients, but also influences how other nutrients are utilized through what we term “shell properties.” The shell properties influence the ability of water vapor, oxygen and carbon dioxide, as gases, to pass through the pores to, and from, the developing embryo.
The shell properties are also modified by how hatchery personnel manage the environmental humidity, ventilation of the hatchery rooms and incubators and pressures within the incubators and hatchery rooms, because gases can only pass through the shell by passive diffusion, i.e. from an area of high to an area of low concentration.
Temperature regulation is the most important parameter influencing the embryos’ growth in the incubator, although humidity regulation, ventilation (both air composition and flow across the eggs) and turning are also critical.
During the initial incubation stages, the young, developing embryos must have sufficient heat to allow for proper initiation of development of the organ systems. One of the most common problems in commercial incubators is the lack of uniformity in providing heat to all the eggs in the incubator cabinet. Low temperatures during the first days of incubation can cause reduced hatch, late hatches and poorer quality hatchlings.
Toward the middle and latter stages of incubation, when there is an increase in metabolic heat produced by the embryo, it becomes important to remove excess heat from the egg. Recent research suggests that eggshell temperature for broilers should be maintained at 37.5-38C. (99.5-100.5F) for best performance in the field.
During the latter stages of development, the yolk is the primary source of energy for embryo development and the embryo’s yolk utilization can be influenced by oxygen partial pressure, temperature, and humidity. Work in our laboratory at North Carolina State University has demonstrated the effects of elevated incubator temperature during the plateau stage of oxygen consumption during incubation.
The utilization of energy from yolk lipids and its nutrients requires oxygen. Embryos also store energy in their liver and muscles as glycogen, a carbohydrate form that does not require oxygen.
When there are elevated temperatures, embryo development accelerates at a rate faster than normal oxygen levels can sustain, and this insufficiency of oxygen causes the yolk to not be utilized to the extent that it ordinarily would.
When this energy is limited from the yolk lipids, then glycogen must become a more important source of energy as oxygen is not required for its metabolism. However, glycogen is not stored in great quantities, and if abnormal incubation conditions exist for extended periods it can result in the developing embryos quickly using up their glycogen reserves. If the chicks do hatch they are generally of poorer quality, appearing lethargic, slow to go to feed and can starve out at the farm increasing the first week mortality.
Our research indicates that elevated temperatures during the last four days of incubation have an adverse effect on embryo development and maturation of organ systems, such as the digestive system. Frequently, the average weight of chicks is reduced by 5% because of elevated hatcher temperatures. This indicates 2-3 g lighter chicks, but the relative weight of gizzard and intestines are reduced by 13% and 16%, respectively. Elevated temperatures reduce both tissue mass of the hatchling and decrease the maltase enzyme in the intestine that is an indicator of intestinal maturation.
Incubation temperature can have an effect upon early muscle development. The specific effects on post-hatch muscle development vary according to when in embryo development the temperature changes or stress occurred.
Our lab has demonstrated in both the broiler and turkey that elevated temperatures during the last four days of incubation have a detrimental effect upon the pipping, thigh, and breast muscles. The pipping, which is a transitory muscle, and the thigh muscle are both very active during the hatching process. The breast muscle is not used for the hatching process, but can be a source of energy substrate if the yolk and other muscle glycogen sources are limiting. The breast muscle is generally richer in glycogen than the other two muscles and also can act as a reservoir for gluconeogenic amino acids, if glucose needs to be made available. If breast muscle is utilized for its gluconeogenic amino acids, however, the number of muscle fibers available for meat production will be reduced.
Additionally, we have demonstrated effects upon the thyroid status of the embryo. Elevated incubational temperatures during the plateau stage of oxygen consumption can produce hypothyroid hatchlings which could impact maturation of other physiological systems, such as the immunological system, thermoregulation, and bone development. There is evidence, that maintaining a cooler eggshell temperature than typically is seen during the latter stages of multistage incubation may lead to lowering the thermoregulatory set point with an ability to compensate with increased heat production, if chicks are exposed to slightly cooler brooding temperatures.
Temperature of the embryo may be the most important parameter for the developing embryo, but ventilation, turning and moisture control are also important in producing high quality chicks. These factors play an important role and can also influence how nutrients are utilized impacting chick quality.