BODY CONDITION INFLUENCES MAINTENANCE OF A PERSISTENT FIRST WAVE DOMINANT FOLLICLE IN DAIRY-CATTLE

The objective of this study was to determine whether plasma concentrat ions of progesterone (P-4) from a controlled internal drug releasing ( CIDR) device (similar to 2 ng/ml) were adequate to sustain a persisten t first wave dominant follicle (FWDF) in low body condition (LBC, body condition score [BCS] 1 = lean, 5 = fat [2.3 +/- 0.72, n = 4]) compar ed with high body condition (HBC, BCS = 4.4 +/- 0.12, n = 4) nonlactat ing dairy cows. On Day 7 of the estrous cycle (Day 0 = estrus), cows w ere treated with PGF(2 alpha) (25 mg im Lutalyse,(R) P.M., and Day 8 A .M.) and a used CIDR device containing P-4 (1.2 g) was inserted into t he 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 ovar ian follicles were monitored daily by ultrasonography. Mean concentrat ions of plasma P-4 were greater in HBC than LBC cows between Days 5 an d 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 de vice (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 deve loped a luteinized first wave dominant follicle that did not ovulate d uring 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 LB C cows reflected presence of an active persistent first wave dominant follicle. The differential effect of BCS an concentrations of plasma P -4 (y = ng/ml) was reflected by the difference (P < 0.01) in regressio ns: 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 g reater 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 follicula r dynamics, leading to premature ovulation in the HBC cows. A greater basal concentration of P-4 was sustained in LBC cows that permitted ma intenance of a persistent first wave dominant follicle. (C) 1998 by El sevier Science Inc.