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To clarify the effect of lactation period on ovarian follicular activity and associated hormonal levels in goats, six goats were monitored daily by ultrasonographic examination with blood sampling during early (Days 5 to 25; Day 0 was the day of kidding) and late (Days 40 to 60) lactation. While the presence of a corpus luteum of pregnancy retarded follicular growth in the ipsilateral ovary until Days 11-13 postpartum, the total follicular number (TFN) and area (TFA) increased during late lactation due to the significant increase in the number of medium- and large-sized follicles and decrease in the number of small follicles. Four goats showed a similar pattern of follicular development during the period studied characterized by the emergence of five and six waves during the early and late lactation, respectively. The largest follicle diameter of the first three waves monitored during early lactation was significantly smaller as compared with the diameter of those existing during late lactation. TFN showed a positive correlation with FSH but showed a negative correlation with immunoreactive (ir-) inhibin and estradiol during the postpartum period. TFA was positively correlated with ir-inhibin, estradiol and PRL and negatively correlated with FSH during the monitored periods. The plasma levels of ir-inhibin and progesterone were significantly higher during late lactation compared with the levels recorded during early lactation. Ir-inhibin levels showed a significant positive correlation with LH and estradiol during early and late lactation but showed a negative correlation with FSH during the whole lactation period. LH was positively correlated with estradiol and PRL during early and late lactation, respectively. These results suggest that the lactation period has a detrimental effect on ovarian activity during the early postpartum period in goats.

The current study was performed to follow up the circulating hormonal changes and to correlate the findings with the physiological activity of the corpus luteum (CL) and placenta during pregnancy in goats. Blood samples were collected weekly from five goats during pregnancy for measuring steroid and protein hormones. A gradual increase was observed in immunoreactive (ir-) inhibin, with maximal levels at the 17th week. The plasma concentrations of estradiol and prolactin (PRL) showed nearly similar patterns during pregnancy, where they declined to basal levels during the first 4 weeks post-breeding and then increased significantly, with the maximal concentration during late pregnancy. The plasma FSH and LH concentrations were maintained at basal levels throughout the gestation period. The plasma progesterone concentration abruptly increased in the first week post-breeding and remained at high values throughout the pregnancy period. Immunohistochemical localization of inhibin alpha, beta(A), beta(B) and steroidogenic enzymes cytochrome P450 aromatase, 3alpha-hydroxysteroid dehydrogenase (3betaHSD), cytochrome 17alpha-hydroxylase P450 and cholesterol side-chain cleavage cytochrome P450 in the cyclic and pregnant goat CL revealed positive immunoreactivity without affinity differences between the luteal and pregnancy stages. The placental syncytiotrophoblasts also showed positive staining, except for inhibin beta(A) and 3betaHSD. The giant binucleate cells of the placenta showed positive immunoreactions to PRL. These results suggest that the high concentrations of ir-inhibin, estradiol and PRL during late pregnancy are of placental origin and that the placenta may have a vital role in the maintenance of pregnancy, regulation of mammary growth and preparation for kidding and lactation in goats.

The present study was conducted to characterize follicular development and its hormonal control during early pregnancy in goats. The ovaries of goats (n=8) were scanned daily for follicles (> or = 2 mm in diameter) and corpora lutea by transrectal ultrasound with blood sampling from the jugular vein for monitoring the hormonal changes during the first thirty-five days after mating. During early pregnancy, three (37.5%), four (50%) and one (12.5%) goat showed nine, eight and seven waves of follicular development, respectively. The corpora lutea were detected as early as Day 3.61 ± 0.45 (7.47 ± 0.43 mm) of pregnancy (Day 0=day of mating) and attained their maximal cross-sectional diameter (10.64 ± 0.37 mm) on Day 25.7 ± 0.8 of pregnancy, respectively. A transient rise in FSH levels was temporally associated with the day of follicular wave emergence (up to three days prior to wave emergence). The plasma LH and estradiol levels were negatively correlated with the progesterone concentration. The rise in plasma immunoreactive (ir) inhibin levels was negatively correlated with the FSH concentration and positively correlated with the number of large-sized follicles. Alternatively, the mean plasma ir-inhibin levels showed a noticeable decline with the progression of pregnancy. The present results demonstrated that follicular development during early pregnancy shows a wave-like pattern, with seven to nine waves developing until Day 35 after breeding, and that the number of follicular waves can be predicted by the number of FSH peaks. The current study also demonstrated that the role of inhibin as an FSH regulator is maintained throughout early pregnancy.

The aim of the current study was to clarify the physiological role of inhibin in controlling FSH secretion and follicular development during the early pregnancy in goats. Eight goats investigated sonographically on Days 19–21 (Day 0 = day of mating) for pregnancy were assigned into control (n = 3) and treated (n = 5) groups. The ovaries of all animals were daily scanned with ultrasound for follicles 2 mm or more in diameter from 1 day before to 5 days after treatment. On Day 25 postbreeding; animals received either 10 ml, of normal goat serum or antiserum against [Tyr (30)]-inhibin alpha (1–30). Jugular blood samples were collected every 6 h starting 24 h before and until 120 h after treatment. The plasma concentration of FSH increased at 6 h and remained at significantly high levels until 120 h in treated vs. control group. The plasma concentrations of estradiol showed a marked increased at 66 h, with peak levels at 120 h after treatment of antiserum. The basal concentrations of LH and the pattern of plasma concentrations of progesterone were not significantly different between the two groups. The number of medium size (3.5–5.0 mm) follicles increased considerably from Day 2, whereas small (3.5 mm or less) and large (5 mm or more) follicles increased noticeably from Day 3, as compared with pre-treatment and controls. These results clearly indicated that inhibin is a key hormone in regulation of follicular development through regulation of endogenous FSH secretion during early pregnancy in goats.