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Anatomy
All female ratites have a single left ovary and oviduct. The oviduct consists of 1) the infundibulum where fertilization occurs, 2) the magnum where the thick albumin is put on, 3) the isthmus where the inner and outer shell membranes are added, 4) the uterus where the shell is added, and 5) the vagina. The opening of the vagina into the cloaca is on the left side of the cloaca at the ten o'clock position.
The male ratite has 2 intra-abdominal testicles that are located near the kidneys. During the breeding season, the testicles increase 200–300% in size. The rooster does not produce sperm when he is not in season. Roosters in the ratite family all have a phallus that serves to transport semen from the ejaculatory ducts in the cloaca of the male to the cloaca of the female. The phallus is shaped differently in the ostrich, emu, and rhea; however, the function is the same. All have a dorsal groove through which the semen travels.
Breeding
The ostrich and rhea are long day breeders. The season is controlled by the photoperiod (length of daylight) as well as the ambient temperature. In North America, the breeding season is spring and summer for these birds. The emu is a short day breeder and lays in the late fall and winter. Once the breeding season has started, the cock and hen become behaviorally active. The ostrich cock develops his colors and begins to display and the hen begins to flutter. This behavior continues for days to weeks before egg laying begins. In general, the female comes into season before the male. Therefore, early eggs are often infertile. This is also true for the emu and rhea. The ostrich hen lays every other day during the proper season if the eggs are collected daily. In the wild, normal clutch sizes for ratites are 15–25 eggs; 30 is the average for these birds in captive rearing. The range is from 0 to 167 consecutive eggs.
Hatching
If eggs are gathered and stored for “batch setting,” they should be cooled, if possible, to 60°F. Physiologic zero—or the point at which the embryo stops developing—is 72°F. The egg is laid with the embryo in the 60,000 cell stage, and cooling the egg before incubation ensures that all cells develop in synchrony. In general, hatching eggs should not be washed if they are clean. If eggs are wet or dirty, they should be washed in a warm 110°F disinfectant solution (eg, chlorhexidine, sodium hypochlorite, quaternary ammonia) before cooling.
Incubation of eggs is commercially done in forced air incubators. Ostrich eggs generally are incubated at 97°F (36.1°C) for 40–42 days and moved to the hatcher at 40 days or when the chick “pips” (breaks the egg). Emu eggs are incubated at 97–98°F for 54–58 days and moved to the hatcher at 50–52 days or at “pipping.” Rhea eggs are incubated at 98°F for 40 days and moved to the hatcher at 38 days or at “pipping.” While temperature in the hatcher is the same as incubation, the humidity should be higher.
Hatchery operations should observe good basic management and biosecurity practices, including “all-in /all-out” management. Groups should be placed in an area of adequate space, heat, and ventilation, with fresh water and feed. Mixing of groups should be avoided (to reduce stress) until chicks are at least 3 mo old.
Reproductive Diseases
Many diseases can result in reproductive failure, either through failure to produce eggs or through production of abnormal or contaminated eggs. Bacterial salpingitis or metritis is common. The etiologic agents vary, as does the severity of the infection. In mild cases, only the uterus or shell gland is affected (metritis), and clinical signs range from abnormal shells to no egg production at all. Infection may result from retrograde bacterial invasion (from breeding or uterine fatigue), extension of an airsacculitis, or a perforation of the abdominal cavity by a foreign body. Affected hens generally have a history of erratic egg production, malformed or odoriferous eggs, or a sudden stop in production. On physical examination, temperature and respiration are variable, there may be a discharge below the cloaca, and hens may have a fetid odor. Affected hens have WBC counts ranging from 8,000 to >100,000. Ultrasonography and radiology are useful in assessing the amount and consistency of exudates in the oviduct. Treatment is based on culture and sensitivity.
Last full review/revision July 2011 by Karen Hicks-Alldredge, DVM
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