The Invisible Toxin That Travels from a Cow's Feed Into Your Milk
Aflatoxin is a naturally occurring mould poison that contaminates cattle feed across India - especially during and after the monsoon. It passes through the cow and into her milk. Here is how it gets there, why it is difficult to detect, and what it means for the milk on your table.
The milk in the packet on your kitchen counter started as grass, grain, and groundnut cake fed to a cow somewhere in rural India. Most of that journey is invisible to the person who buys the milk. One of the things that can go wrong in that journey, quietly & without any visible sign, is aflatoxin contamination.
Aflatoxin is a mycotoxin, a poison produced by Aspergillus flavus and Aspergillus parasiticus, two common moulds that grow on grain, groundnut cake, maize, and stored roughage. The mould itself is sometimes visible as a grey-green fuzz. The toxin it produces never is. A cow can consume contaminated feed for weeks with no obvious signs of illness. The toxin moves through her system and appears in her milk.
In India's dairy sector, the conditions for aflatoxin contamination are not exceptional. They are normal. Hot and humid storage conditions, a feed supply chain with limited quality testing, and heavy reliance on groundnut-based by-products in cattle rations combine to make contamination widespread. Not just in marginal operations, but across the mainstream supply chain.
"A cow can consume aflatoxin-contaminated feed for weeks with no visible signs. The toxin moves through her system and appears in her milk within 24 hours."
FSSAI's limit for aflatoxin M1 in milk sold in India is 0.5 ppb. The European Union's limit is 0.05 ppb - ten times stricter. Pasteurisation and UHT processing do not meaningfully reduce aflatoxin M1 levels. The only point where contamination can be controlled is at the farm, before the milk is ever produced. What the cow eats determines what reaches the consumer.
How Big Is the Problem in India?
These are not edge-case statistics. They describe normal conditions in the supply chains that produce most of the milk consumed in Indian cities. The scale of the problem is why aflatoxin management: testing, sourcing, storage should be a routine farm operation and why the brands that actually do it represent a meaningful quality difference.
Where it enters the supply chainThe Feeds Most Likely to Carry Aflatoxin
Aflatoxin contamination is not uniformly distributed across all cattle feed. It is concentrated in a handful of ingredients. Understanding which ones carries risk helps explain why feed quality and a dairy brand's sourcing transparency matters more than marketing language.
B1 in the Feed, M1 in the Milk
Of the roughly 20 naturally occurring aflatoxins, four affect livestock: B1, B2, G1, and G2. Aflatoxin B1 is the most potent. When a cow ingests B1 through contaminated feed, her liver converts a portion of it into aflatoxin M1, a metabolite that enters the bloodstream, reaches the mammary gland, and is secreted into milk within 12–24 hours of the cow eating the contaminated feed.
This is the direct line between what a cow is fed and what a consumer drinks. It cannot be broken by pasteurisation or processing; only by managing what the animal eats in the first place.
| Type | Found in | Risk to dairy | Feed limit (FSSAI) |
|---|---|---|---|
| B1 | GNC, maize, cottonseed | Highest. Liver damage, immune suppression, milk contamination | 10–20 ppb |
| B2 | Same as B1, co-occurs | Moderate. Additive effect with B1 | Combined total: 20 ppb |
| G1, G2 | Groundnut, spices | Lower but present in mixed rations | Part of combined limit |
| M1 | Milk from exposed cows | Direct human health risk. Appears 12–24 hrs after cow ingests B1 | 0.5 ppb in milk (EU: 0.05 ppb) |
Why Monsoon Season Is the Highest-Risk Window
Aflatoxin does not appear randomly. It follows the weather. Temperature above 25°C and grain moisture above 14% are the two triggers for mould growth on stored feed. Both conditions are normal across peninsular India and the Indo-Gangetic plains for most of the year. The monsoon accelerates contamination. Not just in storage but in the field, as groundnut and maize crops face heat, humidity and insect damage that makes them vulnerable before they are even harvested.
