MAMMALIAN MILK SHOULD NOT BE FED TO BIRDS
Tuesday, 10th December 2013
In those days some canary breeders professed that it was this unusual diet that gave their birds an edge over others. There is no excuse these days for not trying to understand what is good for our birds and what is not. Just a bit of reading of modern scientific publications and trying to learn more about avian biology and even a bit of common sense will tell you that milk is not beneficial to birds.
Perhaps for a start we should first consider the basic composition of normal full fat cow’s milk; 88% water, Protein 3%, Fat 4%, Carbohydrate 5% in the form of sugars (lactose)( Source: Wikipedia <http://en.wikipedia.org/wiki/Milk>). Now the less enlightened may say that this is a good source of easily absorbable well-balanced nutrition but fails to note that its prime purpose is to feed and maintain mammals in the early years of their lives. Even humans develop milk intolerance as they grow older and leave their mother’s breasts to obtain their nutrition from other foods. However should we even be discussing the effects of milk on adult mammals when our concern is for birds? If birds had evolved to feed their young on milk similar to mammals, they would also have evolved with the wherewithal to provide it. They obviously have not as appendages would add to their body mass and inhibit flight.
As most cow’s milk today is homogenized the basic constituents are normally well mixed and domestically inseparable and if fed as such to say a small bird with a body weight of 30g it would need to consume its own volume of milk just to take in 1.7g of lactose. But being realistic if the bird were offered a portion of bread and cow’s milk each day, it would then consume only a small fraction of a gram of lactose; perhaps less than a beakful. Assuming the bird cannot digest lactose this substance may pass straight through the body or as is often the case, show up as diarrhoea. Any benefit that may exist could come directly from the bread but there is no proof at all that the milk is beneficial.
While there is evidence that bread and milk was fed to captive cage birds as early as 1759 there is no corresponding evidence that it was beneficial. This myth has been propagated in numerous non-scientific publications ever since and we should be very wary of such unwarranted publicity. On a parallel train of thought we also know that tobacco was introduced into Europe around 1520 but it was only in the 1950’s, some 430 years later, that it had been scientifically proven as a major health hazard for humans.
But why should we feed mammalian milk to birds at all? Birds are NOT mammals and have evolved to survive for millions of years without it or anything like it. Pregnant female mammals provide sustenance to their unborn young via the placenta and the colostrum needed by the young in the first few days of their lives becomes available shortly before birth. It contains antibodies and immunoglobulins, which help protect newborns as they come into a world laden with bacteria and viruses. Then the mother produces her milk, which is the complete nourishment needed by the young for some time after birth. Mammals produce the enzyme – lactase, specifically needed to digest lactose (milk sugars).
Birds, however, are a completely different group of animals, hatching out of eggs and as bird embryos are enclosed in an egg during incubation the egg must contain all the nutrients and fluids necessary to sustain the bird until it hatches. It is through regurgitation of their food to feed their young during the first few days of their lives that parents pass on those substances needed for the young to be protected against viruses and bacteria. Some species such as the doves and pigeons produce a substance known as ‘crop milk’ but this misnomer is confusing, describing just the appearance of the soft, creamy lining of the crop that is regurgitated directly by the parents into the young squab’s gullets. Although rich in fats and proteins it contains no milk sugars (lactose), calcium or carbohydrate as is found in mammalian milk.
Turning to the scientific proof we should first consider the most likely sources and these are where humans are very dependent on birds – poultry science which requires a thorough understanding of avian nutrition. A key publication on this subject is Kirk C. Klasing’s book Comparative Avian Nutrition (CAB International 2000) which uniquely covers all aspects of our current knowledge. For any birdkeeper with an academic mindset wishing to dig deeply into avian physiology, ecology and biology this book is highly recommended. Here you will find the physical and biochemical processes of digestion and the metabolic functions of nutrients essential to understanding why lactose is thought to be indigestible in birds. To quote “The spectrum of enzyme activities in the brush border of the small intestine of birds is similar to that in mammals and includes phosphotases, disaccharidases and peptidases. A notable difference is that lactase has yet to be found in the intestines of birds. Unlike mammals, the avian enterocytes do not have lactose activity. In most birds, this results in lactose intolerance when fed milk or other lactose-containing foods”.
Cow's milk products are a different issue particularly where the fats have been separated out. Small quantities of cheese may appear harmless and the butter left on bread scraps put out for the birds in winter may be a useful source of energy. The best advice for birdkeepers is to avoid giving any form of milk to your birds as it can lead to illness and perhaps death.
Written by Tony Tilford