Age Changes in Digestibility of Nutrients in Ostriches and Nutrient Profiles of Ostrich and Emu Eggs as Indicators of Nutritional Status of the Hen and Chick


C. Roselina Angel, Ph.D. Purina Mills, Inc.
P.O. Box 66812 St. Louis, MO 63166
(Note: This article first appeared in the 1993 Proceedings of the Association of Avian Veterinarians. It is reprinted with permission.)


A digestibility study was conducted with 3, 6, 10, 17 week old and 30 month old ostriches. Metabolizable energy (ME) values and fat and neutral detergent fiber (NDF) digestibilities were determined. The formulated ME of the diet (chicken ME basis) was 1983 kcal/kg. The determined values with ostriches were: 3 weeks, 1731; 6 weeks,
2337; 10 weeks,2684; 17 weeks, 2739; and 30 months, 2801 kcal/kg. Fat digestibility was 44.1 percent at 3 weeks and 91.1 percent by 17 weeks of age. NDF digestibility was 6.5 percent at 3 weeks, 51 percent at 10 weeks and 61.6 percent at 30 months. Also, vitamin and mineral levels were determined in the eggs of ostriches and emus and compared with poultry values. Deficiencies or excesses of vitamins and/or minerals in the laying hen, and thus in the egg, can lead to infertility, poor hatchability and early chick health problems. Specifics are described.


The digestibility of different nutrients by an animal is a good indicator of how well the animal can process the derive nutrients from a given diet. Digestibility of nutrients changes with age and tends to be low at young ages1. Extensive work done with chickens2 and turkeys1 has shown that dry matter, protein and fat digestion are low at early ages. This low digestive capability early in the life of these precocial birds is due mainly to the low levels of digestive enzymes found in the intestinal tract at hatch and for a few weeks after hatch1.
In ratites, there is a limited amount of information available in the literature relating to digestibility of nutrients and digestive enzyme levels. Extensive research has been done on characterization of pancreatic enzymes but there are no reports of actual enzyme levels. Researchers have studied fiber digestion in emus3 and ostriches4. Research has also been done with emus, in which metabolizable energy values and dry matter and nitrogen digestibility were determined5. In each of these studies, the researchers used adult birds, and digestibility values were obtained at only one age. Swart et al.4 found that adult ostriches digested 63 percent of the cell wall constituents or neutral detergent fiber (NDF) in a high fiber diet. Herd and Dawson4 found an NDF digestibility of 45 percent in emus fed a high fiber diet (36 percent NDF).

Materials and Methods

The objective of the research presented here was to determine metabolizable energy values and fiber and fat digestibility at different ages in the ostrich. Two replicates were used per age group. The ages studied were: 3 weeks (three birds per replicate), 6 weeks (three birds per replicate), 10 weeks (three birds per replicate), 17 weeks (two
birds per replicate), 30 months (two birds per replicate). The birds were fed the same diet at all ages. The diet was formulated to contain 24 percent protein, 7 percent fat,
16.6 percent crude fiber, 33.3 percent NDF, and an ME (metabolizable energy) value of 1983 kcal/kg (based on chicken ME values). The analyzed values for the diet fed were similar to those formulated (24.1 percent protein, 7.3 percent fat, 16.7 percent crude fiber and 33.9 percent NDF). Chromic oxide was used as an indigestible marker at .3 percent of the diet. The fat added in this diet was crude soybean oil.
The birds were adjusted to the new diet for 7 days. After the 7 day adjustment period, excreta (feces and urine) were collected for 24 hours. The excreta samples were frozen immediately and stored at -10 degrees Fahrenheit until analyzed. Feed and excreta samples were analyzed for dry matter by drying for 48 hours at 70 degrees Celsius in a force draft oven; gross energy (GE) by using an adiabatic bomb calorimeter; fat by petroleum ether extraction after acid hydrolysis (AOAC6); chromic oxide by the procedure described by Fenton and Fenton7; crude fiber and NDF as described by Van Soest8. The nitrogen corrected ME of the diet was calculated on the basis of diet and excreta GE and chromic oxide levels using the methods described by Hill and Anderson9. The data obtained were analyzed statistically by analysis of variance to determine age differences, in accordance with the procedures outlined by Snedecor and Cochram10.

