Abstract :
In order to use body condition scoring as a cross-farm assessment tool, it is important that
different assessors can consistently grade sheep along the same scale. This paper examined
the intra- and inter-assessor reliability of three trained and experienced assessors
who independently assessed the body condition of 141 Lleyn, Cambridge-cross and Welsh
Mule-crossbred ewes using full- or half-point scoring precision of a six-point ordinal scale.
Assessor reliability was evaluated using percentage (%) agreement, weighted kappa ( w),
and Kendall’s coefficient of concordance (W). Kruskal–Wallis one-way analysis of variance
and graphical representation of the data were also used to examine for assessor bias. The onfarm
studies found that the intra-assessor reliability of an assessor, who provided training in
the scoring method, was higher when half- (96%, w 0.7, W 0.7) rather than full-unit scoring
precision (79%, w 0.6, W 0.6) was used. Similarly, a higher level of inter-observer agreement
was found when two additional assessors applied half- (94%, w 0.6, W 0.7) rather
than full-unit scores (93%, w 0.4, W 0.4). Consequently, the effect of a brief re-calibration
exercise on the between-observer agreement for the assessment of full-unit body condition
scores (BCS) was examined. Prior to the exercise, the paired agreement between two
assessors and the trainer ranged from 68 to 78%, w 0.3–0.5, and W 0.4–0.5. Following
the re-calibration exercise, the level of inter-observer agreement increased to 75–93%, w
0.4–0.7, and W 0.4–0.6. No significant effect of assessor bias was found (p > 0.05). However,
most sample sheep were identified within the mid-range of body condition (BCS 2–3),
which affected the analysis and interpretation of reliability data. Overall, the results suggested
that trained and experienced assessors reliably scored the body condition of sheep
using both half- and full-unit scores, and that a period of re-calibration may offer a feasible
means of maintaining the consistency of cross-farm assessments performed by different
assessors.
