An emu’s digestive system comprises an oesophagus, proventriculus, gizzard, a small intestine (duodenum, jejunum and ileum), caeca, rectum and cloaca. In this respect they are similar to poultry with the exception that they have no distinct crop. The proventriculus, however, is quite distensible and possibly could serve as an organ for food storage. Relative to its liveweight, the length of an emu’s digestive tract is approximately 10 times less than that of domestic fowl.
The time taken for food to pass through the digestive tract is variable, depending in part on the item ingested. Plant particulate matter will take an average of five to six hours, intact wheat grains from less than a day up to two days. Glass marbles have been observed to be retained for 100 days. It would be expected that large particles of insoluble grit would be retained for a period in the gizzard and be effective in aiding the physical maceration of food.
Nutritional requirements
In considering nutrition we are primarily concerned with supplying the emu with all the nutrients essential to its maintenance, growth and reproduction. The nutritional requirements of emus are not yet fully understood.
Energy
Ingredients high in carbohydrates and/or fats are energy sources and include the cereal grains and full-fat soyabean meal, for example.
Protein
Feed protein is broken down in the intestines into its constituent amino acids which may then be absorbed into the blood and used for muscle growth. The emu´s requirement for protein is in effect a requirement for amino acids and it is the amino acid composition of the feed that is the crucial factor. There are more than 20 amino acids of which about 11 cannot be manufactured by the emu and so must be present in the feed. Of these methionine, lysine, threonine, isoleucine and tryptophan are likely to be in shortest supply in emu diets.
Vitamins
These are substances distinct from protein, carbohydrate or fat but which are essential in small amounts for normal growth, development and health. They must be present in the diet although some vitamins may be obtained by coprophagy or be synthesised by micro-organisms in the intestinal tract.
Minerals
These are essential for normal growth, development and health. They must be present in the diet either in relatively small amounts, for example calcium, phosphorus, manganese, sodium and chloride or only trace amounts, for example potassium, iron, copper, iodine, zinc, selenium.
Fibre
Emus can digest only about 20% of the cellulose and lignin in their diet. It has been estimated that the energy derived from this can satisfy about 11% of their energy requirement for maintenance. Their limited capacity to digest fibre is consistent with the observation that, in the wild, emus eat large insects, small vertebrates and those parts of plants in which nutrients are concentrated such as growing shoots, flowers, fruits and seeds. It also suggests that immature, rapidly growing emus should be fed diets relatively low in fibre and similar in nature to conventional poultry grower diets. Some fibre is necessary to promote healthy gut function but in nutritional terms its value is low.
Supplying Nutritional Requirements
The ability to supply emus’ nutritional requirements depends on the feed composition, that is, the concentrations of essential nutrients in the feed and the amount of feed consumed by the birds. When all of the emus’ diet comprises a compounded feed, quite precise control can be had over their intake of nutrients. When a proportion of their diet is derived from the paddock then their quantitative intake of available nutrients is less predictable.
For rapidly growing emus destined for slaughter it seems logical to reduce the dependence on paddock and instead supply compounded diets formulated to least-cost specifications.
The growth curve of emus suggests that a three-phase system of feeding may be appropriate. Phase one could be known as a starter phase and would cover the period from hatching to when the emus attained an average liveweight of approximately 10 kg (14 weeks of age). Phase two, a grower phase, would cover the period from 10 kg liveweight to 25 kg liveweight (34 weeks of age). Phase three, a finisher phase, would be that period from 25 kg liveweight through to slaughter. Dividing the growing period into phases is simply to signify periods in which the emu requires a change in its dietary nutrient composition to best meet its current level of production. However, until the appropriate nutrient response data are known, the suggestion of a three phase system is only tentative.
Leg disorders
The development of leg deformities has been cited as a common problem in captive bred emus, with clinical signs usually appearing within the first two months of life. A number of different, possibly interrelated conditions may be involved as well as calcium/phosphorus imbalance and methionine deficiency. Maternal nutrition may also be implicated. Dr. Ravindra Bhaskaran of Hindustan Animal Feeds has observed that restricting the time of access to mixed feed to a period of only four hours each day from about 10 to 30 days of age will minimize the incidence of leg disorders in emu chicks.