After the autumn harvest, new-season corn gradually comes onto the market. It costs less than old-crop corn, so many pig farms switch to it without a second thought. But every year around this time, some farms run into trouble: pigs get diarrhea, grow slowly, sows miscarry, and antibody levels fail to rise after vaccination. After checking everything, the problem turns out to be in this “new feed.”
It’s not that new-season corn can’t be used; you just need to know how to use it. This article explains the two pitfalls of new-season corn, the harm caused by mold, and a practical way to use it.
When new-season corn has just been harvested, its moisture content is generally high. Drying it first is the first step.
One: New-season corn has two pitfalls: high moisture content and high levels of resistant starch
The first pitfall is moisture. Newly harvested corn generally has a moisture content of 15%–20% in North China, and can reach 20%–30% in Northeast China and Inner Mongolia. The safe moisture requirement for feed corn is below 14%; in practice, it is best to keep it within 14%–15%.
When moisture is high, problems follow: the energy concentration is diluted and the protein proportion rises relatively, resulting in nutritional imbalance; pepsin cannot digest the suddenly increased amount of protein, which can easily cause indigestion and nutritional diarrhea; and high-moisture corn respires actively, making it especially prone to heating and mold, so it cannot be stored for long.
The second pitfall is resistant starch. Corn is a crop that continues to mature after harvest, and the proportion of resistant starch is highest when it has just been harvested, accounting for around 10% of the total starch. This cannot be digested in the small intestine, so it is effectively wasted; once it reaches the hindgut, bacteria such as E. coli can ferment and use it, producing toxins and causing loose stools. It also slows the passage of digesta, leaving pigs with a sustained feeling of fullness and preventing their feed intake from increasing.
That is why many pig farms find that after switching to new-crop corn, pigs eat plenty but do not gain weight and are prone to diarrhea. The root cause lies in these two issues.
Resistant starch gradually converts during storage. Generally, after being stored for 5–6 weeks (about one and a half months), it decreases. This is why “new corn should be aged for a while before feeding.”
II. More troublesome than moisture: mold
Many people think corn becomes moldy because it was not stored properly. In fact, corn may already carry mold while growing in the field; around one quarter of the corn has already been contaminated by mold by the time of harvest. New corn has high moisture content and more kernels are damaged during threshing, so when piled together it is more prone to heating and mold growth.
There is a basic guideline for selecting corn: moldy kernels should be less than 1%, and impurities should be less than 1%. In practice, look for these signs: if the corn husk separates very easily and there is a large blackish-gray area inside the germ, the corn is moldy; good corn tastes sweeter the more you chew it, while moldy corn tastes bitter; put a handful in water—many floating kernels are usually underfilled or moldy; if it feels prickly in your hand, is hard to dent with a fingernail, and makes your teeth vibrate when bitten, its moisture level is about right.
Severely moldy corn must never be fed. Don’t think “mixing in a little is fine”—toxins accumulate.
The same drying ground: normal corn in the back, moldy corn with green-black mold spots in the foreground
Three or four main toxins, each affecting different parts
The most troublesome thing about mycotoxins is that corn can look perfectly fine while toxin levels may still exceed limits; you can’t sort them all out by sight. Four common types, each affecting a different area:
① Aflatoxin B1 — damages the liver and suppresses immunity
Pigs’ resistance declines, making them prone to secondary diseases. The most typical sign is that vaccines are administered on schedule, yet antibody levels remain persistently low. National standard: no more than 20μg/kg in complete pig feed, and no more than 10μg/kg in piglet concentrate feed.
② Vomitoxin (DON) — specifically causes “not eating”
Among all livestock and poultry, pigs are the most sensitive to it. Signs include feed refusal, reduced feed intake, and vomiting. Feed intake fails to increase, making it a major hidden cause of slow growth in fattening pigs. Limit for complete pig feed: 1mg/kg.
③ Zearalenone (ZEN) — targets reproduction
Replacement gilts develop swollen, reddened vulvas and false heat, and repeatedly fail to conceive; pregnant sows may experience early embryonic death, miscarriage, stillborn piglets, and mummified fetuses. This is the most damaging issue for farrow-to-finish pig farms.
④ Fumonisin (fumonisin toxin) — damages the lungs
Piglets may develop pulmonary edema, and it is also associated with “splay leg.” The limit for complete pig feed is 5 mg/kg.
