Stanton PhD Thesis final_docx - Atrium - University of Guelph

(cases) and two calves closest in age to the affected calves, but with no history of ear droop, were
sampled. Case and control calves were not re-sampled.
Study personnel wearing sterile disposable gloves used swabs moistened with
mycoplasma enrichment medium to swab the nares of selected calves. Swabs were placed in
enrichment medium and shipped to the Mastitis Research Laboratory at Washington State
University in Pullman, Washington. Specimens were incubated at 37 o C in 10% CO2 for 4 days.
On the fourth day, 100 µL of enrichment medium was streaked on a Mycoplasma agar plate
(Hogan et al., 1999). Plates were incubated at 37 o C in 10% CO2 for 7 to14 days, then examined
with a 15X dissecting microscope for colonies with the distinctive “fried-egg” appearance
(Hogan et al., 1999). Results were considered positive if any Mycoplasma colonies were seen
and negative in the absence of Mycoplasma growth. Speciation was done using PCR analysis,
and fingerprinting for type was performed using pulsed- field electrophoresis patterns of the
positive isolates as described by Biddle et al, ((Biddle et al., 2005).
5.3.5 Statistical Analysis
All analyses were performed using SAS® statistical software (SAS Institute Inc., Cary,
NC) v 9.1, with statistical significance based on Type III test for fixed effects having a P-value ≤
0.05. All models were built using backward step-wise elimination. Normality was assessed for
all linear models.
The associations between disease events and ADG and height at study completion were
analyzed using a linear mixed model (PROC MIXED) with random effects for source farm,
location of barn or hutch system, and cohort group nested within housing location. A cohort
group was defined as animals in the same housing system at the same time. Disease outcomes
110