Emus - nutritional requirements for breeding

Digestive system

Anatomical studies have revealed that the emu's digestive system comprises of 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 do not have a distinct crop. The proventriculus, however, is quite distensible and possibly could serve as an organ for food storage. The total length of the emu's digestive tract is relative to its live weight and 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 nature of the item ingested. Plant matter will take an average of five to six hours; intact wheat grains will take 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.

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Nutritional requirements

Emus, like other birds, need essential nutrients to grow and reproduce.

Energy

Ingredients high in carbohydrates and/or fats are energy sources and can include cereal grains and full-fat soyabean meal.

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. There are more than 20 amino acids of which about 11 cannot be manufactured by the emu and must therefore be present in their 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 is 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. Some fibre is necessary to promote healthy gut function but in nutritional terms its value is low.

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Supplying nutrient requirements

The ability to supply the nutritional requirements of emus depends on the feed composition, that is, the concentrations of the essential nutrients in the feed and the amount of feed consumed by the birds. When all the emu's diet comprises a compounded feed, precise control can be had over their intake of nutrients. When a proportion of their diet is derived from range, their quantitative intake of available nutrients is less predictable.

As emus approach sexual maturity an increasing proportion of their live-weight gain is body fat. The reproductive fitness of female emus is enhanced by ensuring only a very limited gain in body fat beyond 12 months of age. This may be achieved by giving the birds unrestricted access to a maintenance diet (Table 1) supplemented with lucerne pellets, hay or pasture. Close monitoring of live-weight gain together with experimental information on body composition may suggest a need to restrict the intake of the maintenance diet during this period. However, feed restriction may not be necessary, as O´Malley (1991) reports, emus in their second year exhibit a marked seasonal fluctuation in feed intake. He observed feed intake to fall by as much as 40% to 50% in summer then rise slowly during autumn and winter before increasing more sharply in late winter and spring. This reduction in appetite with the onset of hot weather seems to be more than a reduced maintenance requirement for dietary energy because birds become stressed during this period with some losing weight.

As the mature breeding female approaches the egg-laying season she will require a higher plane of nutrition to meet her needs for egg formation compared with the earlier maintenance period. The time taken for an egg to develop is about five weeks for the emu and it is recommended that females be switched to a breeder diet six weeks prior to their first egg being laid. A high plane of nutrition is required also by breeding males to ensure they attain good fertility and to increase their body reserves prior to natural incubation. A suggested emu-breeder diet is given below (Table 1). This diet should contain a comprehensive poultry breeder vitamin and mineral premix.

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For mature breeders it is necessary to satisfy only their maintenance requirements during their out-of-breeding season.

Examples of diets which meet the specifications given above are presented in Table 2. These are given as a guide only and do not necessarily represent the cheapest combination of ingredients available.

This information is based on DPI&F research from the early 1990s.

References

McDonald, MW (1991). Ostrich nutrition - an international review. Australasian Poultry, 2(5): 14-15.

O'Malley, P (1991). Emu field day talk. West Australian Department of Agriculture.