Determining nutritive value of grazed forage is difficult and producers generally make assumptions about when forage nutritive value is low enough to warrant supplementation. The assumptions are not always correct because forage nutritive value is dynamic depending upon climate conditions and grazing management. Thus, cows are sometimes over or under supplemented.
Fecal consistency can provide clues as to the nutritive value of forages. Cows grazing lush green forage in the spring generally have very loose feces indicating low concentrations of fiber and high concentrations of protein. In contrast, cows grazing dormant standing forage in the winter will have very firm and dry feces indicating high concentrations of fiber and low concentrations of protein. These two extremes are easy to identify that the cows with loose feces do not need supplementation and the cows with firm dry feces need protein supplementation, and maybe energy supplementation, which is more difficult to discern from visual observation of feces.
A more detailed evaluation of feces can provide more information leading to better supplementation strategies and timing. Near infrared spectroscopy (NIRS) is a tool to quick determine the chemical composition of a feedstuff or a fecal sample. Chemical analysis of fecal samples for protein and digestibility using NIRS coupled with a simple nutrition model can improve supplementation strategies of grazing cattle. This can be done with the help of the Grazingland Animal Nutrition Laboratory.
A recent study evaluated the use of the NIRS and a nutrition model in a cow herd in west Texas. The study compared two NIRS calibration analyses: a U.S.-scale calibration and a west Texas calibration. The U.S.-scale calibration poorly predicted the forage protein, but the west Texas calibration prediction of protein was much better indicating that regional calibration may be necessary for accurate prediction. The west Texas calibration coupled with the nutrition model was moderately accurate and precise in predicting body condition score of the cows. Possibly more importantly, the west Texas calibration coupled with the nutrition model was able to estimate changes in body condition score over time.
Forage nutritive value would change before body condition score. Being able to monitor changes in forage nutritive value through fecal analysis coupled with the nutrition model prediction of body condition changes would allow implementation of supplement strategies before changes in body condition occur. In conclusion, fecal analysis can be useful in determining supplementation strategies, but care should be taken that the NIRS calibration matches the local conditions.
