A quantitative analysis of mammary glands of dairy heifers reared at different rates of live weight gain.

The mammary glands of conventionally reared cows, never exceeding a live weight gain (LWG) of 0.74 kg/d, weighed 39% more and contained 68% more secretory tissue than glands of rapidly reared animals grown at 1.1 kg/d. In 11-month-old heifers reared at 3 rates of LWG (L, 0.57; M, 0.76 and H, 1.18 kg/d) gland weight was related to LWG, but dissected mammary parenchyma was heavier in animals on treatment L than on treatment H and followed a quadratic relationship. Parenchymal composition on treatment H was correlated to both age and body weight at puberty. No similar trend was observed in treatments L and M although group L animals had more ductal tissue and less fat than those of group M. Heifers from treatment L were reared during pregnancy at either 0.68 or 0.84 kg/d LWG (treatments LL and LH respectively) and heifers from treatment H at 0.58 kg/d (treatment HL). Total gland weight was unaffected by treatment, but the percentage by weight of secretory tissue in the gland in treatment HL was less than for treatments LL and LH. These experiments confirm that mammary development is permanently impaired by high rates of LWG in the first year of life. There was no impairment of mammary development in heifers reared moderately in the first year and more rapidly during pregnancy.

Differences in the biotransformation of a 17 beta-hydroxylated steroid, trenbolone acetate, in rat and cow.

1. The metabolism of trenbolone acetate, 17 beta-acetoxyestra-4,9,11-trien-3-one (TBA), an anabolic compound used as a growth promoter, was compared in rat and cow. 2. [6,7-3H] TBA was injected i.v. into rats and a heifer, and bile was collected for 24 h. In both species, the bile was the major route of excretion. TBA undergoes an extensive hydrolysis to 17 beta-hydroxyestra-4,9,11-trien-3-one and the unchanged compound was not detected, but subsequent major metabolic pathways are different in the two species. 3. In the rat, oxidation of the 17 beta-hydroxyl to the 17-oxo group and hydroxylation in the 16 alpha-position are the major routes. The three major metabolites are 17 beta-hydroxyestra-4,9,11-trien-3-one, 16 alpha, 17 beta-dihydroxyestra-4,9,11-trien-3-one and 16 alpha-hydroxyestra-4,9,11-trien-3, 17-dione. 4. In the heifer, 17 alpha-epimerization is the major pathway and the main metabolite is the 17 alpha-hydroxyestra-4,9,11-trien-3-one. 5. In both species, estra-4,9,11-trien-3,17-dione and the other metabolites, resulting either from hydroxylation in 1, 2, 6 beta, 16 alpha or 16 beta positions, or from aromatization of the A ring, were minor products. 6. Overall, 60% of the 3-oxotriene structures identified in the rat bile were 17 beta-hydroxylated and the remainder were 17-keto metabolites, whereas in the heifer bile 90% were 17 alpha-hydroxylated compounds. 7. Thus, in bovine species, the major pathway is similar to those of testosterone or 17 beta-estradiol which are mainly excreted as their 17 alpha-epimers. The epimerization strongly decreases the biological potency, as with the natural 17 beta-hormones, and leads to detoxication of tissue residues.