Different bird owners do give their birds cod liver oil here are examples of what others do on our forums and why.

Member Name: Daz I mix 5ml per 500gms of seed. I leave it 24 hours before feeding it to the birds

Member Name: macka  It's a good addive,but needs to be used with care. I use it in the breeding boxes,to feed the chicks. I mix 10mls to 1 kilo of seed & leave it stand over night & feed the next day. If you put to much oil in the seed,it will turn sour. With just 5 budgies I wouldn't feed it more then 2 times a week. It can make the budgies to fat. I myself wouldn't feed it to my flighted bird for that reason.

Member Name:  Paul29  don't use cod liver oil.....however I do use olive oil and I use it everyday of the year....I have found that the seed we get here in Perth is always very dry....the olive oil puts back the moisture with more protein and helps hens with there egg laying.....

Member Name: Kaz  put a few drops of codliver oil and wheatgerm oil into the softfood I prepare for my budgies. In talking with a show breeder once he told me to use cod liver oil and wheatgerm oil ....as a seasoned show breeder had taught him. He swore by the difference it made to the birds.

Member Name: feathers My breeding room birds get seed soaked in cod liver oil and wheatgerm oil. The cod liver oil supplies vitamin D which is required for calcium uptake in birds. This is why it is so commonly used for breeding birds. My breeding room uses 500ml of seed per day, to which I add 4 ml cod liver oil and 1 ml wheatgerm oil, which is left to soak for 24 hours.

Member Name: splat  use 5ml of cod liver oil to my breeding birds because like feathers said it is a Vit D plus A few breeders have told me that while using cod liver oil you will rarely get a bird egg bound. The egg bound thing is my main reason for using it.  When my son had his horse while living in Bendigo I would also give the horse cod liver oil for the Vitamins plus I think it helped his coat nice and shiny the horse always looked very healthy as do my birds