Give a dog a bone!

There are several reasons for giving your dog a bone. They provide essential nutrition but gnawing a bone also releases calming endorphins that promote a sense of well-being (resulting in a happy dog). Bones also clean their teeth into the bargain. This article is not about the behavioural or psychological aspects of feeding bones but concentrates on the nutritional benefits. There is confusion around this latter point with some commentators talking about a 10-20% bone content and others focusing on the calcium content of particular recipes which will usually be 1% or less. Firstly a chicken leg, wing or carcass is 70% water, 20% meat and 10% bone. Therefore 100g of chicken leg contains around 10g of bone.

Bone is living tissue and is a complex matrix. Calcified bone is approximately 25% collagen, a protein that provides the bone’s elasticity, and c70% minerals, the major one being calcium hydroxyapatite, a relatively hard, lightweight inorganic ‘composite’ material. So 10g of bone contains up to 7g of calcium hydroxyapatite. The other 5% comprises bound water, minerals and trace elements. Calcium hydroxyapatite has the chemical formula Ca10(PO4)6(OH)2 and as such it is 40% calcium. So up to 2.8g of calcium in 100g of chicken wing or 1.1 g in 40g. What this maths means is that a dog will require about 3.6g of calcified bone in order to ingest 1g of calcium.

FEDIAF (The European Pet Food Industry) guidelines recommend a calcium intake of between 1.25g and 6.25g per 1,000kcal of Metabolizable Energy (ME). The FEDIAF guidelines are for processed food and are of limited applicability to raw feeders but they do provide a starting point for discussion. The reason they express the required amount by reference to ME is because foods differ significantly in so called ‘energy density’ (ie how many calories per Kg). Complete raw foods will typically have an energy density of around 1,500kcals per Kg and so the FEDIAF guidelines in essence are recommending between 1.25 and 6.25g of calcium in approximately 670g of food or between 2 and 9g per Kg (0.2 to 0.9%). 670g of food is the daily requirement of a medium sized (say 20Kg) dog. More than this isn’t a major problem for adult dogs as they can regulate their calcium intake.

Dog food is not required to disclose its calcium content nor the all-important calcium to phosphorous ratio but some producers do disclose one or both. Good quality raw foods are high in meat content and hence high in phosphorous, typically containing 0.5 to 0.6% phosphorous. Raw food needs bone in order to achieve the ideal calcium to phosphorous ratio (there must be more calcium than phosphorous) and typically have a calcium content of around 1%. This will provide about 6g of calcium per 1,000kcals – at the top end of the FEDIAF guidelines and slightly less than the typical Prey Model diet. In reality a calcium content of between 0.5% and 1.5% should be fine as long as the important Ca:P ratio is achieved. If the calcium content or Ca:P ration isn’t disclosed on the label you can always ask the manufacturer.