Progesterone levels and days to luteolysis in mares treated with intrauterine fractionated coconut oil

Abstract

Intrauterine plant oil infusion, including fractionated coconut oil, has been previously found to be a safe, inexpensive, and reversible method of prolonging the luteal phase in mares when administered on Day 10 of the estrous cycle. Our objective was to understand the uteroovarian response to the administration of fractionated coconut oil infusion in the uterus of diestrous mares. We hypothesized that intrauterine coconut oil administration on Day 10 would prolong luteal life span in a dose-dependent fashion and would result in higher serum progesterone levels than untreated mares at the expected time of luteolysis. Light-horse mares (n = 18) were examined using transrectal palpation and ultrasonography to determine if they had a normal interovulatory interval and were then examined daily in estrus until the day of ovulation (Day 0) and then every other day during an estrous cycle. Jugular blood was drawn on Day 11, Day 13, Day 15, and Day 17, centrifuged, and serum stored until assayed for progesterone (P4; Siemens Coat-a-Count Progesterone RIA, Los Angeles, CA, USA). Mares were randomly assigned to treatment and studied over one to two estrous cycles with a rest cycle after each treatment cycle. Groups were: control (n = 5), fractionated coconut oil 1.0 mL (Miglyol 810; Sasol Oil, Witten, Germany) infused in the uterus with an artificial insemination pipette on Day 10 (Group 1; n = 5) and fractionated coconut oil 0.5 mL infused in the uterus with an embryo transfer gun, on Day 10 (Group 2; n = 5). All statistical analyses were performed using analytical software (Stata SE, version 13.1, College Station, TX, USA) at P < 0.05. Data were first evaluated using the Shapiro-Wilk test for normality. Differences between groups in days to luteolysis (DTL) were examined using analysis of variance and Bonferroni, and the effect of day and treatment on P4 levels were examined using the Kruskal-Wallis and Dunn's all pairwise test. There was a significant difference in DTL between the groups (P = 0.0083), with fewer DTL in Group 1 compared to control (P = 0.011) and to Group 2 (P = 0.034). There was a significant effect of day (P < 0.0001) on P4 levels with Day 11 P4 levels higher than Day 15 and Day 17 and Day 13 P4 levels higher than Day 15 or Day 17 (P < 0.03). There was a significant effect of treatment group (P = 0.0098) on P4 levels with control and Group 2 levels higher than Group 1 mares (P = 0.0012, P = 0.0495, respectively). We concluded that intrauterine administration of 1 mL of fractionated coconut oil lowered P4 levels in diestrus in a dose-dependent fashion and did not prolonged the luteal phase of the mares.

The effects of intrauterine infusion of peanut oil on endometrial health, salivary cortisol and interovulatory period in mares

“…[4,15,18,19]). It is also consistent with the recent work of Diel de Amorim et al [28], which failed to reproduce the results which Wilsher and Allen [24] obtained with coconut oil. Furthermore, since mares are known to undergo spontaneously prolonged luteal phases [40,41], it is possible that the prolonged interovulatory period in 2/6 mares was not actually caused by the oil treatment.…”

“…believed to be caused by the hyperechoic oil lining the endometrial folds (which were themselves not pronounced because the mares were in dioestrus) -was very similar in this study to that reported by Diel de Amorim et al [28]. The hyperechogenicity, distribution and volume of this pattern allowed it to be easily distinguished from non-oil, free fluid in the uterus.…”

“…Bacteriological culture of the oil was negative. This is consistent with the findings of Diel de Amorim et al [28], who cultured their coconut oil to rule out infection as a cause of treated mares undergoing shortened luteal phases, and also got negative culture results Diel de Amorim et al [28] reported a lymphoplasmocytic inflammatory cell infiltration and neutrophilic inflammation of the stratum compactum of the endometrium following intrauterine coconut oil infusion, with occasional eosinophils seen. The inflammatory response to intrauterine peanut oil infusion seen in this study was predominantly eosinophilic, with an increase in the number of eosinophils observed in the endometrium following…”

“…Anecdotally, peanut oil is being used in clinical practice as a method of oestrus suppression in mares, following the publication of the paper of Wilsher and Allen in 2011 [24]. However, a 2016 paper [28] showed that intrauterine coconut oil causes an inflammatory reaction in the endometrium, which raises the possibility that treatment with intrauterine plant oil can have a detrimental effect on endometrial health and subsequently future fertility. Furthermore, no studies have been reported assessing whether the intrauterine infusion of either coconut or peanut oil is painful for mares.…”

Coding RNA Sequencing of Equine Endometrium during Maternal Recognition of Pregnancy

“…Other experiments have infused coconut or peanut oil on day 10 of non-pregnant mares’ cycle and luteostasis was achieved [14]. This indicates that a component in the oil impacts the luteolytic pathway, but subsequent studies have failed to illicit the same response [15]. Research on MRP has evaluated transcriptional differences in the endometrium during and after MRP utilizing a microarray [16,17].…”