Butyric acid qualifies as a previously unrecognised vitamin, part 2: differences between ruminants and non-ruminants

(writing in progress)

...continued from https://www.inaturalist.org/journal/milewski/68541-butyric-acid-qualifies-as-a-previously-unrecognised-vitamin-part-1#

In this part of the Post, I examine the milk of bovines (mainly Bos spp., but also Bubalus spp.), the domestic goat (Capra hircus), camels (Camelus spp.), the domestic pig (Sus scrofa), and the horse (Equus caballus).

There is a basic distinction, in gastrointestinal anatomy and physiology, between ruminants and hindgut-fermenting herbivores. Bovines and the goat are ruminants, whereas the domestic pig and the horse are hindgut-fermenters.

Ruminants differ from hindgut-fermenting ungulates in the incidence of butyric acid in milk.

Ruminants' milk contains butyric acid as about 3-5% of the milkfat (based mainly on dairy breeds of Bos taurus).

By contrast, pig's milk does not contain butyric acid (http://fatlab.biology.dal.ca/wp-content/uploads/2013/06/AlstonMillsPigMilk_LPS2000.pdf and http://jn.nutrition.org/content/130/2/234.full), despite the fact that the milkfat percentage is up to 8.5% instead of the < 4% of bovines.

The horse, which is a hindgut-fermenter like the pig, also seems to have milk devoid of butyric acid (http://www.agriculturejournals.cz/publicFiles/10163.pdf). This is despite the fact that horse's milk is the most sugary (as opposed to fatty) in this comparison.

This finding remains open to interpretation.

It may be true that the rumen (forestomach) fermentation, which characterises ruminants, generates butyric acid far more rapidly than does the colonic and caecal fermentation system of suids and equids. However, it does not logically follow that there is a complete absence of butyric acid in the milk of the hindgut-fermenters.

I would have expected a smaller percentage perhaps, but not none. After all, the pig is extremely fatty, and infants of the pig grow extremely rapidly.

My best guess is that the butyric acid in ruminants' milk is there because it is available in quantity from the gut, not because it is required in such quantity by the ruminant infant.

If so, then it is even more fortunate that bovine milk is such a good supplement for butyric acid in humans.

Another way of saying this:
The fact that butter is such a good source of butyric acid is not just a reflection of the fact of pastoralism and domestication of lactating ungulates by humans. Rather, it is a special reflection of the prominence of ruminants in pastoralism.

It is indeed strange to think that if butter were made from pig’s milk (something quite conceivable if pigs were ever milked), then that butter would contain no butyric acid to speak of.

If so, butter, which we take for granted as bovine butter, is a particular gift in terms of its butyric acid. Butyric acid is named after butter, but it is not necessarily typical of butter as such. It is instead, as far as I can see, typical of the butter of Bos, bovines, bovids, and ruminants generally.

Come to think of it, it seems odd that there has been no selective breeding of the pig for dairy breeds. Perhaps the reason is that the milk thus produced would not be competitive with bovine milk in quality (i.e. in terms of butyric acid), regardless of how copious or creamy it might be.

Returning now to ruminants:

The river buffalo (Bubalus bubalis) is widely milked in India and Pakistan, and to a lesser extent in e.g. Turkey, Italy, and Brazil. Its milk is similar to that of Bos in having butyric acid as 4.1% of the butterfat. This means that, as in the domestic bost, this milk has about one part per thousand of butyric acid in its fresh condition.

I have also confirmed that ghee, which is often made from the milk of the river buffalo in the Hindu tradition, contains the same value, namely butyric acid as ca 4% of the lipids.

Goat's milk is slightly richer in butyric acid than bovine milk:

I have already established that bovine milk contains about one part per thousand of butyric acid.

This is confirmed in http://cdn.intechopen.com/pdfs-wm/39464.pdf, with a precise value of 1.1 parts per thousand.

