Contributions of Maternal Serum Progesterone and Estradiol Concentrations or Corpora Luteal and Fetal Number to Mammary Growth and Development of Ewes During Pregnancy

Abstract

Sixteen ewes with similar weight and age were used in an experiment, and injected twice with PGF2 before being bred. Number of corpora lutea was detennined 5 d afier the onset of estrous cycle by laparoscopy. Number of ewes having 0, 1, 2, 3, and >3 corpora lutea were 3, 2, 5, 4, and 2, respectively. At parturition date, the number of ewes gave birth to 0, l, 2, 3, and 4 lambs were 3, 6, 4, 2, and 1, respectively. Blood samples were collected every other week during pregnancy for
progesterone and estradiol analyses with radioimmunoassay. At parturition date, the experimental ewes were sacrificed and the manunary glands were excised for detemiination of dry-fat-free tissue (DFFF). Multiple regression and correlation
was used to detemtine the relationships of scmm progesterone and estradiol concentrations and of corpora luteal and fetal number with mammary gland DFFT. The results of the experiment showed that the increased progesterone and estradiol concentrations during pregnancy simultaneously contributed 46.3% to the increased mammary gland DFFT at parturition (P< 0.05). The increased concentrations of progesterone or estradiol alone contributed 46.13% (P < 0.01) and 28.98% (P<0.05), respectively, to the increased mannriary gland DFFT. Both the number of corpora lutea and fetus simultaneously contributed 47.0% to the increased mammary gland DFFT (P<0.05). Number of corpora lutca or fetus alone contributed 46.4 (P<0.01) and 39.0% (P<0.01), respectively, to the increased mammary gland DFFT. lt was concluded that the increased niunber of corpora lutea and fetus, through their effects on manunogenic homloncs secretions, markedly increased mammary gland growth and development during pregnancy.