Blog · FBS · Supply · November 2026 · 6 min read

US Cattle Herd Rebuilding: Why FBS Gets Tighter Before It Gets Better

The US cattle herd has hit bottom. That sounds like good news for anyone buying fetal bovine serum. It is not — at least not yet. When ranchers rebuild their herds, they keep exactly the animals that FBS comes from.

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The Numbers: A Herd at a 75-Year Low

The latest USDA data confirm what FBS buyers have felt for two years: the US cattle herd is smaller than at any time in living memory — and the beef cow herd, the main source of cull cows, is still shrinking.

Indicator	Latest figure	Context
Total cattle and calves (1 Jan 2026)	86.2 million	Lowest since 1951
Beef cows (1 Jan 2026)	27.6 million	Lowest since 1961
2025 calf crop	32.9 million	Smallest since 1941
Beef cows (1 Jul 2026)	28.45 million, −0.7% year on year	Still declining
Beef replacement heifers (1 Jul 2026)	3.8 million, +2.7% year on year	First sign of herd rebuilding
Beef cow slaughter (Jan–Aug 2026)	−14% year on year	On pace for a record low

Sources: USDA NASS Cattle reports, January and July 2026; USDA slaughter data as analysed by the University of Kentucky. Full list at the end of this article.

Where FBS Actually Comes From

FBS is collected from the fetuses of pregnant cows and heifers at slaughter. It is a by-product: no animal is slaughtered for its serum, and for meat packers it is a minor revenue stream. The volume of FBS therefore depends on one thing — how many pregnant animals reach the abattoir.

According to a 2026 study in Translational Animal Science (Jungbluth, Brorsen and Peel), those animals come mainly from two groups: cull dairy cows, which are often pregnant when culled, and cull beef cows. Pregnant feedlot heifers are a minor source. On average, one fetal calf yields only about 0.4 litres of serum, and collection peaks in spring and autumn, when calves are closer to term.

Why Rebuilding Makes FBS Tighter — Not Looser

Intuitively, a herd that has stopped shrinking should mean more FBS. In practice, the first years of a rebuild do the opposite, for three reasons:

1. Heifers stay on the ranch

A heifer retained for breeding becomes a cow instead of going to the feedlot or the abattoir. USDA counted 2.7% more beef replacement heifers in July 2026 than a year earlier. Every retained heifer is one animal fewer in the slaughter pipeline this year.

2. Fewer cows are culled

With calf prices at record levels, a bred cow is worth more alive than at slaughter. Beef cow slaughter fell 14% in the first eight months of 2026 — and cow slaughter is the single largest driver of fetal serum volume.

3. Pregnant dairy cows calve first

Dairy-beef crossbred calves now fetch high prices. As a result, dairies increasingly keep pregnant cull cows until they have calved instead of sending them to slaughter while pregnant, as the 2026 study notes.

The bottom line: the cattle cycle works against FBS buyers twice — first during liquidation, when there are fewer animals, and then during rebuilding, when fewer pregnant animals are slaughtered. USDA estimates the 2026 calf crop at 32.5 million head, 1.5% smaller again. Analysts expect tight cattle supplies at least through 2027; a recovery in fetal serum volumes would follow only after that.

Will Mexican Cattle Imports Help?

In 2025 the US suspended live cattle imports from Mexico because of the New World screwworm. In August 2026, USDA began a phased reopening through the port of Douglas, Arizona, initially limited to around 700 head per day with screening of every animal.

Imported cattle add to beef supply, but they are mostly young feeder steers and heifers bound for feedlots — not pregnant cows. For FBS volumes, the effect is marginal.

What This Means for US-Origin FBS

Many validated processes and regulatory files specify US-origin FBS. Those users cannot simply switch, so demand stays concentrated on a volume that is still shrinking. In practice, buyers should expect allocations, fewer large homogeneous lots and longer lead times for US-origin material.

Origin	What to expect	Key consideration
USA	Tightest availability, allocations likely	Reserve qualified lots early; plan volume for the full project
South America	Larger volumes available	Check TSE/BSE documentation requirements — see our South American origin guide
Australia	Smaller volumes, premium pricing	Strong regulatory acceptance; lots sell out quickly

Four Steps for Buyers and QA Teams

1. Check what your specification really requires

Does your process or regulatory file require US origin — or only a defined quality and an approved origin? Many research applications are not tied to a specific country.

2. Reserve your qualified lot

Once a lot is qualified, reserve it for the whole project. With SeamlessBio batch reservation, lots can be held for up to 36 months with free storage and no prepayment.

3. Qualify a second origin now

Run the comparability study while there is no time pressure — not when your current lot runs out. Free test samples make this low-risk.

4. Plan volume over the project lifetime

Order planning per purchase order no longer works in a constrained market. Estimate total demand for the project period and secure it in one lot. Our FBS procurement guide explains how.

For the broader market picture, read FBS Supply Shortage 2026, or see all biological raw materials we supply.

Secure Your FBS Lot Before the Next Allocation Round

SeamlessBio supplies FBS of US, South American and Australian origin — processed and tested in Passau, Germany, with CoA and TSE/BSE documentation. Test before you commit.

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Frequently Asked Questions

Why is the US cattle herd so small?

Several years of drought, high feed costs and strong cattle prices led ranchers to sell down their herds. On 1 January 2026, USDA counted 86.2 million cattle and calves — the lowest number since 1951.

Does a growing herd mean more FBS?

Not at first. During rebuilding, ranchers retain heifers and cull fewer cows, so fewer pregnant animals reach slaughter. FBS volumes typically recover only once the larger herd starts culling again.

When will US FBS supply improve?

USDA data from July 2026 show heifer retention at a level that roughly holds cow numbers steady rather than growing them. Analysts expect tight cattle supplies at least through 2027, so a recovery of US fetal serum volumes is unlikely before then.

Can I switch from US-origin FBS to another origin?

Technically yes. For regulated processes you will need a comparability study and possibly a change to your regulatory documentation. Research users can often switch more easily. Free test samples help you qualify a second origin without risk.

Does SeamlessBio still supply US-origin FBS?

Yes. We supply US-origin FBS alongside South American and Australian origin, and we can reserve a qualified lot for up to 36 months.

Sources: USDA NASS, Cattle report, 30 January 2026 · USDA NASS, Cattle report, 24 July 2026 · K. Burdine, University of Kentucky, cattle slaughter trends 2026 · Jungbluth, Brorsen & Peel (2026), Production, pricing, and incentives in the fetal bovine serum market, Translational Animal Science · AP, US to begin lifting suspension of Mexican cattle imports, July 2026.