Pasture and Forage Minute: Deciphering a Hay Test

Courtesy UNL
By Ben Beckman

While typically lower on the lab results, the mineral makeup of forages is no less important than the protein and energy portions we discussed previously. Mineral supplementation can be a big expense in operations, so knowing how to utilize the information in a hay analysis is important.

Mineral demand in animals is highly dependent on your location and feed resources. Forage analysis can help identify possible mineral imbalances in your operation and form the basis for developing a solid mineral program. However, we need to be aware of a few things first.

When dealing with forages, just because a certain amount of mineral is listed in the analysis doesn’t mean it will be 100% available to the animal. Because mineral availability is depended on a number of factors from the feed to animal digestion, only a percent of reported minerals are actually absorbed into the bloodstream. Typically P, K, Mn and Fe are higher in bioavailability; Ca, Zn and Cu in the middle; and Mg absorption is considerably lower. To further complicate things, some minerals are able to be accumulated or stored up in cattle at times when they are in excess and then used as a reserve when diets are deficient.

Using the values provided along with animal intake, an estimate of mineral consumption for each element can be calculated and used when planning a mineral program to ensure animal needs are met without going over and unnecessarily increasing expense. Figuring the right mineral balance for your herd can be a complicated process, so getting help from an expert if needed is always recommended. Those looking for a publication to read might find EC288 — “Minerals and Vitamins for Beef Cows” is a great resource.

Deciphering a Hay Test: RFV and RFQ

By Brad Schick

Two weeks ago, we looked at Total Digestible Nutrients (TDN) or energy and understanding how it is important for the health and nutrition of livestock. TDN is used to calculate forage energy availability to meet animal needs. Now we will look at Relative Feed Value or RFV and Relative Forage Quality or RFQ. 

Both RFV and RFQ take into consideration intake, the energy content of the feed and the use of a standard. 

ADF and NDF have been used to measure fiber and ultimately energy of hay. Labs combine them in to come up with the estimate or relative feed value or RFV. RFV has a downfall because it assumes all fiber digestibility is the same and we all know that’s just not the case. The RFV of grasses is often incorrectly valued because they have a lot of fiber compared to legumes but are more digestible than legumes.

RFQ is a newer, more accurate fiber digestibility lab technique. It also uses ADF and NDF to calculate values, but uses a simulated digestion using rumen fluid to predict forage intake and digestibility. RFQ is more accurate than RFV because it uses actual digestion values. It is a better indicator for grass hay than RFV.

Understanding which measurement of energy to use in an operation is important to calculate livestock needs, which change drastically with different stages of production. Being able to decipher RFQ and RFV will help in the purchasing or marketing grass and alfalfa hay. 

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