Minerals from Soil to Animal

#The cows were chewing bones

At Armoedsvlakte, outside Vryburg in what is now North West, cattle died in numbers and the cause was a genuine riddle. Arnold Theiler worked out the answer, and it runs through soil.

The veld there was phosphorus-deficient. Cattle on a phosphorus-deficient pasture develop pica — a depraved appetite — and one of the things they eat is bone. Old carcasses in the veld carry Clostridium botulinum, and the toxin in that bone kills the animal. The disease is lamsiekte. Theiler proved the chain experimentally, showed the grazing was P-deficient, developed a bonemeal prophylaxis, and the work led eventually to a botulism vaccine (Bigalke, JSAVA; Theiler, UP repository). The foundational publications appeared in 1912, 1927 and 1932.

The figure that makes it real: osteophagia may occur in over 80% of cattle grazing a lamsiekte area for most of the year. Not a few strange animals. Most of the herd, most of the time.

That is what a soil chemistry problem looks like by the time it reaches your crush. It arrives as a dead cow with an infectious diagnosis.

#Five to nine months short, every year

The founding South African measurement is Du Toit's work of 1940, and it is more sweeping than most farmers realise. All South African pastures composed mainly or wholly of grasses are phosphorus-deficient for a period ranging from five to nine months of the year — and they never contained enough phosphorus to support gestation or lactation on top of maintenance.

Read that second clause twice. Not "short in a dry year" — short of what a pregnant or lactating animal needs, always, on grass alone. The review of record is De Waal, H.O. (2025) in the South African Journal of Animal Science (full text), the source of every figure below unless stated otherwise.

Severity is regional and the trials mapped it: worst at Armoedsvlakte (Vryburg), minimal at Glen (Bloemfontein), intermediate at Vaalharts, Koopmansfontein, Saratoga and Potchefstroom. Industry sources claim "more than 90% of South African soil is phosphorus deficient" (Voermol) — directionally right, not a statistic for a business plan.

#What South African trials actually measured

The last lesson gave you the industry lick guidance: a summer minimum of 6 g phosphorus per day. Set the trial figures next to it.

Do the arithmetic on the seasonal shape, because it is the point of the table. 16 g/day from September through February — call it 181 days — plus 9 g/day for the remaining 184 days comes to about 4.55 kg of supplementary phosphorus per cow per year. And the demand peak is not even: during the six months when the cow is finishing a pregnancy and then milking, the trial figure is nearly three times the 6 g/day industry summer minimum.

A programme built on "6 g through the summer" is aimed at the minimum, not at the point where De Waal's trials found the money. If your calving is August to October, September to February is your window, and it is the one the trial says pays.

#The salt ceiling, and a question this course cannot answer

De Waal's review carries the other half of the picture. Young sheep on veld required only about 5 g of sodium chloride a day, and higher intakes reduced body mass and wool production. The practical control is to restrict lick intake to less than 80 g NaCl per head per day on a herd basis.

So salt is not free. It is the intake governor from the last lesson, and it is also a nutrient with a ceiling of its own — exceeding it costs production directly, not just money.

Now hold two sourced numbers against each other, because they sit in visible tension and you deserve to be told rather than have it smoothed over. The lick guidance in the previous lesson puts salt at roughly 40% of a sourveld supplement eaten at 400–600 g/head/day. That implies something like 160 to 240 g of salt a day — comfortably above the under-80 g ceiling De Waal reports.

This course cannot resolve that. The two figures come from different sources and were derived for different purposes — one to control over-consumption on sourveld, the other from sheep production trials — so they may simply not be comparable. It is also possible that a lot of South African winter licks do run high on salt.

It is exactly the question to take to a registered animal nutritionist with your own lick label and your own intake records in hand — a far better use of a consultation than asking which brand to buy.

#Notice what the benchmark is measured in

Look again at the status figure in that table, because the units are the teaching point. The South African benchmark of record for phosphorus status is a bone measurement, not a blood test and not a grass sample: rib-bone phosphorus at 140–150 mg P/cm³ is normal, above 150 indicates adequacy, and around 120 mg P/cm³ suggests deficiency.

That is a narrow band — a deficient herd sits perhaps 20 to 30 mg/cm³ below a normal one. Narrow enough that getting the threshold wrong matters: an earlier draft of this course's research put deficiency at "below 100", which would have let a genuinely deficient herd read as adequate. The corrected figure is about 120.

You are not going to be taking rib biopsies, and this course's research did not establish what a routine blood sample would or would not tell you here — so do not assume one settles the question. What the benchmark actually gives you is a reason to route the diagnosis properly rather than eyeball it:

#The map nobody has drawn

Phosphorus is South Africa's signature deficiency, but it is not the only one, and here the country's knowledge runs out in a way farmers should know about.

Historical work mapped what it could: cobalt and copper deficiencies in the old Cape Province, a copper status map for Karoo sheep published by Bath in 1979, iodine deficiency in the Natal Midlands, and selenium excess in parts of Beaufort (Van Ryssen, SASAS; review of mineral imbalances).

Notice that the list contains an excess as well as deficiencies. That one word changes the advice. A farmer in a district where the historical record shows selenium excess, buying a broad-spectrum trace-mineral product because a magazine recommended it, is not being cautious — he is adding to a load the literature already describes as high. Whether that tips into harm on his particular farm is a question for a liver assay through his vet, not for a course and not for a product brochure.

Notice too what the list does not contain: anywhere north of the old Cape and Natal work. This course's research could not find a current, publicly available national trace-mineral deficiency map for South Africa covering copper, cobalt, selenium and iodine. The historical mapping exists. A current one does not appear to be published anywhere a farmer can reach it.

So the honest teaching is a method rather than a map: mineral status is regional, and you find out what yours is by testing, not by reading. The imported advice to give every animal a broad chelated trace-mineral bolus is no substitute for knowing your district's profile — and in a selenium district it is worse than doing nothing.

#What to take back to the farm

The phosphorus chain's real lesson is structural: nutrition and infectious disease are one system, not two. The vet who diagnoses the dead cow and the agronomist who reads the soil report are looking at different ends of the same problem, and on most farms neither is told about the other.

So do the cheap things this week. Walk the veld and look for chewed bones — that costs nothing and it is diagnostic. Remove carcasses. Check that your phosphate programme is aimed at September to February and not just at "summer". And write down the thing you do not know: whether your district has a copper, cobalt, selenium or iodine problem. Nobody has published that answer, but a liver assay through your vet can find it for your farm — the only scale that matters.