LSU, SSU, GU, BU — and the Frame-Size Trap

#You can change your stocking rate without buying an animal

Sell thirty Nguni cows. Buy thirty Simmentaler cows at exactly the same weight. Same head count, same kilograms of cattle standing on the same veld.

You have just raised your grazing pressure by about a fifth.

The ARC's own figures say a 450 kg small-frame cow with a calf at foot is 1.32 large stock units, and a 450 kg large-frame cow is 1.60 — a 21% jump at identical liveweight. Dry matter intake moves with it: 12 kg DM/day against 15 kg DM/day, a 25% difference (Mokolobate, Scholtz & Calitz, ARC, 2017).

Nobody sent you a letter about it. The camp gate did not move. But the veld now has to grow a fifth more grass for the same herd, and it will not.

That is why this module starts with arithmetic. Every number in the rest of this course — grazing days, rest periods, destocking triggers, the legal ceiling on your farm — is computed from a single total. If the total is wrong, everything downstream is decoration.

#What one LSU actually is

South Africa has two working definitions of the LSU and they are the same animal described two ways.

The production definition — the one the grazing capacity map is built on — is an animal of 450 kg gaining 0.5 kg per day on forage of 55% digestible energy. That definition traces to Meissner and to Trollope, Trollope & Bosch (1990), and it is the basis the department states in the background document to the long-term grazing capacity map.

The intake definition is the same animal from the feed side: 75 MJ of metabolisable energy per day (ARC, 2017), which the South African animal-science literature expresses as 9 kg of dry matter a day — exactly 2% of 450 kg (Jordaan et al. 2021). Energy is also the currency the wildlife literature uses, because you cannot compare a kudu to an ox on liveweight but you can compare them on megajoules.

You will hear the 9 kg rounded up to 10. If you round, say that you are rounding. And use the figure to sanity-check a fodder budget, not as a constant: the ARC's own frame-size figures — 12 and 15 kg DM/day for a cow with a calf at foot — show how far real intake moves off the round number once you name the animal's frame and its physiological stage.

#The frame-size trap

The trap is that LSU is not linear in body weight, and it is not the same at the same weight.

Two 450 kg cows, both with a calf at foot, both grazing the same camp. The small-framed one is 1.32 LSU. The large-framed one is 1.60 LSU. She is not heavier. She is built to run a bigger engine, and she is running it on your grass.

The ARC groups the breeds:

Two precision points, and they matter more than they look.

Say which physiological stage you are converting. The 1.32 and 1.60 figures are for a cow with a calf at foot, not a dry cow. The ARC publishes separate regression equations for lactating cows, replacement heifers, weaners and bulls. "A cow is 1.32 LSU" is not a fact; "a small-frame cow with a calf at foot at 450 kg is 1.32 LSU" is.

Say which number you took. The ARC paper's narrative text gives 1.60 for the 450 kg large-frame cow, but its own Table 2 gives 1.66 at that weight. Work from the narrative and the swap costs you 21%; work from the table and it costs you 26%. Either is defensible. Quietly mixing them is not.

#Small stock: the factors South Africa actually publishes

For sheep, the Western Cape Department of Agriculture uses the Meissner et al. (1983) class factors, published in the Elsenburg veld management infopaks:

Notice that a ewe with a lamb costs a third more than a dry ewe. Lambing season is not a neutral event on your grazing ledger — it is a step change in demand that arrives at a fixed date every year.

You will also hear "1 LSU equals 6 small stock units", sometimes justified with energy figures of 124.9 against 12.5 MJ ME per day. Treat that as a rough conversion only. The research behind this course could not trace that ratio or those energy figures to a primary South African source. The class factors above are sourced, they are what the department itself uses, and they happen to imply roughly six to seven wool ewes per LSU anyway — so use the factors and skip the shortcut.

#Game: two ledgers, not one

If you have wildlife on the place — resident, fenced or wandering in — you are running two accounts at once, and the department's map only tracks one of them.

Shepstone and co-workers (2025), in the South African Journal of Animal Science, set the wildlife units on metabolisable energy:

• LSU = 75 MJ ME/day (the 450 kg steer)
• WHU, the Wild Herbivore Unit = 29.71 MJ ME/day
• GU, the Grazer Unit = a mature 180 kg blue wildebeest
• BU, the Browser Unit = a mature 180 kg greater kudu

Read those last two again. Both reference animals weigh 180 kg. The units do not differ by body mass at all — they differ by feeding class. A GU spends grass. A BU spends browse. They are two currencies for two resources, and a farm can be broke in one while rich in the other.

Their worked example makes the point better than any diagram. A Cape eland at 460 kg is 1.02 LSU, 2.57 WHU, and 1.28 GU and 1.28 BU at the same time — because a mixed feeder draws on both ledgers simultaneously. In their intensive-breeding scenario the herd ended at 234 LSU against a 200 LSU grazing ceiling while still sitting inside the browse ceiling: overstocked on grass and understocked on browse, on the same property, in the same season. The correct response was a species-selective destock, not a blanket one. A single-ledger farmer would have sold the wrong animals.

This matters even if you never buy a head of game, because the department's map is a grazing map. It states plainly that tree crown cover was not incorporated and that browsing capacity is not included at all (DALRRD). On bush-encroached veld you have a browse resource the map cannot see, and a grass resource the map is overstating.

#The gap: goats

Here is where the arithmetic runs out, and you should know it before you need it.

There is no authoritative South African goat-to-LSU or goat-to-SSU conversion factor. The research behind this course searched for one and did not find it at any level of authority that would justify printing it. So this course does not print one.

The law does hand you a number — CARA's Regulation 11 Table 2 lists a Boer goat ewe at 0,17 and an Angora ewe at 0,11 (CARA regulations) — and Module 3's next lesson deals with that table properly. But understand what that number is and is not. It is a legal accounting factor, used to work out whether your total animal count sits inside a ceiling derived from a grazing capacity map that explicitly excludes browse. It tells you how the goat counts against the department's ledger. It does not tell you how many goats your woody layer can feed, because nobody has drawn that map.

Which is why goats are not sized on ha/LSU in this course at all. They are sized on a browse audit of the actual woody and forb resource — the method is in Module 12. On Highveld grassland with almost no woody layer, that audit will usually tell you the goats are competing directly for grass, which is the opposite of the reason most people buy them.

#Do the sum on your own place

Take a mixed Highveld operation:

• 30 small-frame cows with calves at 450 kg → 30 × 1.32 = 39.6 LSU
• 60 wool ewes with lambs → 60 × 0.20 = 12.0 LSU
• 60 lambs → 60 × 0.10 = 6.0 LSU
• 2 rams → 2 × 0.19 = 0.38 LSU

Total: 57.98 LSU.

Now run the same farm on large-frame cows at the identical 450 kg: 30 × 1.60 = 48 LSU, and the total becomes 66.38 LSU. Same head count. Same kilograms of animal. A 14% larger claim on the veld, and about 8.4 LSU of it arrived from a breed decision that felt like a marketing choice.

That is the whole point of a common currency. Head count hides this. Kilograms hide this. Only the ledger shows it.

Before the next lesson, write down your own total — every class, every factor, with the source of each factor beside it. You will need that number for the legal ceiling in the next lesson, and for the grazing-day balance in the one after that. If you cannot produce it in ten minutes, that is itself the finding.