However, please note that goat's milk is even richer in butyric acid than bovine milk, with a value of 1.3 parts per thousand. The corresponding values for pig's and horse's milk are, as far as I can ascertain, zero.

Butyric acid as proportion of milk:

See http://www.jbc.org/content/154/1/255.full.pdf.

In human milk, the proportion of fatty acids contributed by butyric acid seems to be 0.4%. This is about an order of magnitude less than that in bovine milk.

This suggests that the bovine animal puts a lot of butyric acid in its milk partly because it generates a lot of butyric acid via microbes in its rumen.

If it is true that butyric acid functions as an essential fatty acid in the adult human, the implication is that bovine milk is a far richer source of this substance than human milk would be.

The > 3% of milkfat contributed by butyric acid in the bovine exceeds the <1% of milkfat contributed by butyric acid in the human for reasons other than the greater rate of synthesis of butyric acid in the gut of the bovine.

My suggestion for this greater concentration of butyric acid in bovine than human would be the far greater rate of growth of the bovine infant than the human infant. Human babies grow extremely slowly for mammals.

Fat (made of fatty acids) constitutes 3.5% of bovine milk. Of this fat, about 3% is butyric acid.

This means that butyric acid constitutes about 3% of 3% of milk. This works out to ca 0.1% of milk, = about one part per thousand. In other words one-tenth of one percent of bovine milk is butyric acid.

When one drinks a litre of fresh bovine milk, one is drinking one ml of butyric acid. In terms of mass instead of volume: a litre of milk contains ca 1000 grams, of which < 1 gram of butyric acid.

What is remarkable is that, even though one only consumes < 1g of butyric acid in a whole litre of milk, this is still way more than one would be getting from other fatty foods, such as bacon, avocado, peanut butter, margarine, etc., all of which contain zero butyric acid as far as I know.

Constancy of butyric acid content of bovine milk on different diets:

Bovine milk is exceptionally complex in its fatty acid content.

However, the butyric acid content of bovine milk is remarkably predictable at about 3.5%.

Butyric acid has the formula 4: 0. It has four atoms of carbon and no unsaturated bonds. I am still searching for a paper that states clearly that all the butyric acid in milk comes from the contents of the gut, as opposed to being synthesised in the mammary glands themselves.

One apparent anomaly is that the milk of camels is poor in butyric acid (https://www.dairy-journal.org/articles/dst/pdf/2008/03/dst0732.pdf), despite these artiodactyls being similar to ruminants in their gastrointestinal anatomy and physiology.

The distinction between ruminants and hindgut-fermenters has implications for seed-dispersal syndromes.

In particular, I suspect that the wild ancestor of Ceratonia siliqua (https://www.inaturalist.org/taxa/82742-Ceratonia-siliqua) was adapted to dispersal by wild asses.

Catatonia siliqua is a caesalp leguminous tree that produces carobs, viz. legume pods with thickened, sugary pod-walls when ripe. This ripe fruit-pulp contains isobutyric acid (http://www.theodora.com/encyclopedia/b2/butyric_acid.html). Furthermore, it certainly has a cheesy odour, consistent with richness in butyric acid.

The fruit category called carobs occurs in various leaves of leguminous plants, including Vachellia and Cassia. All carobs have relatively dry fruit-pulp when ripe, and are adapted for dispersal and sowing of seeds by ungulates, as opposed to birds or primates. However, some species (e.g. Vachellia nilotica) seem to be oriented more towards ruminants, and others more towards perissodactyls.

I suspect that spp. of carobs designed mainly for ruminants tend to lack butyric acid, whereas those designed mainly for non-ruminants tend to contain this substance.

I am unsure how butyric acid and isobutyric acid differ functionally. However, isobutyric acid is an isomer of butyric acid, i.e. it shares the same chemical formula (C4H8O2), but with a different molecular configuration.

(writing in progress)

Publicado el julio 27, 2022 04:50 TARDE por milewski