Results and Discussion

The formulated ME was derived using book energy values (NRC, 198411) for poultry (chickens). When using poultry values, it is important to keep in mind that poultry do not digest fiber well (5 to 6 percent of NDF12). It is also important to note that fat retention of an animal-vegetable fat source in poultry has been shown to be 80 percent at 2 weeks of age and 93 percent by 8 weeks of age13.
In ostriches, at 3 weeks of age the determined ME was lower than the formulated value (1731 versus 1983 kcal/kg, respectively) (Table 1). This was probably due to the relatively low fat digestibility value obtained with 3 week old ostriches (44.1 percent) versus that expected in chickens. By 6 weeks of age, the determined ME was 606 kcal/kg higher than formulated and higher (P<.05) than at 3 weeks of age. By this time (6 weeks), the ostrich chicks were digesting fat to a greater degree (P<.05) than at 3 weeks and fiber digestibility was higher than would be expected for turkeys. Average fiber digestibility in adult chickens is less than 6 percent12. At 10 weeks of age, ostriches had a higher (P<.05) ME than at 6 weeks of age. The ME was similar at 10 and 17 weeks at age. In the adult bird (30 months), the ME was 818 kcal/kg higher or 41 percent higher than the formulated value, and significantly higher (P<.05) than at 17 weeks of age. The high ME value as compared to formulated was mainly due to the greater NDF digestibility determined in adult ostriches.
Fiber digestibility was low at 3 weeks of age, but increased linearly up to 10 weeks of age, with a significant (P<.05) increase at each age. After 10 weeks of age, the ability of the ostrich to digest fiber continued to increase, but at a slower rate, reaching a plateau at 17 weeks of age. The NDF digestibility obtained in this study with adult birds is similar to that obtained previously by Swart et al.4 (61.6 versus 63, respectively).
Apparent fat digestibility was low (44.1 percent) at 3 weeks of age in ostriches. In 2 week old turkeys, fat retention has been found to be 80 percent13. There was a dramatic
improvement (P<.05) in fat digestibility in ostriches at 6 weeks of age as compared to improve up to 17 weeks of age. No further improvements were observed with adult birds. Fat digestibility in adult ostriches is similar to that seen in adult poultry13.
The information obtained in this digestibility study suggests that when ostrich diets are formulated using chicken ME values the actual energy value for ostriches is being underestimated by 41 percent. This is especially true for adult ostriches. Lower, but significant, underestimations of energy in the diet also occur when the chicken ME system is being used to formulate diets for ostriches 6 weeks or older.
This research does not provide nutrient ME values for ostriches. One of the challenges for the future is to start establishing ingredient ME values for ostriches. It is important that care be taken when evaluating or formulating growing, breeding and maintenance diets for ostriches in terms of actual energy present and the ratio of energy to other nutrients.
Young ostriches cannot digest fat well. Thus starter diets should not contain very high levels of fat. Field observations have shown that diets with 10 percent fat have resulted in diarrhea. Ostriches 6 weeks or older are capable of digesting fat well, and thus of handling diets with higher levels of fat.
The NDF digestibilities determined in this study show that the 3 week old ostrich does not digest fiber well. Given that the development of fiber digestion occurs slowly and requires the presence of fiber, starter diets should have a moderate level of fiber, starter diets should have a moderate level of fiber. Older ostriches are capable of extensive fiber digestion, and thus of utilizing diets with high fiber levels.
Table 1 Apparent Metabolizable Energy Values and Apparent Neutral Detergent Fiber and Fat Digestibility of a Diet as Determined With Ostriches of Different Ages
Metabolizable Energy Kcal/kg
Neutral Detergent Fiber Digestibility %  
Fat Digestibility %
Formulated Diet Values 1983    
3 weeks 1731a 6.5a 44.1a
6 weeks 2337b 27.9b 74.3b
10 weeks 2684c 51.2c 85.7c
17 weeks 2739cd 58.0d 91.1d
30 months 2801d 61.6d 92.9d
Standard Error of the Means  
Means within columns with different superscript differ (P<.05).  


