Hatchery Management
By James S. Stewart, DVM

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Egg Handling Before Incubation

Collection and Transportation

Ostriches generally lay eggs in the late afternoon and evening, and the eggs should be collected as soon as possible afterward. Ideally, egg collections are made several times per day with the last collection at sundown. Eggs left in the nest are frequently rolled about and occasionally consumed by curious adult ostriches and are also subject to shell damage. Eggs left overnight in the nest may cool, drawing bacteria into the egg through the pores. Shell sanitation of internally contaminated eggs is of little value and hatchability is reduced. Eggs left in the nest for several days are subject to extremes of environmental temperature, particularly when exposed to direct sunlight; the result is high incidence of early embryonic mortality.

Ostriches, unlike poultry, are bred in outdoor paddocks, and egg collection must necessarily be done by hand. Large numbers of eggs are usually accumulated in padded crates to minimize shaking and promptly transported by vehicle to the hatchery. Eggs collected from the wild or from extensive management systems, such as game parks, are usually already partially incubated, and particular care must be taken to prevent shaking and cooling of the developing embryo or the decreasing hatchability will be substantial.

Eggs should be identified at the time of collection. The pen number, hen number, or other means of identifying parentage is necessary to evaluate productivity and may safely be written on the eggshell with a pencil. All desired data should be quickly collected and logged in incubation records before the eggs are sanitized and stored.

Sanitation

An egg possesses several natural defenses against penetration and growth of infectious agents. First, the cuticle is a layer of mucus that dries onto the shell surface shortly after the egg is laid, and initially plugs the pores of the shell to act as the principal physical barrier to infectious agents. Second, most of the pores of the shell are small enough to prevent bacterial passage, but a certain percentage are large enough to allow infection. Shell membranes serve as a third but minor physical barrier to infection. Within the albumen, several vitamins and minerals are bound to proteins that make them unavailable to bacteria, thus inhibiting bacterial growth. Lastly, the developing embryo acquires a certain amount of passive immunity from immunoglobulins present within the yolk that allow it to fend off infections to a limited extent.

The most important aspect in the reduction of egg contamination is the production of a clean egg. Ostrich management practices require that eggs be laid in nests formed as shallow depressions in the ground. This is a significant sanitation compromise compared with indoor commercial poultry practices. It is imperative that the nests be as clean and dry as possible and that the eggs be collected promptly. Sand placed in the selected nest site provides a reasonably clean substrate and good drainage and is usually acceptable to adult birds. Disinfection of the nest site is advocated by some breeders, but its efficacy remains to be proven. However, because ostrich eggs are laid on the ground, virtually all have some dust and dirt on the shell surface and in the pore openings.

Egg sanitation methods remain controversial even within the commercial poultry industry. Modern mechanical egg washers are not currently used in ostrich hatcheries because of the limited scale of production. Consequently, egg sanitation procedures, if any, are performed by hand. Common practices have been to remove dirt with sandpaper, or to wash eggs in warm solutions of dilute sodium hypochorite, chlorhexidine, quaternary ammonia, or phenolic or disinfectant compounds. These methods destroy the cuticle and reduce the resistance to subsequent bacterial penetration, and practical experience has demonstrated that these methods generally increase the incidence of infection in clean eggs compared with that obtained with no treatment.

Current practice of the hand cleaning of ostrich eggs advocates a dry removal of dust and dirt followed by the application of disinfectant mists. A dry egg is lightly buffed with a soft-bristle shoe brush as a simple means of removing the bulk of the dirt, especially from pore openings, without destroying the cuticle. If the egg is wet or contaminated with moist dirt, the surface is dried with a hot air blow drier and then buffed. The egg surface is coated with a fine layer of commercial poultry egg disinfectant solution containing either quaternary ammonia or phenolic compound. This is applied either by hand spraying, aerosol, or fogging system and allowed to dry. The egg is then placed in storage. Formaldehyde gas, although effective as a fumigant, is extremely irritating to both human and avian mucous membranes, carcinogenic, and environmentally hazardous. Because safe and effective alternatives are readily available, the use of formaldehyde gas fumigation is contraindicated.

Storage

Egg storage before incubation significantly increases hatchery management efficiency by allowing the batch processing of eggs. When performed properly, cold storage is of no detriment to hatchability. The threshold temperature for avian embryonic growth is 20°C (75°F). Ostrich eggs held at or above this temperature show a marked increase in early embryonic mortality after the second day. Eggs maintained between 12.8 to 18.3°C (55 to 65°F) may be safely stored for one week, but hatchability will be significantly reduced at two weeks. Relative humidity near 75% is recommended to prevent excess evaporative water loss from the eggs during storage.

