Bovine mammary gland development during gestation

Ten pairs of identical twin heifers were slaughtered at succes-sive two month gestation intervals to study mammary gland development during gestation. Gland composition showed trends of decreasing fat and DNA concentration and of increasing water, percent DFFT, RNA concentration and RNA/DNA ratio as gestation progressed into peak lactation. Udder, gland and DFFT weights, DNA g/gland and alveolar surface area all generally increased throughout gestation until parturi-tion but at peak lactation they had decreased. These results were supported by histological and gross appearance of the glands. Data from six pairs of identical twins were used to plot semilogarithmic regression lines of the parameter vs. time. Parameters investigated were; full trimmed udder weight, glands only weight, DFFT weight, DNA (mg/kg body weight), DNA (g/gland) and alveolar surface area. Their rates of change per month were: 10.8 percent, 22.0 percent, 30.5 percent, 25.3 percent, 24.0 percent and 30.0 percent, respectively. All param-eters measured indicated that bovine mammary gland growth during gesta-tion was continuous from conception to parturition and that no further development occurred up to peak lactation.