The data presented in this portion of the paper is preliminary and is meant to serve as a starting guideline for mean nutrient values in the eggs of hens fed with feeds available during 1992 and 1993.
Ostrich and emu eggs were obtained from farms in Texas, Arkansas, and Indiana. Eggs were obtained from hens with a known feed history. At least 3 different types of feed from different feed suppliers were fed to the hens sampled. The values presented in Table 2 represent mean values for the number of eggs sampled to date. Sub-sampling has been done for a limited number of eggs from specific hens where the feed was also analyzed. This provides some indication of how well feed nutrients are being incorporated into the egg.
In the review done by Naber16 on the effect of nutrients on egg composition, he states that some nutrients in the egg are not influenced by diet. The following nutrients in the egg content show little to no variation to changes in the diet: water, protein, fat, calcium phosphorus, amino acids, magnesium16 to be very responsive to dietary changes (vitamins A, D, E, K, and B12, thiamin, riboflavin, pantothenic acid, folic acid, biotin, linoleic acid, manganese, iodine).
Moisture, protein and fat content in the ostrich and chicken eggs appear to be very similar (Table 2). Emu eggs tend to be slightly lower in protein and higher in fat, but the values are not significantly different given the high standard deviation seen.
The key areas to emphasize from Table 2 are: vitamins E and A, folic acid, pantothenic acid, manganese, and selenium. Vitamin A and folic acid are relatively low in emu eggs, but not in ostrich eggs as compared with chicken values. This may be caused by the low feed consumption levels of emus during breeding.
Vitamin E is a key vitamin for reproduction. In both ostriches and emus, vitamin E in the egg is very low compared to normal values in chickens. Preliminary results from sub- samples have shown that levels of 100 IU/kg of vitamin E in the diet result in egg levels of .075 IU/g of egg content on a dry matter basis (unpublished data). Further work is needed to determine the levels of vitamin E in the diet necessary to provide higher levels in the egg content. It will also be important to determine whether there are some forms of vitamin E that are better absorbed than others.
While doing the egg sampling work we have observed what appears to be a selenium toxicity problem (values from eggs obtained from hens being supplemented with high levels of selenium were not used to obtain the mean values). Levels as high as 6.7 ppm were found in the egg content (dry matter) of eggs from laying hens consuming diets with high selenium (from selenium supplementation). It is important to note that both ostrich and emu egg levels are higher than poultry levels and that supplementation with selenium is not advised unless specifically indicated.
Manganese appears to be low both in ostrich and emu eggs. In preliminary studies, diet values of 195 ppm resulted in levels of 9.5 ppm in the egg content dry matter. High calcium and phosphorus intakes aggravate the manganese deficiency by impairing
manganese absorption. Thus it is important to look at the whole diet nutrient content (together with any supplements the producer is using) to evaluate deficiencies.
Table 2 Nutrient Content of Ostrich, Emu and Chicken Eggs
(egg content only).
Nutrient Ostrich n=20 Emu n=14 Chicken1
  means (standard deviation)
Moisture, % 75.12 (1.32) 73.92 (1.65) 74.7
(Dry Matter Basis      
Protein, % 47.1 (1.8) 42.9 (2.4) 47.7
Fat, % 43.7 (2.3) 48.1 (2.4) 45.4
Calcium, % .260 (.02) .245 (.024) .233
Phosphorus, % .798 (.1) .817 (.2) .810
Vitamin A, IU/g 19.29 (7.5) 13.1 (6.1) 20.5
Vitamin E, IU/g .062 (.02) .045 (.02) .12
Folic Acid, ppm 1.93 (.6) .511 (.25) 1.18
Pantothenic Acid, ppm 30.1 (9.1) 36.8 (11.2) 55.3
Riboflavin, ppm 9.72 (1.9) 11.87 (2.3) 12.6
Thiamin, ppm 5.85 (1.3) 2.43 (.72) 3.55
Magnesium, ppm 559.0 (51) 510.0 (63) 490.0
Manganese, ppm 6.6 (2.4) 3.4 (1.1) 15.8
Selenium, ppm 1.57 (.6) 1.18 (.42) .60
Zinc, ppm 53.7 (6.1) 38.5 (5.9) 59.2
Iodine, ppm 3.2 (.78) 3.05 (.89) 2.8
Iron, ppm 101.3 (7.1) 98.3 (6.3) 90.9
1 From: Cotterill et al.14, Latshaw and Osman15.
2 Values corrected for moisture loss during incubation (emu
eggs were obtained after 55 days of incubation and ostrich eggs were obtained after 14 days of incubation).
Table 3 summarizes the potential effects of dietary deficiencies on embryos, reproduction and very young chicks as elucidated in poultry. These are guidelines to keep in mind that reproductive, hatching and early chick problems can be related to factors other than nutrition. All factors must be considered when looking for potential causes, factors such as: incubation and hatching (temperature, humidity, weight loss, egg turning, sterility of incubation environment, and air movement in incubator), egg  pick up routine, egg handling and storage before incubation , health of reproductive pair (to prevent vertically transmitted diseases), overall sanitation of eggs and in the incubator and hatcher (and the rooms they are in), and diet.
Table 3 Effects on the Embryo, Egg, Hen and Chick of Deficiencies of Vitamins and Minerals (From Poultry NRC, 198411)
Vitamin A -Early mortality - failure to develop a circulatory system
  -Low egg production
Vitamin D -Stunting
  -Soft bones
  -Late embryonic mortality
  -Shortened upper mandible in embryo
  -Thin shells or shell-less eggs
  -Low egg production
Vitamin E -Early embryonic mortality - circulatory failure
  -Late mortality - hemorrhages and disturbances in circulatory system
  -High mortality of chicks soon after hatch
  -Low hatchability
  -Prolonged deficiency in males causes permanent sterility
Riboflavin -High mortality in middle of incubation period - dwarfing, edema, defect in the down development
Folic Acid -Late embryonic mortality
  -Bending of the tibiotarsus
  -Defects of the mandible
  -Reduced hatchability
  -Twisted hocks
Pantothenic Acid -Very late mortality without characteristic signs
  -Low hatchability
  -Weak chicks
Manganese -Shortened bones
  -Skull deformities, parrot beak
  -Low egg production
Zinc -Skeletal deformities involving the head, limbs and vertebrae - faulty spine and limb development, caudal part of trunk absent, small eyes, limbs missing
Iodine -Enlarged thyroid gland
  -Incomplete closure of navel
  -Prolonged incubation time
  -Decreased hatchability
  -Decrease egg production
Selenium17 Deficiency
  -Low egg production
  -Very low hatchability Excess
  -Reduced egg production
  -Reduced hatchability
  -Embryonic abnormalities


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