195 Vasoconstriction induced by ergot alkaloids affects oocyte developmental capacity in pregnant sheep

Previous work indicates that ergot alkaloid exposure (E⁺) from consumption of endophyte-infected tall fescue influences vasoactivity through serotonin receptors by acting as both an agonist and antagonist. The hypotheses for this trial were that vasoconstriction results in hypoxia, which is exacerbated by the demands of pregnancy, and hypoxia affects oocyte maturation. The objectives of this work were to study the effect of systemic vasoconstriction caused by E⁺ on the developmental capacity of sheep oocytes and to determine the potential role of 5-hydroxytryptophan (5-HTP) on the E⁺ effects. Suffolk cross ewes were synchronized in nine weekly groups and bred to a ram. Pregnancy was confirmed at Day 45 postbreeding, and on Day 80 for each weekly group, three ewes carrying twins were randomly assigned to one of three treatments (trt). Ewes were individually fed total mixed ration (TMR) starting on Day 80, and trt started on Day 86 until euthanasia on Day 112 as follows: (1) Control (TMR, no treatment); (2) E⁺ and 5-HTP (TMR + 1.77 mg E⁺ per ewe in fescue seed + 2.5 mg 5-HTP kg⁻¹ bodyweight); and (3) E⁺ (TMR + E⁺ in fescue seed). Carotid diameter was obtained by ultrasonography on Days 80, 90, 100, and 111. Ovaries were retrieved after euthanasia. Oocytes were collected by aspiration and placed into IVM medium (Stroebech IVM for Small Ruminants) at 38.5°C, 5% CO₂, in high humidity. At 24 h of IVM, oocytes were vortexed for 1 min to remove excess cumulus cells and stained with MitoTracker^TM Red CMXRos (MTR) to determine mitochondrial membrane potential (3 ewes × 4 reps = 12 ewes) or BioTracker ATP-Red (ATP) for intracellular ATP (3 ewes × 5 reps = 15 ewes). All oocytes were co-stained with Hoechst for nuclear maturation. For statistical analysis, each ewe was considered an experimental unit. A mixed model of repeated measures was used for carotid diameter over time: main effects of trt, time, and interaction, blocked by replicate. Only MII oocytes were used for MTR and ATP. A mixed model was used for each single endpoint with main effect of trt, blocked by replicate. Significance was set at P ≤ 0.05. Carotid diameter showed trt, time, and interaction effects: both E⁺ treatments presented a decrease in carotid diameter. Mean diameters for Days 80, 90, 100, and 111, as a ratio of Day 80, were 1^a, 0.99 ± 0.02^a, 1.02 ± 0.04^a, and 1.05 ± 0.03^a for trt 1; 1^a, 0.86 ± 0.05^b, 0.93 ± 0.03^c, and 0.97 ± 0.04^ac for trt 2; and 1^a, 0.84 ± 0.03^b, 0.92 ± 0.02^c, and 0.92 ± 0.02^c for trt 3 (a, b, c, d: P ≤ 0.05 within trt). Mean oocyte recovery rate was no different among groups at 15.15 ± 1.66 oocytes/ewe. Maturation rates showed a trt effect: 31.0 ± 10.2^a, 11.1 ± 4.4^b, and 14.5 ± 2.9^b MII oocytes/stained oocytes for trt 1, 2, and 3 respectively). Mean relative fluorescence units for MTR and ATP in mature oocytes were not different among trt. In this trial, E⁺-induced vasoconstriction and its systemic effects altered the developmental capacity of oocytes to reach nuclear maturation after IVM. The MTR and ATP levels, however, were not affected. Further research is needed in this area, considering that only a small number of mature oocytes were included in each bioenergetic analysis.