Abstract
The efficacy and clinical safety of chlormadinone acetate (CMA) in preventing estrus were assessed in queens on condition that CMA was subcutaneously implanted in silastic silicon rubber. Thirteen queens were divided into the following four groups according to dose of CMA-administered: group 1 (n=3), control; group 2 (n=3), 2.5 mg/kg; group 3 (n=3), 5 mg/kg; group 4 (n=4), 20 mg/kg. The implants were left in these queens for 12 months after implantation. All control animals showed signs of estrus during the experiment, with periods of anestrus of normal duration. In contrast, estrus was completely inhibited in the CMA-treated groups. Plasma concentrations of CMA had started to decrease by l month after implantation and continued to decrease gradually thereafter. Histopathologically, the uterus from group 4 had coiled branched glands with little secretion in the endometrium. Mammary glands from the CMA-treated groups showed mild lobular development with acinar proliferation and secretion. Sections through the other organs (pituitary gland, adrenal gland, ovary, and implant site) had no distinct or consistent changes that could be related to the CMA-treated. It was concluded, therefore, that low, stable levels of CMA maintained in plasma by subcutaneous implantation could be the main reason for few changes due to the antigonadotropic and glucocorticoid-like activities and less serious condition in the uterine and mammary glands due to progestagenic activity.
