The Importance of Fiber in Ruminant Diets

Fiber in ruminant diets: From lab reports to rumen health When we talk about protein, starch, or fat in ruminant diets, fiber sometimes gets labeled as “filler.” 👉 But the truth is: fiber is the steering wheel of the rumen. It controls how much animals can eat, how efficiently they use feed, and whether the rumen stays healthy. 🔎 What is fiber made of? (Van Soest system) NDF (Neutral Detergent Fiber): hemicellulose + cellulose + lignin Main predictor of dry matter intake (DMI). More NDF = less intake. ADF (Acid Detergent Fiber): cellulose + lignin Related to energy supply. Higher ADF = lower digestibility (TDN/NE). ADL (Acid Detergent Lignin): lignin itself Indigestible “wood.” The more ADL, the less cellulose and hemicellulose microbes can use. 📚 How nutrition models use fiber CNCPS (Cornell Net Carbohydrate & Protein System): Divides NDF into pdNDF (potentially digestible) and uNDF (undigestible). uNDF240 (residue after 240 hours) predicts rumen fill and passage rate. Digestibility depends on kd (%/h), usually 2–6%/h. NRC (Dairy & Beef): Uses NDF, lignin, and peNDF to predict DMI, energy supply, and milk fat. Forages with less lignin and faster pdNDF improve intake and energy use. CVB (Netherlands): Reports NDFom/ADFom to calculate energy (VEM/VEVI) and fill values. More lignin/uNDF = less energy, reduced intake. 👉 In simple terms: Too much lignin/uNDF → animals feel full too quickly, intake drops. Too little effective fiber → acidosis, milk fat depression, loose manure. 🌾 Physically effective fiber (peNDF) Not all fiber stimulates chewing! peNDF = NDF × pef (particle effectiveness factor). pef = % of particles >1.18 mm (Penn State shaker). Adequate peNDF = stable rumen pH, good cud chewing, healthy milk fat. Without enough peNDF, even if NDF is “on paper,” the rumen is at risk. 📌 Practical target ranges (per NRC, CNCPS, CVB, INRA) Dairy cows (high yield): NDF: 28–34% DM Forage NDF: ≥19–21% DM peNDF: ~19–21% DM uNDF240: 9–13% DM Beef finishing cattle: NDF: 20–28% DM peNDF: 12–15% DM Dairy goats: NDF: 28–35% DM peNDF: 17–20% DM Note: goats sort feed → monitor particle size. Sheep: Finishing lambs: 25–30% NDF Ewes (gestation/lactation): 30–36% NDF Balance uNDF: too high = poor intake; too low = digestive upset. ✅ On-farm checklist Always ask for NDFom, ADFom, ADL, and uNDF240 if possible. Don’t let grain overload without enough effective fiber. Corn silage TLC 1.5–2 cm, include some long hay. Observe animals: Cud chewing: >55% of lying cows chewing = good Manure: firm, not watery, little undigested grain Milk fat: butterfat-to-protein ratio >1.2 in dairy 🚀 Take-home message Fiber is not just bulk — it decides intake, efficiency, and animal health. NDF, ADF, ADL, and peNDF connect lab reports to real-life performance on the farm. By combining forage analysis with nutrition models (CNCPS, NRC, CVB), you can fine-tune diets that support better production, healthier animals, and more sustainable farming. By: Bogdan Cekić