Plasma progesterone concentrations in heifers and cows treated with a new intravaginal device

Abstract

A new form of intravaginal device (CIDR), manufactured by high temperature injection moulding and containing 1.9 g of progesterone in a silicon elastomer, was used in five trials with 101 cycling heifers, 11 ovariectomized (ovx) heifers and six cycling cows. The average plasma progesterone concentrations (PPC) during the 12 days of treatment with a CIDR device in ovx heifers was 5.6 (± 0.1) ng ml −1 and ranged from 8.7 (± 0.3) ng ml −1 6 h after inserting the device to 2.5 (± 0.2) ng ml −1 at removal. The average increase in PPCs 24 h after CIDR insertion (Treatment Day 1 equals TD 1) was 6.7 (± 0.4) ng ml −1 in ovx heifers compared to 4.9 (± 0.2) ng ml −1 in other cycling heifers ( P < 0.01). This varied from 3.9 ng ml −1 for devices inserted in pro-oestrus to 5.8 ng ml −1 for mid-cycle insertions ( P < 0.01). PPCs in ovx heifers were maintained at levels equivalent to those found in dioestrous heifers for the first three days after device insertion only. If a CIDR device was inserted during metoestrus (Cycle Days 2 or 3; oestrus equals Cycle Day 0) the average PPCs did not change significantly from 5.0 ng ml −1 on TD 1 with values of 5.3 ng ml −1 and 5.9 ng ml −1 recorded on TD 7 and TD 12, respectively ( P < 0.10). The concurrent treatment of some of these heifers with 10 mg oestradiol benzoate (OB), either in a gelatin capsule placed in the grooved surface of a CIDR device before insertion, or by i.m. injection significantly reduced PPCs on TD 7 (4.8 vs. 6.2 ng ml −1; P < 0.01) and TD 12 (5.0 vs. 7.9 ng ml −1; P < 0.01). Device insertion during metoestrus for 12 days significantly reduced oestrous cycle length compared to contemporary control animals (18.2 vs. 21.0 days; P < 0.001). Dioestrous heifers which had CIDRs inserted on Cycle Days 9 to 12 for four days had PPCs increased by 5.8 ng ml −1 on TD 1 (8.7 to 14.5 ng ml −1). The average decline in PPCs by 24 h after device removal was 4.5 ng ml −1, but this decline was significantly greater in those heifers which had CIDRs removed on Cycle Day 16 (7.7 ng ml −1; P < 0.01). CIDR-treated dioestrous heifers which were injected with a luteolytic dose of prostaglandin F 2α either 18 h before, or two days after CIDR insertion had similar average PPCs to ovx heifers at TDs 7 and 12 (3.2 and 2.7 ng ml −1). The average PPC in three cows treated with three CIDR devices for 15 days was three times higher than that in three cows treated with one device (8.4 vs. 2.8 ng ml −1; P < 0.01). In summary, these studies showed that changes in PPCs following insertion or removal of a CIDR device were influenced by the stage of treatment, the type of animal (ovx vs. cycling), the stage of cycle when treatment was initiated or terminated, the number of devices inserted, and concurrent treatment with oestrogen or prostaglandin F 2α.