Determining Supplementation for Grazing Livestock

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Livestock nutrition is based on several metrics. When we talk about grazing livestock we first must think of the two Qs: Quantity and Quality of our forages. Quantity refers to the amount of forage available to the animal and quality is the ability of the forage to support a desired level of performance. Forage based systems are often the most economical feed option; however, we need to know the quantity and quality of forages first. The quantity and quality of the forages will aid in determining if the available forages are meeting the nutrient requirements of our animals. Other helpful things to know are the physiological status (bred vs. open), level of production (ewe nursing single lamb vs. twins), and body condition score (fat vs. thin) of our livestock. The quality of the nutrition offered will have an impact on animal performance. But how do we know if our forage is meeting the nutrient requirements of livestock to support their stage or level of production? There are several things that should be evaluated when determining if supplementation is necessary, like forage quantity and quality. Below are few metrics for evaluating if supplementation is needed and should be incorporated into your feeding program.

Forage Appearance

Let’s keep it simple. Below is a crude method for making a quick assessment; however, a forage analysis is highly encouraged and recommended in order to truly know the nutrient composition of the forages.

Do your livestock have all they can eat in their pasture?


  • Yes – Forage quantity is adequate.
  • No – Forage quantity is inadequate. There is likely an energy deficiency because of the low forage availability.

Quality (color)

  • Brown – Likely forage is protein deficient. For ruminants (cattle, sheep, and goats), protein deficiency has the ability to limit forage intake and digestion.
  • Green – Likely forage is adequate in protein, but remember to check quantity! Do they have enough to eat? See quantity.
  • Visual appraisal has its place, but remember submitting a forage sample for analysis is best.

Body Condition Score (BCS)

  • Are your animals in adequate BCS?
    • Over-conditioned? If forage quantity is an issue, considering bringing in a protein supplement for ruminants to help with rumen efficiency.
    • Under-conditioned? Energy and protein supplementation may be necessary depending on the forage quantity and quality.

Stage and Level of Production

  • The physiology status of livestock is very important to know. For examples, dry, non-pregnant cows can get by on fewer inputs (e.g. groceries!), but a lactating cow in early gestation will have higher nutrient requirements than her dry, non-pregnant counterpart.
  • A mature wether that is a pasture companion or a pet for the grandchildren will not have high nutrient requirements like a young, growing ram that will be expected to breed his first year of life.

Forage Analyses

  • Visual appraisals of forages have distinct limitations, but are still important; however, performing forage analyses to assess the nutrient composition of the forages is recommended. Knowing the amount of energy, protein, and digestibility of the forages will help determine the amount and level of supplementation to provide to livestock.

Level of Performance

  • This one can be a bit more abstract. Like milk production on a beef cow – no, we do not expect you to milk your beef cows; however, you can gauge milk production based on calf performance. Is the calf thrifty, is she hitting target weight gains?
  • Poor performance indicators may be things like low birth weights, decreased reproductive performance, poor fleece quality, decreased milk production. Poor performance indicators like these should sound the alarm to access and evaluate your current feeding program.

Having the right balance of nutrients will be key in helping your livestock meet their performance potential. The metrics above are intended to be a quick starter guide to helping you assess the need for supplementation and not comprehensive for establishing a supplementation program. For more information about supplementation programs see your County Livestock Agent to get started.