MMP-13 immunostaining. Representative sections and data of the deep zone of articular cartilage from placebo-treated and ASU-treated dogs (original magnification ×250). Morphometric analysis of MMP-13 immunostaining data are represented as box plot and were analyzed using Mann-Whitney two-tailed U-test. P ≤ 0.05 is considered statistically significant. ASU, avocado/soybean unsaponifiables; MMP, matrix metalloproteinase.