Faecal near infrared reflectance spectroscopy to predict diet quality for sheep

Abstract

Faecal near infrared reflectance spectroscopy (NIRS) is a non-invasive method to determine diet quality in herbivores, but has not been reported for sheep ( Ovis aries) in US. A diet reference chemistry:faecal near infrared spectra calibration ( n = 78) was developed to determine if faecal NIRS can predict diet quality of forage-fed sheep. In 2002 ( n = 15) and 2003 ( n = 20) mature ewes (55 ± 2.4 kg) were fed individual diets for 7 days. Diets ranged from 4.3 to 23.5% crude protein (CP) and 52.4 to 75.8% digestible organic matter (DOM) and were composed of various grass, forb and browse components. Daily intake was recorded. Faecal samples were collected on days 6 and 7. CP was determined by micro-Kjeldahl and DOM by an in vivo corrected in sacco technique. Partial least squares (PLS) and stepwise regression (SWR) techniques were used to develop predictive equations. Calibration results for percent dietary CP were: SWR, R 2 = 0.93, SE calibration (SEC) = 1.27 and PLS, R 2 = 0.95, SEC = 1.08. Calibration results for DOM were: SWR, R 2 = 0.78, SEC = 1.58 and PLS, R 2 = 0.80, SEC = 1.51. Equation validation was accomplished by cross validation, predicting an independent validation set, and by predicting day 7 samples with a day 6 derived equation within this study. Validation results indicate acceptable predictive ability. To determine the effect of individual animal variation on faecal NIRS predictions, five ewes were fed different forages in two, 7-day trials. Predicted percent CP and DOM from both trials indicate minimal effect on NIR predicted diet quality due to individual animal variation. Diet quality of forage-fed sheep can be accomplished by faecal NIRS.