Eggs should be placed on clean wire racks within the storage cabinet or room. If eggs are positioned air cell upward in the incubator tray, the entire tray can be transferred without handling and contaminating the individual eggs. The air cell can be identified shortly after the egg is laid by illuminating the end of the egg in a completely darkened room with a small flashlight that makes a light-tight seal with the egg surface. Alternatively, eggs may be stored horizontally. There is evidence in poultry that eggs stored air cell upward have a slightly lower hatchability, but the repositioning of eggs at the end of storage is an extra management step that also increases exposure to bacterial contamination. Eggs do not need to be turned if stored for one week or less. If stored for longer periods, eggs should be turned once daily, but prolonged storage is not recommended because of the associated reduced hatchability.

Incubation

Temperature

Ostrich eggs can be successfully hatched at temperatures from 35° to 36.9°C (95 to 98.5°F), but most producers operate incubators at a setting between 36 and 36.4°C (96.8 to 97.5°F). Constancy of temperature is critical because fluctuating temperatures result in poor hatchability and unthrifty chicks. The optimum incubation temperature for ostriches has not as yet been experimentally determined, but should be expected to vary slightly with egg quality, humidity, and incubator design.

Increased temperature shortens the incubation period for the ostrich by approximately one day for each 0.6°C (1.0°F) temperature rise, so that incubation time is an average of 45 days at 35.6°C (95.0°F) and 42 days at 36.7°C (98.0°F). However, excessively high temperatures may increase the rate of embryonic mortality at any stage of development, augment the incidence of malformed chicks, and induce the chicks to pip and hatch too early. High incubation temperatures have been implicated in malformations of the eyes and limbs of the ostrich in particular.

Low incubation temperatures also increase the incidence of embryonic mortality and result in soft, weak chicks that hatch late. Embryos possess a limited resistance to cool temperatures that may result from electrical failures at the incubation facility. Chicken embryos can tolerate a decrease in temperature to 18.3°C (65°F) for a few hours during early and midembryonic development with little effect on hatchability, but such cooling is disastrous during the last few days of incubation. This is also consistent with clinical observations of the ostrich. Power failures lasting several hours at ostrich facilities have been noted to induce mortality in embryos at 35 or more days of incubation but to have little effect on younger embryos; it is consequently recommended that a standby electric generator be installed as standard equipment in all ostrich incubation facilities.

Humidity

The level of humidity in the incubator regulates water evaporation from an egg during incubation. The amount of evaporative water loss determines the size of both chick and air cell. Low water loss results in a weak, edematous chick and a small air cell; high water loss results in a weak, dehydrated chick and a large air cell. Water loss is monitored by measuring the decrease in egg weight through the course of incubation. The desirable weight loss for ostrich eggs from set to internal pipping is 12 to 15% of initial weight. Ostrich eggs with a weight loss below 12% show poor hatchability, and below 10% hatch only rarely without assistance. Ostrich chicks from eggs with excessive weight loss have good hatchability, but hatch early, with reduced survival.

Humidity settings for the incubation of ostrich eggs currently range between 25 and 40% relative humidity. The particular selection depends on the temperature, egg quality, and air circulation. Higher incubation temperatures require lower humidity to maintain hatchability. Higher temperatures increase the metabolic rate of the embryo and the amount of metabolic water produced, and shorten the incubation period during which evaporation occurs. The reverse holds true for lower temperatures. On the average, large eggs and those with thick shells lose less weight than do small or thin-shelled eggs. As indicated previously, the wide variation in these qualities among ostrich eggs results in a wide variation in measured parameters. In a group of 179 ostrich eggs (1319 to 1925 g; mean, 1663) incubated at 35.8°C (96.5°F) and 33% relative humidity in a single incubator, weight loss varied from 8.5 to 23.6% with a mean of 13.2%. Ideally, eggs would be sorted by size and shell quality and incubated under different conditions to compensate for the variability. Most commonly, however, appropriate incubation humidity for the ostrich is determined as the setting that produces an acceptable average weight loss from all eggs.

Air Circulation and Ventilation

Circulation refers to the movement of air within the incubator, whereas ventilation refers to the exchange of air between the incubator and the surrounding environment. Air circulation is critical to uniformity of temperature, humidity, oxygen, and carbon dioxide throughout the incubator. Circulation is provided by various types of paddles or fans that move air in a specific pattern for each type of incubator and should be tested and proved by the manufacturer. In general, the greater the airflow created, the more uniform the air mixture.

The velocity of airflow has little apparent effect on hatchability in poultry, but ostrich eggs incubated in cabinets with low internal air velocity routinely have low total water loss, even at very low humidity settings. This may be explained by the boundary layer effect of a very large egg that results in a zone of still air near the surface. Because the dissipation of both water and heat generated by the embryo is reduced, the egg is housed in a microenvironment characterized by higher humidity and temperature than that indicated by the machine settings. Consequently, evaporative water loss is reduced and metabolic water production is increased and the cumulative effects result in weak, edematous chicks.

