Estimation of Pubertal Mammary Development in Heifers by Computed Tomography

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Abstract
Computed tomography scanning is introduced as a new technique to quantify parenchymal tissue of heifer mammary glands. Tissue types with different densities attenuate x-rays differently, and computed tomography is based on computer processing of such x-ray attenuation data. Different tissue types can be quantified by summation of defined X-ray attenuation data. Parenchymal tissue was quantified in mammary glands from 25 heifers by computed tomography as well as by dissection and chemical analysis. Parenchymal tissue amounted to 455 g when measured by dissection and 106 cm3 when measured by computed tomography. This difference is related to the ability of computed tomography to exclude extraparenchymal tissue from the estimate. Computed tomography estimates of parenchymal tissue were more closely correlated with amount of fat-free parenchyma than with total parenchyma weight. This suggests that estimates obtained by computed tomography have less variation than estimates obtained by dissection due to the ability of computed tomography to exclude extraparenchymal tissue. Use of computed tomography furthermore eliminates the element of subjectivity present in methods that include dissection. It is concluded that computed tomography can provide reliable estimates of parenchymal tissue of heifer mammary glands.