Evaluating Diet Adequacy in Grazing Situations

March, 2013
Randy Gornto, Highlands County Livestock Agent, UF/IFAS

There are two problems that limit the ability to adequately evaluate cattle's nutritional status:

  1. We don’t know how much they are eating. We can predict intake to some extent but they are still guesses.
  2. We don’t know the nutrient content of the diet because cows selectively graze the forage available.

Our inability to answer these questions with a high level of accuracy makes the use of body condition scoring essential. We can only make educated estimates about the amount and composition of the diet, provide supplemental nutrients when they appear needed, and use body condition changes over time to monitor the adequacy of the diet.

It would seem logical that we could take samples of the forage available to balance the ration but the problem is that cows selectively graze, which means that the diet they consume will be different than the clipped sample. According to Dr. Arthington he had grad students try and select along with the cow and the cow always selected better than the student. What we do know from those trials is that on average, the differences was about 2% in protein provided that there is adequate forage available to allow selectivity. Remember clipped samples are what the cattle did not eat, at least not yet.

Below are factors to consider in assessing the diet of cattle in grazing situations:

  1. Adequate forage available.
  2. Positive allowances should be made for selective grazing.
  3. Nutrient content of dormant forages decline over time.
  4. Nutrient composition of forages varies from year to year.
  5. Monitoring cow condition is essential as an indicator of the adequacy of the diet.

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