Cattle Stall Dividers If you’ve ever spent time around young dairy or beef calves, you know how much they rely on their pens—those small, contained spaces where they sleep, eat, and learn to thrive. As a calf pen supplier who’s worked with hundreds of ranchers and small-scale dairy owners over the last 12 years, I’ve seen firsthand how one small, avoidable problem can derail even the most careful calf-raising routines: mold. Not only does mold make pens smell musty and look unkempt, but it’s also a hidden danger— it irritates calves’ delicate respiratory systems, leads to reduced feed intake, and can even trigger long-term health issues that stunt growth. I’ve lost count of how many times a farmer has called me in a panic, saying their 4-week-old calves came down with a cough “out of nowhere,” and when we checked their pens together, we found patches of dark, fuzzy mold tucked between the pen flooring and the wall, or lingering in the gaps of their old, poorly designed pens. The good news? Preventing mold in calf pens isn’t just about scrubbing harder—it’s about designing the right space, maintaining consistent routines, and using materials that fight mold before it even has a chance to grow. Over the years, I’ve tested dozens of ideas with my own small herd on our family farm, and collaborated with vets and agricultural specialists to refine these steps. Today, I’m sharing what works, what doesn’t, and how my team’s pen designs are built to cut mold risk by more than 60% compared to standard wood or metal pens, based on feedback from 200+ ranchers who’ve switched to our systems. Let’s start with the basics: mold needs three things to grow—moisture, oxygen, and an organic food source (think hay, manure, or even old wood fibers). Remove any one of these, and mold can’t take hold. Most of the mistakes I see come from overlooking how easy it is for pens to trap moisture, especially for newborn calves that urinate frequently and trample hay into every crevice. The first, and most critical step to mold prevention is choosing the right flooring for your calf pens. For decades, ranchers used solid wood planks or concrete, but both have major flaws when it comes to moisture. Wood holds onto dampness even after it dries, creating a perfect breeding ground for mold spores that float in the air. Concrete, on the other hand, is solid—manure and urine get trapped between the calf’s hooves and the concrete surface, seep into tiny cracks over time, and stay moist for days. A few years ago, I designed our core calf pen flooring by combining food-grade, non-porous high-density polyethylene (HDPE) slats with a subtle slope (1% grade, enough to let liquids drain away without making the pen slippery). The slats have evenly spaced, narrow gaps (1.5 inches wide) that let urine and feed waste fall through, instead of sitting on the surface. I tested this against traditional flooring on our own farm: a side-by-side of two identical pens, one with our slatted flooring and one with concrete, left for 7 days without cleaning. The concrete pen had 8 distinct mold patches by day 5, while the HDPE pen had zero. The reason? HDPE doesn’t absorb moisture, and the gaps prevent waste from pooling. But flooring alone isn’t enough—you also need to adjust how you place and anchor the pen to the ground. I’ve seen too many farmers set their pens directly on bare dirt or grass, which soaks up moisture from rain or morning dew and wicks it up into the pen’s base. That’s why all our calf pen systems include a 4-inch high, removable plastic base that sits between the flooring and the ground, creating an air gap that stops dampness from seeping upward. It also makes cleaning the base quick: just hose it down every few days, and you don’t have to dig or scrape dirt. Next, let’s talk about air flow—mold hates moving air, but many calf pens are set up in tight, sheltered corners that trap humidity. Newborn calves don’t like drafts, so you have to balance ventilation with temperature control, especially in cold climates. A mistake I used to make was placing pen walls too high (18 inches, back when I first started building small pens) which blocked air circulation without keeping calves warm. Now, our standard pen walls are 12 inches tall, made from the same non-porous HDPE as the flooring, with a 2-inch gap at the top and bottom that lets small amounts of air pass through, but not enough to create a cold draft on calves. For outdoor pens, we also recommend adding a temporary wind break made of lightweight mesh, which keeps harsh winds out but still lets air flow freely. For indoor barn pens, we work with farmers to position pens at least 3 feet apart from each other, so there’s space for air to circulate between them, instead of lining them up tight against the barn wall. Humidity is another big factor—most ranchers don’t track it, but indoor barn humidity levels above 55% are a mold magnet. I suggest placing a $10 hygrometer (a device that measures humidity) near the calf feeding area, and if levels go above that, cracking a barn window or turning on a small, low-powered fan (no more than 50 CFM) for 2 hours a day. I tested this on a dairy barn in central Wisconsin last winter, where humidity regularly hit 62% without ventilation. After adding small fans between pen rows, mold levels dropped by 70% over 2 weeks, according to the farm’s vet. Now, let’s get to the daily and weekly routines that keep mold at bay, even if your pen is well-designed. This is where many farmers cut corners, especially during busy calving season when they’re juggling dozens of newborn calves at once. First, spot cleaning should happen every single day. I tell every farmer I work with to check the pen for wet spots, trampled hay, or clumps of manure twice a day—once in the morning before feeding, and once