The effect of zeranol implantation on some endocrine glands and gonads in fat-tailed lambs.

The present work was carried out to study the effect of zeranol on the pars distalis of 39 male fat-tailed lambs about 8 months old. The examined animals were classified into 3 groups. The group I was considered as control, group II and III were implanted subcutaneously in the back side of ear with 3 doses each of 12 mg zeranol at 40 - days intervals. Groups I and II were fed on concentrate mixture containing 70.45% starch and 14.42% digestible protein, while that of the group III containing 70.44% starch value and 7.92% digestible protein. Zeranol implants have been shown to increase body weight of animals group II and III. A significant difference was found in the number of the pars distalis cells as well as the histochemical changes in their properties have been observed in zeranol implanted lambs. The STH-cell showed a significant increase in number and signs of cellular hyperactivity. The ICSH-cells, FSH-cells and TSH-cells were significantly decreased in number and exhibited signs of less activity compared with the propriate cells of the nonimplanted animals. It is concluded that Zeranol improve gain, stimulate STH-cells and inhibit the GTH-cells as well as TSH-cells in the pars distalis of zeranol implanted animals.