How to Starve Animals with a Full Stomach

“What do you mean my cow/horse/sheep/goat/ llama/alpaca/elephant died of starvation? She had all the hay she could eat!”

Sadly, these words are sometimes uttered by livestock owners experiencing a painful lesson about hay quality. Some hay is of such low quality (Photo 1) it can’t support maintenance nutritional requirements, let alone growth, lactation, pregnancy, or work. This article will focus on grass hay, but the basic principles discussed also pertain to legume and mixed grass/legume hay.

Quality Affected by Harvest Time

Two crucial components of hay quality are protein content and fiber content. As depicted in Table 1, protein content decreases and fiber content increases with increasing grass maturity. Grass harvesting is a compromise between quality and quantity because the two are inversely related. Early harvested grass will be high quality (higher protein content, lower fiber content, and higher fiber digestibility) but the hay yield will be low. Late harvested grass will be lower quality (lower protein content, higher fiber content, and lower fiber digestibility) but more hay tonnage will be harvested.

Grass harvest time is affected by weather and soil conditions: it must be delayed until soils are dry enough so harvesting equipment does not get stuck and mowing, raking, and baling activities will not damage soils excessively. Reed canary grass (RCG) is a prolific grass that does well in wet areas. It can be difficult to make good quality RCG hay because by the time haying equipment can get onto RCG areas, the plants can be very mature. This will result in a great amount of harvested grass, but the quality will be even less than that of the “dough phase” shown in Table 1.

Table 1. Typical Chemical Composition of Grasses. From “Using a Hay Test for Feeding Livestock” presentation by Shelby J. Filley, Oregon State University Extension Service Regional Livestock and Forage Specialist. CP = crude protein. ADF = Acid Detergent Fiber. NDF = Neutral Detergent Fiber.
Maturity CP ADF NDF
Veg-Boot > 18 < 33 < 55
Boot-early Head 13-18 34-38 55-60
Head-Milk 8-12 39-41 61-65
Dough < 8 > 41 > 65

Fiber Content and Hay Quality

Neutral detergent fiber (NDF) includes all types of plant cell fiber: cellulose, hemicellulose, and lignin; it estimates hay intake by animals and a low number is desirable. Acid Detergent Fiber (ADF) includes the less digestible parts of plant cell fiber: cellulose and lignin; it estimates fiber digestibility and a low number is desirable. Both types of fiber increase with increasing plant maturity. Photo 2 is a visual metaphor of a plant cell using a cardboard box to represent the outer cell wall (cellulose; digestible), plastic bag to represent the lignin layer (completely indigestible), paper wrapping to represent the inner cell wall (hemicellulose; digestible), and sugar to represent cell contents (sugars, protein, fat, pectin, and starch; extremely digestible).

RCG can easily be 5 to 6 feet tall when the soil in which it is growing is dry enough for heavy equipment. Plants this tall need to produce more structural fiber to stand up; this is lignin, which is completely indigestible. NDF and ADF of mature RCG will be very high, so both feed intake and digestibility will be reduced.

  • Desirable Hay Fiber Levels:
  • NDF: <50%
  • ADF: <35%

Protein Content and Hay Quality

Like fiber digestibility, protein content of grasses decreases with increasing plant maturity. Young plants—even RCG—can have impressive crude protein (CP) levels, sometimes exceeding 20% on a dry basis. For ruminants, the dietary nadir (lowest amount) of crude protein needed for survival is 7%. Below this, there is insufficient protein for rumen microbes to reproduce, so fiber digestion ceases. The ruminant will be hungry and ingest more feed, but the fiber will be indigestible, the rumen will fill and stay full, and the animal can starve to death with a full stomach.

Fresh Forage vs. Hay

Lush spring grass pasture can have high protein content and high fiber digestibility, but will also have very high water content—as much as 90% of grass weight will be water in early spring. As shown in Table 2, if pasture is made available to livestock on an as- fed basis (i.e., grazed), animals will need to consume a great deal of fresh forage to meet their intake potential and nutritional requirements compared to hay, from which most water weight has been removed.

Table 2. Fresh forage vs. hay intake for 1200 lb. mature beef cow at 3% body weight of dry matter ingested.
Forage Type % water % dry matter # forage
Fresh forage 90 10 360
Hay 10 90 40

How to Prevent Full Belly Death

The only way to know the nutritional value of hay is to test it. The Resources shared below describe how to take a forage sample for analysis, where to send it, and how to interpret results. The testing laboratory, Extension educators, veterinarians, and livestock nutrition consultants can also help with interpreting and using the information contained in forage analysis reports.

Photo 3 is an example of a low-quality grass hay report from a forage analysis laboratory; note its very low crude protein content and high ADF, NDF, and lignin levels. Its Relative Feed Value (RFV) is 77.67. As a comparison, mature alfalfa hay has a RFV of 100.

RFV is a way to compare the expected intake and digestibility of various roughages—a higher number is better. Low quality hay such as this example can be included in livestock rations if supplements are provided to meet animals’ energy, protein, vitamin, and mineral requirements. If provided as the sole feed, low-quality hay such as that in Photo 3 cannot maintain any species of livestock at any life stage. Ruminants need a fibrous diet to keep their rumens working well, so savvy producers can use low quality (read: inexpensive) forage as a ration foundation, adding some grain for energy and perhaps lick tubs, barley cakes, dry peas, or a little alfalfa for protein. Body condition scoring, growth rates, milk production, and general health can help assess effectiveness of a nutritional program.


Just as one would not expect a baby to grow well or a triathlete to perform well on a diet of just high-fiber/low-calorie rice cakes, most classes of livestock cannot perform well or remain healthy on low-quality fiber diets. No matter how much low-quality forage they consume, they will not be able to meet their nutritional requirements; they will use body reserves of energy and protein until death ensues. If inexpensive low- quality hay must be incorporated into livestock rations, producers are obligated to supplement the ration with nutrients needed to meet their livestock’s’ nutritional requirements.


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