Corresponding effects on the herd:
· Sows: abortion, stillbirths, failure to come into estrus after farrowing, and refusal to eat during lactation;
· Newborn piglets: swollen vulvas and neurological symptoms such as tilting the head to one side and pressing against walls; death within a few days;
· Fattening pigs: normal body temperature but reduced appetite; red spots on the skin around the mouth, ears, inner sides of the limbs, and abdomen; later, diarrhea or constipation, with mucus and blood in the feces;
· Boars: testicular atrophy and decreased semen quality.
Whenever a pig farm experiences “reproductive problems with no identifiable cause + vaccine antibody levels that fail to rise + sporadic skin redness,” have the feed tested for toxins instead of assuming it is a disease.
Four. How to use new corn safely
Step one, reduce the moisture content. Dry it in the sun or with a dryer as soon as possible to below 14%; this is the prerequisite for all subsequent steps.
Step two: Age it if you can; if you need to use it urgently, transition gradually. The safest approach is to store it for 5–6 weeks before use. If you really can't wait, mix old corn with new corn, gradually increasing the proportion of new corn and allowing about half a month for the pigs' digestive tracts to adapt.
Step three: Sieve and winnow. Remove broken kernels, insect-damaged kernels, and impurities—the toxins are concentrated precisely in these broken and insect-damaged kernels. It doesn't take much effort, and the effect is direct.
Step four: Mix feed as needed and feed it promptly. Feed made with new corn has a high moisture content and is not suitable for long-term storage; after corn is ground, its fat can easily turn rancid. It's best to mix and feed it fresh, rather than preparing a large batch and storing it for several days.
Step five: Control temperature and humidity during storage. Keep the warehouse well-ventilated, dry, and protected from moisture and pests. Strictly follow "first in, first out"; don't let old feed sit at the bottom of the warehouse for a year.
Step six: Use mycotoxin binders correctly. There is a common misconception here: mold inhibitors and mycotoxin binders are two different things. Mold inhibitors suppress mold growth and do not adsorb toxins that have already been produced; to address existing toxins, an adsorbent is needed. Commonly used montmorillonite and bentonite mainly adsorb aflatoxins and have very weak adsorption capacity for deoxynivalenol, so choosing a broad-spectrum product is more reliable. Add it according to the instructions. It is recommended to include it in sow and boar feed year-round.
What should you do in case of poisoning? Immediately stop using the suspected feed, switch to clean feed, and add an adsorbent. At the same time, support and protect liver function and supplement with vitamins C and E to aid recovery. Have a licensed veterinarian determine the specific medication plan. Breeding pigs with severe reproductive disorders or neurological symptoms should be culled when necessary.
Self-mixing pig farms: Sifting, mixing feed as needed, and managing inventory are more effective than treating mold contamination after the fact.
Five. Use different approaches for different pig groups.
Piglets are the most sensitive, so avoid using new corn if possible. During the creep feed and weaned piglet feed stages, the gut is still underdeveloped. Diarrhea caused by resistant starch is most pronounced, and piglets are also most sensitive to toxins. At this stage, good-quality old corn is recommended. If new corn must be used, be sure to age it sufficiently, screen it strictly, and extend the transition period.
For pregnant sows, pay close attention to zearalenone. Embryos are most vulnerable in early pregnancy, and even low levels of ZEN may cause early embryonic death and miscarriage. Corn used in gestation feed should come from a reliable source, with clearly identified batches. It is better to spend a little more on clean feed than to gamble with an entire litter.
For boars, monitor semen quality. The effects of toxins on the testes and semen quality often show up before any visible signs. By the time you notice that sows are not getting pregnant or are returning to estrus more often, the losses have already occurred. It is recommended to add a mycotoxin binder to boar feed year-round and to use aged corn.
Fattening pigs are relatively tolerant, but the costs still need to be calculated. New-crop corn can be introduced during the fattening phase, but the drop in feed intake caused by deoxynivalenol can directly delay market readiness, so the applicable limits must still be observed. The money saved on feed is often not enough to make up for the loss in growth rate.
Six. The four most common mistakes
First: “It looks fine, so it must be toxin-free”—toxins are invisible, so testing is necessary.
Second, “New corn is cheap, so replace it all with new corn”—this is the most dangerous approach.
Third, “It’s safe once a mold inhibitor has been added”—preventing mold is not the same as removing toxins.
Fourth: “There isn’t much mold, so mix it in and feed it” — toxins accumulate, and the more you mix in, the worse it gets.
The feed used in autumn and winter directly determines a sow’s reproductive performance for the year and the finishing costs for pigs. New corn is a good thing, provided its moisture and mold are kept under control.