Follicular dynamics during the oestrous cycle in dairy goats

Development of all follicles with antral diameter greater than or equal to 2 mm during the oestrous cycle was characterized in goats of the Murciana-Granadina dairy breed by daily transrectal ultrasonography. Of nine does initially synchronized in oestrus, six returned to oestrus and three did not. In the first six does, mean cycle length was 21.2 (s.e. 2.3) days. There were mean total numbers of 6.2 (s.e. 0.6) small (2 to 3 mm), 1.9 (s.e. 0.3) medium (4 to 5 mm), and 1.0 (s.e. 0.2) large follicles (greater than or equal to 6 mm) each day but only numbers of large follicles differed with day of cycle (P < 0.01). The diameters of the largest follicle (LF1), the second largest (LF2) and the remaining follicles (RF) varied with day of cycle (P < 0.01). The LF1 and LF2 varied with day in similar patterns but the difference in diameter between them (P < 0.05) was greatest on days 7 and 9 (2.3 mm) and days 19 to 23 (2.2 to 3.8 mm), and least on days 2, 15, 16 and 18 (0.5 to 0.8 mm). The relationship between the LF1 and LF2 to the RF differed only early or late in the cycle when concentrations of progesterone were low (P < 0.05). There was same evidence to support follicular growth in waves. Although the number of apparently new follicles detected (4.8 (s.e. 0.4) per day) did not vary with day of cycle, follicles emerging at 3 mm over a 48-h period that grew to a diameter of greater than or equal to 6 mm were distributed non-randomly in three of six cyclic does. The three cystic does that did not return to oestrus by day 25 had large follicles (16 to 28 mm), fewer new follicles (3.3 (s.e. 1.1) per day; P < 0.01) than cyclic does (4.8 (s.e. 0.4) per day) and fewer follicles that became largest (4.0 v. 8.8 in cyclic does; P < 0.01).