Body condition influences maintenance of a persistent first wave dominant follicle in dairy cattle.

摘要

The objective of this study was to determine the effects of body condition and plasma progesterone concentration on the development of a persistent 1st wave dominant follicle after regression of the corpus luteum. Eight non-lactating dairy cows in high or low body condition (BC) were treated on day 7 of the oestrous cycle (day 0 = oestrus) with PGF2alpha and a used controlled internal drug releasing (CIDR) device containing progesterone (1.2 g) was inserted into the vagina until ovulation or day 16. Plasma was collected for progesterone and oestradiol determination from day 5 to day 18 (or ovulation), and ovarian follicles were monitored daily by ultrasonography. Plasma progesterone concentration was higher in high than in low BC cows between days5 and 7 (4.6 vs. 3.4 ng/ml; P<0.04). All low BC cows maintained the 1st wave dominant follicle and ovulated after removal of the CIDR device (18.3±0.3 days for 3 of the 4 cows; the 4th animal lost the CIDR device on day 11 and ovulated on day 15), whereas in the high BC cows ovulation occurred during the period of CIDR exposure (11.3±0.3 days for 3 of the 4 cows; the 4th cow developed a luteinized 1st wave dominant follicle that did not ovulate throughout the experimental period). Mean day of oestrus was 17 and 10 for low and high BC cows respectively. Plasma oestradiol concentration was high in low BC cows between days 8 and 17 (12.9±2.8 pg/ml), indicating the presence of an active persistent 1st wave dominant follicle. The regression of plasma progesterone concentration (Y) on day of cycle (X) was different in low and high BC animals: for low BC, Y = 19.9 - 3.49X + 0.166X2; for high BC, Y = 37.3 - 7.04X + 0.340X2. Although progesterone concentration was greater in high BC cows prior to day 8, a greater clearance of plasma progesterone released from the CIDR device in the absence of a corpus luteum altered follicular dynamics, leading to premature ovulation in the high BC cows. A greater basal concentration of progesterone was sustained in low BC cows that permitted maintenance of a persistent 1st wave dominant follicle.