Profiles of prostaglandin F2α metabolite in dairy cattle during luteal regression and pregnancy: implications for corpus luteum maintenance†

Mechanisms of bovine corpus luteum (CL) maintenance during the second month of pregnancy have not been adequately investigated, despite significant reproductive losses. In the first month, interferon-tau is believed to suppress oxytocin-stimulated prostaglandin F2α (PGF) production, yet there are conflicting reports of circulating PGF metabolite (PGFM). In this study, characterization of PGFM and P4 occurred through continuous bihourly blood sampling in cows undergoing CL regression (day 18-21, n = 5), and during the first (day 18-21, n = 5) and second month (day 47-61; n = 16) of pregnancy. Cattle in the second month were assigned to control (n = 8) or oxytocin treatment (n = 8; three pulses to mimic luteolysis) to evaluate if oxytocin receptors were active. All cows but one (which had elevated PGFM prior to oxytocin treatment) maintained the pregnancy. Basal PGFM concentrations were low (11.6 ± 0.7 pg/mL) in the first month but increased 2.54-fold in the second month. Few (0.26 ± 0.12 pulses/day) PGFM pulses with low peak concentrations (28.8 ± 3.1 pg/mL) were observed during the first month of pregnancy, similar to cows not undergoing regression. However, in the second month, frequency (1.10 ± 0.26 pulses/day) and peak concentration (67.2 ± 5.0 pg/mL) of PGFM pulses increased, displaying similar frequency but lower peak PGFM than seen in regression (1.44 ± 0.14 pulses/day; 134.5 ± 18.9 pg/mL). Oxytocin treatment increased likelihood of PGFM pulses post-treatment and increased peak concentration (89.7 ± 10.1 pg/mL) in cows during the second month. Thus, cows have more PGFM pulses during second than first month of pregnancy, possibly induced by endogenous oxytocin, indicating suppression of PGF production is an important mechanism for CL maintenance during first but not second month of pregnancy.

Oxytocin-induced prostaglandin F2-alpha release is low in early bovine pregnancy but increases during the second month of pregnancy†

Circulating prostaglandin F2α metabolite (PGFM) after an oxytocin challenge was evaluated throughout the first 2 months of pregnancy in lactating Holstein cows. On day 11, 18, and 25 after artificial insemination (AI), and on days 32, 39, 46, 53, and 60 of pregnancy, cows were challenged with 50 IU oxytocin, i.m. Blood was collected before (0 min), 30, 60, 90, and 120 min after oxytocin for plasma PGFM concentrations. Ultrasound evaluations were performed for pregnancy diagnosis on day 32-60 post-AI. Nonpregnant (NP) cows on day 18 were designated by a lack of interferon-stimulated genes in peripheral blood leukocytes and Pregnant (P) based on day 32 ultrasound. On day 11, P and NP were similar with low PGFM and no effect of oxytocin on PGFM. On day 18, oxytocin increased PGFM (3-fold) in NP with little change in P cows. Comparing only P cows from day 11 to 60, basal circulating PGFM increased as pregnancy progressed, with day 11 and 18, lower than all days from day 25 to 60 of pregnancy. Oxytocin-induced PGFM in P cows on day 25 was greater than P cows on day 18 (2.9-fold). However, oxytocin-induced PGFM was lower on day 25 compared to day 53 and 60, with intermediate values on day 32, 39, and 46 of pregnancy. Thus, the corpus luteum (CL) of early pregnancy (day 11, 18) is maintained by suppression of PGF, as reflected by suppressed PGFM in this study. However, during the second month of pregnancy, uterine PGF secretion was not suppressed since basal PGFM and oxytocin-induced PGFM secretion were elevated. Apparently, mechanisms other than suppression of oxytocin receptors maintain CL after day 25 of pregnancy.

Variability of serum reproductive hormones in cows presenting various reproductive conditions in semi-arid areas of the North West Province, South Africa

Background and Aim:

Hormones play a significant role in supporting reproductive processes. Predisposition to metabolic disorders may result from biological alterations in the neurohormonal system, thus leading to impaired immune function and poor reproductive performance. The aim of this study was to determine the reproductive hormonal profile in cows with reproductive conditions in semi-arid areas of the North West Province, South Africa, to establish possible correlations between different conditions and the hormonal profile.

Materials and Methods:

Blood samples were collected from cows in different communal areas of Mafikeng. Convenience sampling was used to collect samples for the study. Blood samples were collected cows experiencing dystocia (n=50), retained placenta (n=13), downer cow syndrome (n=34), vaginal prolapse (n=16), and abortions (n=69), following cases reported at the Animal Health Hospital of the North-West University, Mafikeng Campus. Descriptive statistics, such as mean and standard deviations, were used to describe the distribution of hormone levels across reproductive conditions. p-value less than the significance level was set at 5% (p<0.05).

Results:

Data obtained revealed significantly higher estradiol in abortion (1122.99±71.99 pg/ml), downer cow syndrome (781.32±135.7 pg/ml), and dystocia (862.09±123.44 pg/ml). Oxytocin (OT) differed significantly in cows with dystocia (370.50±71.66 pg/ml) and abortion (574.73±60.65 pg/ml). Significantly low progesterone (Pg) was observed in abortion (2.45±1.509 ng/ml) and dystocia (8.59±0.402 ng/ml) while increased prostaglandin alpha was observed in cows with vaginal prolapse and abortion.

Conclusion:

The findings highlight an increase in serum estradiol and OT in aborting cows. Low Pg and estradiol in cows with vaginal prolapses and retained placenta were noted. An association was seen between downer cow syndrome and high concentrations of estradiol and Pg. Prostaglandin alpha may increase in cases of vaginal prolapse and abortion. Hormonal alterations were observed and may contribute to the incidences of different reproductive conditions.