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

Abstract

The objective of this study was to determine whether plasma concentrations of progesterone (P 4) from a controlled internal drug releasing (CIDR) device (~2 ng/ml) were adequate to sustain a persistent first wave dominant follicle (FWDF) in low body condition (LBC, body condition score [BCS] 1 = lean, 5 = fat [2.3 ± 0.72, n = 4]) compared with high body condition (HBC, BCS = 4.4 ± 0.12, n = 4) nonlactating dairy cows. On Day 7 of the estrous cycle (Day 0 = estrus), cows were treated with PGF 2α (25 mg im Lutalyse, ® P.M., and Day 8 A.M.) and a used CIDR device containing P 4 (1.2 g) was inserted into the vagina until ovulation or Day 16. Plasma was collected for P 4 and estradiol (E 2) analyses from Day 5 to Day 18 (or ovulation), and ovarian follicles were monitored daily by ultrasonography. Mean concentrations of plasma P 4 were greater in HBC than LBC cows between Days 5 and 7 (4.6 > 3.4 ± 0.37 ng/ml; P < 0.04). All LBC cows maintained the first wave dominant follicle and ovulated after removal of the CIDR device (18.3 ± 0.3 d, n = 3; Cow 4 lost the CIDR device on Day 11 and ovulated on Day 15), whereas in the HBC cows ovulation occurred during the period of CIDR exposure (11.3 ± 0.3 d; n = 3; a fourth cow developed a luteinized first wave dominant follicle that did not ovulate during the experimental protocol on Day 19). Mean day of estrus was 17 ± 0.4 for LBC(n = 3) and 10 ± 0.4 for HBC (n = 3) cows. Sustained concentrations of plasma E 2 (12.9 ± 2.8 pg/ml; Days 8 to 17) in LBC cows reflected presence of an active persistent first wave dominant follicle. The differential effect of BCS on concentrations of plasma P 4 (y = ng/ml) was reflected by the difference (P < 0.01) in regressions: y LBC = 19.9 − 3.49x + 0.166x 2 vs y HBC = 37.3 − 7.04x + 0.340x 2 (x = day of cycle, Days 7 to 12). Although P 4 concentration was greater for HBC cows prior to Day 8, a greater clearance of plasma P 4 released from the CIDR device in the absence of a CL altered follicular dynamics, leading to premature ovulation in the HBC cows. A greater basal concentration of P 4 was sustained in LBC cows that permitted maintenance of a persistent first wave dominant follicle.