in the evening before bed. If you leave wet hay or manure in the pen for more than 12 hours, mold spores that landed there will start growing. Our pen design makes this easy: the slatted flooring lets waste fall through, so you only need to pick up any hay that’s been pushed to the edges of the pen, not scrape the entire surface. For deep cleaning, I recommend a full clean every 7 to 10 days, depending on how many calves are in the pen. When you do a deep clean, skip harsh chemical cleaners—they can leave residues that irritate calves, and some even kill the “good” bacteria that help prevent mold. Instead, use warm water and a small amount of white vinegar (1 cup per gallon of water) to scrub the pen flooring and walls. Vinegar is mild, non-toxic, and kills mold spores on contact without leaving fumes. After cleaning, let the pen air dry completely before putting new calves in. I’ve seen farmers put calves back in pens 30 minutes after cleaning, and that’s a surefire way to bring mold back—any leftover moisture trapped under the slats or in wall gaps will start growing within 48 hours. If you’re in a rainy or humid climate, set the cleaned pen in the sun for 2 hours before restocking—UV light also kills mold spores, which is a free and easy step. One mistake many calf owners make is over-bedding. Straw or wood shavings are great for keeping calves warm, but if you layer it more than 2 inches thick, calves will trample it into the flooring gaps, and moisture gets trapped underneath, creating mold food. I recommend a layer of 1 to 1.5 inches of bedding, topped up with a small amount every 2 days, rather than adding a deep layer all at once. This also saves you money on bedding, which is a win for your budget. What about pen placement? If you’re raising calves outdoors, don’t line pens up against a north-facing wall or under a tree that drops leaves and holds dew. Those spots stay damp longer than open, south-facing areas that get sunlight for most of the day. I had a client in Oregon last year who moved his 10 outdoor pens from a shaded, north-facing corner to a sunlit stretch of his pasture. Within a month, he reported no new mold patches, and his calves had fewer respiratory issues. If you have to keep pens in a shaded area, invest in small solar-powered fans for each pen—they run on no extra electricity, and keep air moving 24/7. Now, let’s talk about common myths that I hear all the time. Some farmers tell me, “Wood pens are better because they’re warmer, so my calves don’t get sick.” No—while wood might feel warmer to the touch, it traps moisture, and mold growth from wet wood will make calves sicker than a slightly cooler, well-ventilated pen. Another myth is that metal pens are mold-resistant. While metal doesn’t absorb moisture, it rusts over time, creating small pits where manure and moisture get trapped, leading to mold just like concrete. Our HDPE pens don’t rust, don’t absorb moisture, and don’t have those tiny pits, so they hold up better long-term. I also hear, “Mold is just a small problem, I can wipe it away.” But by the time you see a fuzzy patch of mold, there are thousands of microscopic spores already floating in the pen’s air, which calves breathe in. That’s why the vet I work with says reducing mold risk in pens cuts calf pneumonia cases by 40%—a huge number for a farmer, since treating pneumonia can cost hundreds of dollars per calf. Over the last 12 years, I’ve built and installed thousands of calf pens, and I’ve seen how small adjustments make a big difference. Last spring, a new dairy farmer from Iowa reached out to me, saying his 3-week-old calves were being hospitalized for respiratory issues every week, and his vet couldn’t figure out why. When we visited his farm, we found he was using old wooden pens, leaving wet hay in the pens for 2 days at a time, and had no ventilation in his indoor pen barn. We replaced his pens with our HDPE slatted systems, showed him how to spot clean daily, and set up small fans for ventilation. By the next month, he called me saying no calves had been hospitalized, and he’d saved $1,200 in vet bills. That’s the kind of result that makes all the testing and tweaks worth it. If you’re struggling with mold in your calf pens, or you’re looking to upgrade your pen system to reduce mold risk, I’d love to walk through your setup with you. Whether you’re a small-scale farmer with 5 calves or a large dairy with 100, we can design a pen system that fits your space, budget, and needs—all built with mold prevention at the core. You don’t have to let mold slow down your calf-raising operation, and you don’t have to spend hours scrubbing or replacing pens every year. With the right design, consistent routines, and a small focus on moisture and air flow, you can keep your calves healthy, your pens clean, and your operation running smoothly. Don’t wait until mold leads to sick calves or lost time—reach out to me today to discuss how we can adjust your pens for better mold resistance.
References Calf Pens
- National Research Council. (2001). Nutrient Requirements of Dairy Cattle (7th rev. ed.). National Academies Press.
- Radostits, O. M., Gay, C. C., Hinchcliff, K. W., & Constable, P. D. (2007). Veterinary Medicine: A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses (10th ed.). Elsevier Health Sciences.
- Agriculture and Horticulture Development Board (AHDB). (2020). Calf Housing and Management Guidelines for Disease Prevention. AH Dairy.
- Miller, W. G., & Kasari, T. R. (2018). “Environmental Factors Affecting Respiratory Health in Pre-Weaned Calves.” Journal of Dairy Science, 101(12), 11245-11256.
- American Society of Agricultural and Biological Engineers (ASABE). (2021). Standard for Calf Housing Design and Performance. ASABE.
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