| | Why did we do this experiment?
Management decisions made by primary breeder companies, broiler hatching egg producers, and hatcheries all have an effect on the hatchability and quality of broiler chicks. One of these factors is the length of time that hatching eggs are stored prior to setting in the incubator.
The goals of this project were to
- Determine how egg storage affects hatchability and chick quality.
- Identify possible causes of poor hatchability and chick quality when eggs are stored long term.
- Identify recommendations for the handling of hatching eggs prior to incubation.
Why are hatching eggs stored?
Hatching eggs are stored at the broiler breeder farm and at the hatchery. Storage on-farm reduces transportation costs by eliminating the need for daily egg pick-up. Eggs are stored at the hatchery for one of the following reasons: a) in the case of undersupply, that enough eggs are available to completely fill an incubator; or, in the case of oversupply, eggs are stored until incubator space is available. The eggs are stored in rooms set at about 18oC and 75% relative humidity to prevent development of the embryo and to inhibit bacterial growth. It is common for hatching eggs to be stored for a few days and most hatchery managers try not to store eggs for more than one week.
How was the experiment conducted?
Four separate experiments were conducted. In the first study, embryo development was staged from eggs stored for 4 or 14 days to determine why eggs that are stored for long periods require more incubation time. Embryonic development was staged every 3 hours during the first 24 hours of incubation, every 12 hours from 1½ to 7 days of incubation, and every 24 hours from 7½ to 13½ days of incubation. At 18 days of incubation, 30 eggs per storage treatment group were monitored to establish the amount of incubation time required for hatching. Embryos were weighed every 24 hours beginning at 8½ days of incubation until hatching.
In the second study eggs were stored for 4 or 15 days. Oxygen consumption was measured to establish the metabolic rates of the embryos (how fast they were growing) by placing each egg into a separate metabolic chamber inside the incubator.
The third and fourth studies were conducted at the same time. Hatching eggs were acquired from the same broiler breeder flock at two times - at 33 and 58 weeks of age. Eggs in the third study were stored for 4 or 14 days. Sugar (glycogen) metabolism of in the heart and liver of the newly hatched chicks was measured. Glycogen is the main source of energy available to the embryo during the incubation and hatching process. Heart glycogen was measured as the heart is considered a demand organ (needs glycogen) and liver glycogen was measured as the liver is a supply organ (stores glycogen).
In the fourth study eggs were collected at the same time as study three, but were stored for 16, 14, 12, 10, 8, 6, 4, and 2 days prior to incubation. Hatchability, chick quality and broiler growth was measured. Chicks from the 33-week-old flock were grown out to establish the effects of the storage lengths on mortality and growth. Due to an outbreak of myeloid leukosis in the breeder flock, the chicks from the 58-week-old flock were not grown out for biosecurity reasons.
Embryo development results - Study 1
The cause of delayed hatching in eggs stored for long periods is not clear. Some researchers believe that the initiation of embryo development in long-term stored eggs is delayed after proper incubation temperatures were provided. Other investigators thought that development starts once incubation temperatures were provided, but proceeds at a slower rate (compared to eggs stored for a short period). This study showed that both theories are correct. Some embryos of eggs stored for 14 days did not begin development after the eggs were placed in the incubator, while other embryos began to develop, but grew at slower rates than embryos from eggs stored for only 4 days. Overall, embryos from eggs that were stored for 14 days were significantly less developed and weighed less than embryos of eggs stored for 4 days. On average it took 10 hours longer for chicks from 14 day stored eggs to hatch than chicks from 4 day stored eggs. Chick weight did not vary between eggs stored for 4 or 14 days.
Embryo and chick organ metabolism - Studies 2 & 3
Study 2 showed that starting as early as 4 days of incubation, embryos of eggs stored for 15 days consumed less oxygen than embryos from eggs stored for 4 days. This provides more evidence that embryos from eggs stored long-term have a slower metabolic rate than embryos of eggs stored for short periods. Future research examining methods to increase the metabolism of embryos from long-term stored eggs (i.e. slightly warmer incubation temperatures) may help decrease the incubation time required to hatch long-term stored eggs. In Study 3 the heart and liver metabolism of glycogen (sugar) was indirectly measured in chicks hatching from eggs stored for 4 or 14 days from a 33 and 58 week old breeder flock. Chicks hatching from eggs produced by a 58-week-old flock had higher heart and liver glycogen concentrations than chicks hatching from the 33-week-old flock. As glycogen is the main source of energy used during the hatching process, the fact that glycogen reserves in the older flock were not depleted as much as the young flock is an indication that the chicks are less stressed. This may partially explain the poultry industry's general observations that chicks from older breeder flocks have a greater livability. Reduced stores of glycogen were found in chicks hatching from eggs stored for 14 versus 4 days. Again, these differences in sugar metabolism may pose a survival threat to chicks hatching from long-term stored eggs.
Hatchability, chick quality, and broiler growth in a 33 week old flock - Study 4
The significant results from the fourth study are summarized in Table 1. Weight gain and feed conversion throughout the six week grow out period was not influenced by egg storage length. Breast muscle weight did not vary between the birds hatching from the eggs stored for various lengths of time. As expected the hatchability of fertile eggs suffered when eggs were stored longer than six days (Table 1). Chick weight at placement was also negatively affected; chicks from eggs stored for 12 days or longer weighed significantly less than chicks from eggs stored for 4 days. There was a general decreasing trend in eviscerated body weights at processing as storage length increased; birds hatching from eggs stored for 14 days had lower eviscerated weights than birds from eggs stored for 4 days.
Summary
Embryos and chicks from long term stored eggs have metabolically different than embryos and chicks from short term stored eggs. When eggs are stored for 14 days very early embryo development does not progress normally. The investigators of these studies believe that the embryos are shocked when they are exposed to long term storage. Basic research is currently underway to determine if embryos from long-term stored eggs have more cells dying during storage compared to embryos from short term stored eggs. Even though broiler weight gains were not affected by the various egg storage lengths throughout the grow-out period, final eviscerated body weights did not seem to recover when chick weights were low at the time of placement. The higher reliance of chicks from 14 day stored eggs on sugar reserves may place them in a vulnerable position at the start of the grow out period.
Table 1. The effects of egg storage length on hatchability, chick weight, and eviscerated carcass weight.
| Egg Storage Length (days) | | | | | | | | |
| | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 |
| Hatchability of Fertile Eggs (%) | 83.4a | 81.3a | 79.7a | 73.3b | 68.9c | 68.2c | 66.9c | 61.1d |
| Chick weight (g) | 42.9ab | 43.3a | 42.9ab | 42.8abc | 42.9abc | 42.1cd | 41.7de | 42.2bce |
| Eviscerated weight (g) | 1517a | 1509ab | 1517a | 1470bc | 1501ac | 1513a | 1464c | 1502ac |
a-eValues within a row with different superscripts are significantly different from one another.
Gaylene Fasenko and Frank Robinson
Poultry Research Centre News Vol 10 No 2, October 2001
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