Hi, P09. I’ll leave the more technical stuff to the knowledgeable members – but look if it this way:
any feed will work pretty much okay for a while. The birds wouldn’t starve. I think it’s a question of long-ish-term nutritional balance, which takes you back to reading about the contents of the feeds.
Try ‘Swarbrick Emu Husbandry Guidelines.’ Yes, it’s about emus; but it will introduce you to the idea that you need to be able to go to the feed-store and say, ‘Hi, do you have a feed that’s high in X, with some Y and Z supplements?’ I’m a novice gardener, and I’m learning similar things: you can pile Good Stuff A, B, and C onto your pea plants, and . . . nothing much happens. Then, if put Good Stuff Z on them, they thrive.
How much grass can an ostrich eat? Well, think about loading a pickup truck with a pair of tweezers. That is, they must spend hours and hours grazing every day when they are in a natural environment – emus do. I think that if the birds have an elegant sufficiency of space, and that space generally has a good coverage of grass, then the ostriches will be getting enough grass.
If I may:
I suspect that ‘grass’ is not quite simply the answer. In the wild, ostriches and emus eat a wide range of foods: berries, seeds, flowers, and grass – and we can argue later over whether they also eat snakes, bugs, insects, etc.
Have about this for an ‘equation’: the birds need (a) certain nutritious ‘inputs,’ and (b) they need something – like grass – as a ‘vehicle’ to get the inputs in one end and out the other. Humans are the same: you could probably get enough nutrition from pills, but I think you’d be in trouble after a while if you only ate pills. Sneaking the pills into a wholemeal cheese-and-tomato sandwich would be a great idea.
So, Wild Bird: has evolved in its environment. Eats certain things in certain quantities at certain times. Result: healthy bird
Pet Bird: has evolved with same needs, but isn’t in a natural environment. Grass – roughage, the sandwich – is the ‘primary vehicle’ of those needs. (Swarbrick notes that the emus where she studied got a kilo of fresh silverbeet a day as roughage.) So, grass is good and necessary; but so are the things that the birds usually also get from the seeds and berries. Determine what those things are. Supply them to the birds. Result: healthy bird.
I note that my emus love every non-grass thing they can get. For example, they spend hours foraging (just like giant chickens!) under the lilly pilly tree for lilly pilly berries; and in Spring, I have the hilarious sight of seeing vicious dinosaur girlie bird come up to me with a yellow flower hanging from the corner of her mouth.