Once groundnut cake or maize is moistened by rain ingress or floor seepage, toxin production can begin within 24–48 hours at 30°C. The mould does not need to be visible. By the time a "musty" odour is noticeable in stored feed, contamination is already significant — and the feed may have been consumed for days before anyone notices.
| Season | Risk level | Why contamination increases |
|---|---|---|
| June–September (Monsoon) | Very High | High humidity in feed stores; field-level infection of kharif crops before harvest |
| October–November (Post-monsoon) | High | Freshly harvested maize and groundnut enters market; storage temperatures still elevated |
| December–February (Winter) | Low–Moderate | Cooler temperatures significantly slow mould growth in stored grain |
| March–May (Pre-monsoon) | Moderate–High | Rising temperatures; kharif-season stock has been in storage longest and is most degraded |
How Aflatoxin Affects the Cow — and Why That Matters for Milk Quality
The liver takes the primary hit. Cows process aflatoxin B1 in the liver and chronic low-level exposure, the kind that happens when contaminated GNC is part of the daily ration, damages liver cells progressively. The effects are rarely dramatic. They look like general underperformance: lower milk yield, animals losing body condition despite adequate feed, increased susceptibility to mastitis and infection.
This matters for milk quality beyond the toxin itself. An animal under chronic aflatoxin stress produces milk with more health events behind it: higher somatic cell counts from subclinical mastitis, stress hormones, and compromised immune function all affect the quality of what ends up in the tank. The M1 contamination is the regulatory concern. The broader picture of animal health is the quality one.
Pasteurisation reduces aflatoxin M1 in milk by at most 10–20%. UHT processing by up to 30%. Neither makes contaminated milk safe or compliant. Cheese and butter concentrate M1 further. The fat fraction carries a higher proportion of whatever was in the raw milk. The only intervention that works is clean feed before the milk is produced.
Why Hydroponic Fodder Is the One Feed with Zero Aflatoxin Risk
Fresh green fodder carries negligible aflatoxin risk because its high moisture content and rapid feed-through time (harvested and fed the same day) do not allow mould to establish. Hydroponic fodder, grown in controlled indoor conditions and fed fresh within 7 days of germination, carries no aflatoxin risk at all. No stored grain, no humidity variation, no mould.
The entire aflatoxin risk in a dairy ration lives in stored dry ingredients: GNC, maize, cottonseed cake. The more of a herd's diet comes from fresh green fodder, the smaller the window through which aflatoxin can enter. A farm that runs year-round hydroponic fodder is structurally reducing its aflatoxin exposure. Not as an incidental benefit but as a direct consequence of removing stored-grain dependence.
A dairy brand whose farms feed documented green fodder year-round, not just in season, is offering a supply chain where the highest-risk ingredient class is structurally reduced. This is the kind of claim that is easy to make and easy to verify: ask whether the farm uses fresh fodder and whether that supply is consistent in July as well as January.
What to take away from this
- Aflatoxin enters the milk supply through contaminated cattle feed (most commonly groundnut cake and stored maize). It is a routine risk on Indian dairy farms, not an exceptional one.
- The toxin travels from feed into milk within 24 hours. It cannot be removed by pasteurisation or any subsequent processing step.
- Contamination risk is highest during and immediately after the monsoon ie June through November, when humidity and temperature create ideal conditions for mould growth.
- India's regulatory limit for aflatoxin M1 in milk is 0.5 ppb. The EU and most export markets require 0.05 ppb ie ten times lower. The milk a consumer buys may be legally compliant but still carry levels that would be unacceptable in stricter markets.
- The only effective control point is feed quality at the farm. Brands that are transparent about what their herds are fed are the ones with nothing to hide on this front.
- Fresh green fodder, particularly hydroponic fodder, eliminates the stored-ingredient risk for that fraction of the diet. It is one of the clearest markers of a supply chain that takes feed quality seriously.
Milk quality starts well before the packet.
Shunya works with dairy farms across India to build the feed infrastructure that keeps aflatoxin out of the supply chain — year-round, not just in the good-weather months.