Ventilation is required to supply an adequate level of oxygen to the incubation environment and to exhaust excess carbon dioxide from it. Atmospheric air includes 20.95% oxygen and 0.03% carbon dioxide at sea level. Commercial poultry recommendations are that oxygen concentrations not fall below 20.5% and carbon dioxide not exceed 0.5%. Hatchability drops about 5% for each 1% decrease in oxygen, and carbon dioxide concentrations above 1.5% yield disastrous results. Oxygen consumption of ostrich eggs has been measured and it can be extrapolated that, at peak metabolism, 200 ostrich eggs are the approximate metabolic equivalent of 1000 chicken eggs. Ventilation recommendations for poultry are generally 2.5 to 3.4 m (90 to 120 ft.) of fresh air per hour per 1000 eggs, and the equivalent ventilation for 200 ostrich eggs should be adequate.

Ventilation also serves to control humidity for most incubators. Cool room air brought to incubation temperature has the potential to hold more moisture, and relative humidity is consequently lowered. Increased ventilation draws more cool air into the incubator to lower the humidity level. Conversely, closure of the ventilation ports increases humidity. To attain the low humidity settings required for the incubation of ostrich eggs, it is imperative that the incubator room air be cooled. Air temperatures in the range of 22.0 to 24°C (71.6 to 75.2°F) are recommended. The ventilation of cool air directly into the incubator can create low temperature pockets near the inlet ports; therefore, ostrich incubators should be constructed with premixing chambers in which fresh air may be warmed by recirculated air before it enters the incubation compartment.

Position

Ostrich eggs should be set in the incubator trays in a vertical position with the air cell upward to prevent embryonic malpositions. The normal position of the chick within the egg is with the legs bent on either side of the abdomen so that the feet are ventral to the shoulders (as in a crouching position). The neck is bent ventrally, and the head rotated to the right, with the beak situated near the right foot and shoulder. The spine is along the long axis of the egg, and the head is at the air cell pole so the chick can penetrate the inner shell membrane at pipping, and commence pulmonary respiration within the air cell space.

The embryonic malposition commonly referred to as the backward chick is of particular significance in ostrich incubation. The chick is reversed in the egg with the head located at the opposite end from the air cell. Such chicks are unable to pip into the air cell before hatching and their mortality rate is severe. In poultry, the incidence of this malposition is approximately 2% from eggs incubated air cell upward and 4% from eggs incubated horizontally. In the ostrich, however, the incidence of 3% from eggs incubated air cell upward increases to 16 to 20% when egg are incubated in a horizontal position.

The orientation of the ostrich chick is determined between the 7th and 10th day of incubation when the yolk and embryo fix rather than float freely within the albumen. A common protocol for ostrich eggs has been to incubate horizontally for 10 days, when the eggs are candled for fertility and repositioned air cell upward. However, with this protocol the incidence of malpositions is the same as occurs with continued horizontal incubation. It is imperative the eggs be positioned air cell upward within the first week, and preferably at set. As indicated above, the air cell may be readily identified with the use of a small flashlight.

Turning

Avian eggs should be rotated periodically during incubation to stir the layers of nutrients and waste products around the developing early embryo. Eggs turned too infrequently show a low hatchability and a high incidence of embryonic malpositions. It has been demonstrated in poultry that rotating eggs to a position 45° from vertical at least six times per day results in optimal hatchability. Until research has demonstrated otherwise, it should be assumed that the same applies to the ostrich. Most modern ostrich incubators automatically turn eggs hourly. The traditional practice of hand turning eggs three times per day is probably inadequate, greatly increases bacterial contamination, and should be abandoned.

Candling

Candling is a means to identify nonviable eggs. Nonviable eggs should be removed from the incubator because they waste space, are a source of excess evaporative water vapor, and pose a potential threat for incubator contamination. A common egg candling device consists of a bright light encased in a box or tube with an opening in the top. The eggs are individually placed over the opening in a dark room and the contents are illuminated from below. A preferred alternative is to illuminate eggs from below with a small, bright flashlight while they are still in the incubator trays. This procedure is more efficient and eliminates unnecessary handling and contamination of viable eggs.

The shadow created by the yolk, embryo, and extraembryonic membranes changes during the course of incubation and is indicative of embryo viability. The common practice of candling weekly is interesting and educational to the novice but is of no practical value in commercial ostrich production. Candling need be performed only once during incubation and again at transfer to the hatcher. If eggs are processed in weekly batches, the recommended time for candling is at 14 days of incubation. Egg viability is readily determined at this state of development, and with this schedule, egg loading and candling are performed on the same day of the week to reduce contamination of the incubator.

Next page: Hatching

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