Semester

Spring

Date of Graduation

2007

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

E. Keith Inskeep.

Abstract

Pregnancy failures during placentation in lactating dairy cows have been associated with low concentrations of peripheral serum progesterone (P 4) and poor development of the chorioallantoic membranes. Experiment I was done to determine if pregnant cows with high or low concentrations of serum P4 differed in luteal production of P4 and/or clearance of injected P4. Luteal tissue was removed from pregnant cows with ≥ 4.0 ng/mL (High) or ≤ 2.5 ng/mL (Low) serum P4 during d 28 to 34 post-insemination. Luteal tissue was assayed for P4 by radioimmunoassay and for expression of mRNA for preproendothelins 1 and 3, endothelin converting enzyme, endothelin receptors A and B, cyclooxygenase-2, aldoketoreductase 1B5, 15-hydroxyprostaglandin dehydrogenase, and prostaglandin E synthase by real-time RT-PCR. Dispersed luteal cells were incubated for 2 h with bovine luteinizing hormone (bLH) or arachidonic acid (AA), increasing (10 -10 to 10-7 M) concentrations of endothelin-1 (ET-1), and combinations of ET-1 and bLH or AA. Neither luteal content of P4 (mean 106 +/- 12 mug) nor mRNAs for the endothelin or prostaglandin systems differed with serum P4 at lutectomy. Both basal and LH-stimulated secretion of P4 from dispersed luteal cells were inhibited (P < 0.05) by ET-1 in a dose dependent manner. Inhibition by ET-1 was greater (P < 0.05) for luteal cells from Low vs. High cows when incubated with AA. Both basal and AA-stimulated secretion of PGF 2alpha by luteal cells were increased by ET-1 in a dose-dependent manner. Basal and AA-stimulated 6-keto-PGF1alpha were decreased by ET-1 in a dose-dependent manner. To evaluate clearance of P4, cows were injected s.c. with 150 mg P4 every 12 h beginning at lutectomy. In jugular blood collected every 4 h until h 48, serum P4 was maintained at lower (P < 0.05) concentrations for Low vs. High cows. Area under the curve was less (P < 0.05) for Low (49.6 +/- 6.2) vs. High (83.6 +/- 12.5) cows. On the basis of these data, differences in clearance were more important than differences in luteal production to determine peripheral concentrations of P4. However, incubation with ET-1 and AA caused a greater reduction of P4 production for luteal cells from cows with Low than High serum P4. Thus, CL of Low cows might be more sensitive to luteolytic influences than CL of High cows. Reduced clearance of P4 might decrease late embryonic or early fetal mortality as efficiently as supplementation with exogenous progestogens. The objective of experiment II was to characterize the timing of detection of the allantois and diameter of the allantoic lumen, in dairy cows and heifers with embryos developed entirely in vivo, to determine whether these variables might be used to investigate late embryonic/early fetal loss. Reproductive tracts of dairy heifers (n = 33) and lactating dairy cows (n = 30) were examined daily, via transrectal ultrasonography (Aloka 900), beginning on d 21 post-insemination (PI). Variables included: first day of detection of the allantois, diameter of the allantoic lumen, length of the embryo at first detection of the allantois, and pregnancy retention on d 60 PI. Range and mean of first day of detection of the allantois (d 21 to 26, mean = 23 +/- 0.18 PI) agreed with previous reports. The allantois was detected earlier (P < 0.05) in heifers (22.4 +/- 0.2 d) than in cows (23.6 +/- 0.2 d). Diameter of the allantoic lumen at first detection (4.6 +/- 0.3 mm) did not differ with day of detection and was not affected by age of dam. In contrast, length of embryo (range 2.6 to 7.9 mm) varied with day of first detection of the allantois (P < 0.05), but not with age of dam. Pregnancy failure by day 60 PI did not differ with age of the dam. Differences in failure for pregnancies in which the allantois was detected earlier (≤ d 23 PI) or later (≥ d 24 PI) approached significance (P = 0.08) with those detected earlier failing more frequently than those detected later. Differences in day of first ultrasonographic detection of placental membranes, between heifers and cows, might reflect differing developmental rates and, based on present data, asynchrony in development of the embryo and the placental membranes might occur in some animals. Therefore, day of detection of the allantois might be useful for predicting survival or loss of pregnancy during placentation.

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