What is NIRS?
The NIRS process involves exposing a dried, ground fecal sample to light energy. The intensity of
reflectance is measured across several hundred wavelengths in the near infrared band. Reflectance
is influenced by number and type of chemical bonds in the feces. Primary wavelengths in prediction
equations appear to be associated with the fiber, alkane and microbial fractions of the feces.
Predicting Diet Quality
Known diet samples were matched with feces of intact cows grazing a wide variety of forages.
These diet:fecal pairs were used to develop a reference data set to build prediction or calibration
equations. Fecal equation diet quality predictions were then validated against herds with known diet
qualities. Equations developed to date appear to be highly reliable across a broad spectrum of forage
types. Currently, the lab can predict dietary crude protein (CP%) and digestible organic matter
(DOM%) as well as fecal nitrogen (FN%) and fecal phosphorus (FP%). Dietary content of dicots can
be estimated for regions of contrasting C3 dicot species (forbs and browse) and C4 warm-season grasses.
Linking NIRS with Computers
Diet quality information can be linked with the decision support system Nutritional Balance Analyzer
(NUTBAL-PRO). This software planning tool lets the user enter the kind, class, and breed of animal
to be monitored, characterize body condition and environmental conditions, establish weight performance
targets, and then enter the NIRS diet quality results. The program produces a nutritional balance report
for protein and net energy. If a deficiency exists, the user can use NUTBAL-PRO or other analytical tools
to determine the amount of least-cost feedstuff needed to correct the problem.
Prediction of Dietary Protein Fractions Using NIRS Technology
A major limitation to application of a more advanced nutritional management model is the inability
to predict the level of degradation of crude protein in the rumen and lower gut of free-ranging animals.
NIRS technology has been successfully used to predict dietary crude protein (CP) and digestible
organic matter (DOM) of free-ranging animals (Lyons and Stuth 1993) and Spanish goats (Leite and Stuth 1995),
via fecal profiling. When combined with the Nutritional Balance Analyzer (NUTBAL-PRO) decision support
system, NIRS fecal profiling provides the necessary monitoring tool to allow assessment of CP and
net energy of maintenance/gain (Nem/NEg) (Stuth and Lyons 1995). In order for this nutritional management
tool to account for site of protein degradation, appropriate monitoring technology must be developed
to support the decision process. This research explored the potential of NIRS technology to predict
degraded intake protein (DIP), digestible undegraded protein (DUP) and indigestible intake protein (IIP).
This research project was conducted in collaboration with experiment stations at various sites in the mid-South Texas, Central Texas, Central Oklahoma, and Central Missouri. Extrusa was subjected to laboratory techniques at the Grazingland Animal Nutrition (GAN) Laboratory on the campus of Texas A&M University. Laboratory values were regressed against matched fecal spectra using a Perstorp Scientific 6500 machine equipped with ISI software. In order to derive equation feasibility, hierarchical guidelines were followed, based on recent literature, that addressed both statistical parameters as well as biological reality. This research program served as an indication to the feasibility of utilizing NIRS technology to predict differential sites of protein degradation in the gastro-intestinal (GI) tract of free-ranging cattle. Equations that estimate protein availability in the entire GI tract are available to aid in nutritional decision making processes. This technology, when coupled with NUTBAL=PRO, will yield information that gives insight on requirements being met by forage at specific sites in the GI tract of free-ranging cattle. Alternatively, supplementation could be evolved around this technology to yield a more efficient nutritional program based on meeting requirements at specific protein degradation sites.
Citations:
Lyons, R.K. and J.W. Stuth. 1992. Fecal NIRS equations for predicting diet quality of free-ranging cattle. J. Range Manage. 45:238-244.
Leite, E.R., and J.W. Stuth. 1995. Fecal NIRS equations to assess diet quality of free-ranging goats. Small Ruminant Research. 15:223-230.
Stuth J.W., and R.K. Lyons. 1995. NIRS-NUTBAL Nutritional management system for cattle. In: Ellen R. Jordan (ed.)
Proceedings of Mid-South Ruminant Nutrition Conference.