Why Hay Testing Matters 

Hay is the backbone of most winter feeding programs, but its nutritional value can vary widely depending on forage species, maturity at harvest, soil fertility, and storage conditions. Without testing, it’s impossible to know exactly what nutrition is being provided to the herd, which can result in underperformance, wasted feed, or unnecessary supplementation.

Testing hay provides the information needed to make informed, cost-effective feeding decisions that support herd health and productivity.

Decoding Hay Test Results: Which Numbers Matter Most?

Many producers receive a hay analysis report and wonder which values are most important. Here’s a breakdown of the key numbers and what they mean:

Relative Feed Value (RFV): Know Its Limits

  • RFV is calculated from fiber content and was originally designed to rank alfalfa for dairy cows.

  • RFV often underestimates the value of grass hay because grass fiber can be more digestible than alfalfa fiber.

  • For beef cattle, RFV is less useful and can be misleading.

  • Don’t rely on RFV alone to assess grass hay for beef cattle.

Crude Protein (CP): The Growth and Reproduction Driver

  • Crude protein measures the hay’s ability to support growth, reproduction, and milk production.

  • Protein is essential for muscle development, fetal growth, and milk yield. If protein is lacking, animal performance and health will suffer.

  • For beef cows, the CP value is usually adequate to determine if the feed will meet requirements.

Total Digestible Nutrients (TDN): The Energy Gauge

  • TDN measures the energy content of the hay, combining digestible fiber, protein, fat, and carbohydrates.

  • Energy is crucial for maintaining body condition, supporting reproduction, and driving animal performance—especially for lactating cows or growing calves.

  • Hay with less than 52% TDN is considered low quality; 52–58% is average; above 58% is high quality. Lactating cows need at least 58–61% TDN, while dry pregnant cows need 50–54%, depending on stage of pregnancy.

Practical Advice: How to Use Hay Test Results

  • Test every lot. Hay quality can vary even within the same field or cutting. Sample and test each lot separately to get accurate results.

  • Sample properly. Use a hay probe to collect core samples from multiple bales per lot, sampling from different locations in each bale for a representative mix.

  • Match hay to animal needs. Feed the highest quality hay to animals with the greatest nutritional demands—such as lactating cows, growing calves, or late-gestation cows. Lower quality hay can be reserved for mature bulls or open cows with lower requirements.

  • Monitor for nitrates. Especially in drought years or with certain forages, test for nitrate levels to prevent toxicity, which can cause illness or sudden death in cattle.

The Bottom Line

For beef cattle producers, the most important numbers on a hay test are crude protein and TDN. RFV is less relevant for grass hay and can be misleading. Always test hay and use the protein and energy values to guide feeding and supplementation decisions. This ensures the herd gets what it needs for optimal health and performance, while helping manage feed costs effectively.

Testing hay is a small investment that pays big dividends in herd productivity, feed efficiency, and peace of mind. Don’t guess—test!