Creating the most realistic nesting conditions is essential to ensure a successful hatchability rate. Temperature can have one of the largest impacts on the incubation period. If the temperature deviates from its optimum level of 37°C through 38°C, then post-hatch growth and organ function of the chickens can be impaired [1]. Heat stress can occur to the chick embryos when facing temperatures above 39°C, resulting in high mortality rates and decreased embryonic development due to limited metabolic process by insufficient exchange of oxygen [2,3]. However, research has shown that a temporary drop in temperature from the optimum level can be seen as beneficial, while a permanent change in temperature decreases the hatchability rate immensely [4]. There is limited to no data around the effects of daily cooling periods where temperatures are dropped to room temperature (21.1°C) for a limited time. This experiment sheds light on the effect of a limited cooling period throughout incubation for 60 minutes daily.
The purpose of this study is to optimize the hatchability of SPF chickens in this vaccine testing facility, in order to create an affordable and effective as pergillosis vaccine. This research will also investigate if cooling periods increase hatchability, as they mimic more natural nesting conditions. This study will examine if heart rate or egg weight loss contributes to hatchability. By emplacing cooling periods, it will be determined if there are any negative side effects, such as dysfunctions or disorders. It is hypothesized that the trials with a cooling period will have higher hatchability rates, due to a more accurate simulation of natural nesting.
The incubation protocol consisted of the 159 SPF chicken eggs being incubated at approximately 37.5°C in an environment with 50-60% humidity, from day 1 to 17. At day 18, the temperature remained the same but the humidity was increased to 65-75% until they hatched on day 21. The increased humidity aids in the chickens’ ability to pip. Throughout the incubation process, the eggs remained in the Brinsea OVA-Easy Advance Series II Incubator. The incubator was set to tilt every 180 minutes up until day 18. The eggs were rotated by hand once a day 90 degrees until day 18 as well. The eggs were rotated to promote embryo growth and to prevent premature adhesion of embryo membranes to the shell. Eggs were candled and weighed after the 1st week and before the 3rd week. Heart rate was also taken on day 18, using the Avitronics Egg Buddy Digital Egg Heart Monitor. Observing heart rate helped with the candling process because eggs in later development stages are difficult to observe movement or indication of growth. Re- candling took place after each candling session if there was any uncertainty with an egg. Culling is an important step in the incubation process. If eggs containing dead embryos are left in the incubator, bacteria may develop and ferment, which could cause an explosion and contamination of the entire clutch of eggs. Culling took place after the two rounds of candling (day 7 and 18) as well as for the eggs that did not hatch (day 23). Euthanasia was used for chicks displaying signs of suffering. Three chicks were euthanized in the first treatment group with a cooling period. One chick exhibited curled toes and could not mobilize normally. This was diagnosed as curled toe paralysis, caused by a B2 deficiency in laying hen. The second chick was resting on its hocks exhibiting, swollen feet and bleeding and bruising at joint. This was diagnosed as slipped tendons, caused by a manganese deficiency in laying hen. The third chick never gained motor skills. This was diagnosed as a neurological issue, due to a vitamin E deficiency in laying hen. None of these signs were present in cooling period treatment group 2, so it is believed deficiencies in the nutrition of the laying hen caused these issues.
Both cooling period treatment groups exhibited the largest amount of egg weight loss towards the end of the incubation period, compared to the other treatment groups (Table 1 & Figure 1).
Figure 1: Average egg weight loss vs. presence of a cooling period.
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Cooling Period Group 1
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Cooling Period Group 2
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No Cooling Period Group 1
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No Cooling Period Group 2
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Average Heart Rate
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245.50 BPM
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235.65 BPM
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230.80 BPM
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249.93 BPM
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Hatchability
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94.90%
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100%
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82.50%
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90%
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Weight Loss
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4.766g
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4.475g
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3.868g
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4.305g
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Table 1: Cooling Period Group and non Cooling Periods.
There is a statistically significant increase in weight loss in groups with a cooling period compared with those without (p < 0.001). The heart rates of all four groups are shown in Table 1 & Figure 2. There is not a statistically significant difference between the presence of a cooling period and heart rate (p = 0.139). Both groups that received the cooling period had a higher hatchability rate compared to the two groups without (Table 1).
Figure 2: Average heart rate vs. presence of a cooling period.