Assessment of luteal function in goats by ultrasonographic image attribute analysis

The aim of this study was to evaluate the potential of luteal echotexture (mean pixel value and heterogeneity), as a tool for assessing luteal function during different phases of the estrous cycle in Toggenburg goats. Sonographic evaluations of the ovaries were performed daily in nulliparous goats (n = 21), using a 5 MHz linear rectal probe, commencing at estrus (day 0). Blood samples were collected daily for plasma progesterone RIA and images recorded on VHS tape and then digitized in TIFF format at a resolution of 1500 × 1125 pixels. A representative elementary area (REA) of 5625 pixels (0.31 cm2) of these images was analyzed using custom-developed software, for mean pixel value and heterogeneity. Mean plasma progesterone, luteal area and pixels all reached maximum values at approximately days 13 and 14, during luteogenesis. Luteolysis was characterized by an abrupt decrease in blood progesterone concentration following ovulation, and a gradual decline in luteal area and pixel values. The luteal tissue area was positively correlated with plasma progesterone concentration during both luteogenesis (r = 0.63; P < 0.05) and luteolysis (r = 0.50; P < 0.05). Weak correlations were recorded between the mean pixel value and luteal tissue area during luteogenesis (r = 0.34; P < 0.05) and luteolysis (r = 0.26; P < 0.05). Similarly, weak correlations between the mean pixel value and plasma progesterone concentration were recorded during luteogenesis (r = 0.24; P < 0.05) and luteolysis (r = 0.37; P < 0.05). The pixel heterogeneity was not correlated with luteal tissue area or the plasma progesterone concentration at any stage of the estrous cycle. The results show the association between the corpus luteum echotexture and steriodogenic function to be weak and the present ultrasound technology, to have limited potential in evaluating luteal function in goats.