Feeding bran and how to balance the CA:P ratio with limestone flour
Wheat bran was once a very common feed ingredient in the UK and, although it seems to have become less popular in recent years, in many parts of the world it does seem to still be used a lot and can be a useful feed ingredient.
The starch content is, however, high (typical 23%; 230g/kg) a moderate sugar (typical 7%; 70g/kg) so not suitable for EMS/Lamintic horses or ponies. Wheat bran is a good source of protein (typical 17%; 170g/kg).
So wheat bran can be good and bad. It can upset the calcium:phosphorus ratio which can be bad for bone, especially in youngstock or endurance horses or horses in hard work, and once-a-week bran mashes should be avoided as this upsets the hindgut microbiome! If you feed wheat bran, feed the same amount every day.
IF YOU WANT THE SHORT ANSWER SCROLL TO THE BOTTOM, KEY POINTS!
One of the main issues with feeding wheat bran is the low calcium (Ca) to phosphorous (P) ratio. Normally we are looking to have a whole diet ratio of at least 2:1 (Ca:P).
The problem with wheat bran is the ratio of Ca:P is 1:11! i.e. there is 11x more P in wheat bran than Ca. Wheat bran typically has around 11g P per kg whilst the amount of Ca is only 1g per kg.
So we need to balance the high P and low Ca by adding in a source of calcium and the most common and cost-effective is limestone flour (Calcium Carbonate). We want to aim for twice as much calcium as phosphorous – a 2:1 Ca:P ratio. But how much limestone flour do we need to add?
1kg of wheat bran has 11g phosphorus and 1g calcium. To get twice as much calcium we need to add 2 x 11g P = 22g, minus the 1g of Ca that’s already in the wheat bran. So per kg of wheat bran we need to add 21g of calcium.
Limestone flour is 40% calcium. So 40g calcium per 100g. We want 21g of calcium, so adding 50g of limestone flour a day would be close (20g). But we usually feed by volume not weight e.g. 25ml scoops.
Limestone flour has a density of around 1.1g/ml, so if we fed 2 x 25ml scoops a day (50ml) that would be equivalent to 1.1*50 = 55g limestone = 22g calcium!
THE SHORT ANSWER
A 2.7 litre Stubbs scoop holds ~540g wheat bran (density of wheat bran ~0.2g/ml)
If you are feeding wheat bran, for every kg you feed you should add at least 2 x 25ml (55g) per day of limestone flour.
If you are feeding wheat bran, for every Stubbs scoop you feed you should add at least 1 x 25ml (27.5g) per day of limestone flour.
Most commonly fed brans tend to be high in phosphorus (P) and low in calcium (P). Below is a table with the amounts of limestone flour to add per kg of common brans either as g or level 25ml scoops! Of course ideally the whole diet should be balanced for Ca:P with a ratio of at least 2:1!