Mannheimia haemolytica (MH) is a leading cause of bovine respiratory disease (BRD). Diagnosis of BRD traditionally relies on visual assessment, which can be untimely, insensitive, and nonspecific; more rapid and accurate diagnostic tests are needed. Near Infrared Spectroscopy (NIRS) allows fast, noninvasive assessment of biofluids, whereby the chemical profile is described by the intensity and structure of sample reflectance or transmittance spectra in the NIR band (780 to 2500 nm). We hypothesized that NIRS evaluation of breath condensate, nasal secretions, saliva, plasma, and/or serum (biofluids) could profile signatures differentiating cattle before and after MH infection. Biofluids were collected from five 6-month-old Holstein steers over four days prior to and 23 days after intrabronchial challenge with MH. Clinical signs (rectal temperature, heart and respiratory rate, and respiratory score) and complete blood counts (CBC) were assessed pre- and post-challenge. By Day 2 post-challenge calves had signs of acute MH infection with significantly increased (P < 0.05) rectal temperatures, heart rates, and respiratory rates. CBCs revealed significantly increased (P < 0.05) leukocyte and neutrophil counts. Due to severe disease calves were treated with a 5-day course of antimicrobial (AM, ceftiofur hydrochloride). Biofluid samples were grouped into four categories: a) baseline, b) infected, pre-AM, c) infected, post-AM, and d) recovered. Spectral signatures of biofluids (n=3800) collected via ASD FieldSpec®3 portable spectrometer were analyzed with multivariate statistics using Unscrambler®X v. 10.5. Chemometrics were applied to the wavelength range 1300-1600nm using a balanced randomly selected subset of samples (n=150) with an 80/20 Calibration/Validation distribution for Linear Discriminant Analysis (LDA-PCA). Analysis discriminated samples according to category; LDA-PCA showed correct classification between 89.6-100% and 81.7 - 100% for the calibration and validation process, respectively. NIRS with multivariable analysis rapidly discriminated MH infection states in cattle, establishing a basis for further development of NIRS as a BRD diagnostic tool.
Learning Objectives:
Recognize that near infrared spectroscopy can be used to identify signatures in biofluids that indicate infection or inflammation.
Recognize that near infrared spectroscopic signatures in biofluids can distinguish cattle infected with Mannheimia haemolytica from uninfected cattle.
Recognize that new tools like near infrared spectroscopy may improve accurate diagnosis of bovine respiratory disease.
