177 Periparturient olive oil supplementation increases oocyte yield in dairy cows

Negative energy balance (NEB) in dairy cows, which is characterized by high levels of nonesterified fatty acid (NEFA), has been related to reduced fertility. Saturated NEFAs are associated with reduced oocyte competence, which is counteracted by oleic acid (C18:1) in follicular fluid and protection of cumulus cells (Aardema et al. 2017 Biol. Reprod. 96, 982–992). Oocytes presumed to be fertilized at 60–100 days postpartum likely began their development during the NEB period, which may affect their quality. During the NEB period, follicles are exposed to high levels of saturated palmitic (C16:0) and stearic acid (C18:0) via blood (Aardema et al. 2013 Biol. Reprod 88, 164). The Britt hypothesis postulates that NEB affects fertility via a negative impact on follicle and oocyte quality (Britt et al. 1992 Bov. Proc. 24, 39–43). The current study investigated whether periparturient C18:1-rich olive oil fat supplementation counteracts potential negative effects on oocytes during NEB. Pregnant HF heifers (age 2 years) were pseudo-at-random divided based on body condition score and individually received a mixed standard ration (dry matter intake measured daily) for dry or lactating cows with a rumen-protected standard fat supplement rich in C16:0 (CTR; Milkpower, ForFarmers®, 78.8% C16:0, n = 5) or C18:1 (OA; Monofat, Schils®, 62.9% C18:1, n = 6) from 4 weeks before (−4 weeks) until 4 weeks postcalving (pc; +4 weeks). Lipidomic and NEFA analysis (measure NEB) was performed on serum samples of −4 weeks (t = 0), −2, +2, and +6 weeks pc by HPLC-mass spectrometry. At +8, +12 and +16 weeks pc, after a 20-µg GnRH treatment, cumulus–oocyte complexes (COCs) were collected two times with a 5-day interval from 3- to 12-mm follicles by transvaginal ovum pickup (OPU). Collected COCs were in vitro matured, followed by IVF and embryo culture until Day 8, according to our standard protocol. Several oocytes were analyzed with a Poisson distribution and developmental competence with a logistic regression model, Akaike’s information criterion was used for model reduction to calculate 95% profile (log) likelihood confidence intervals. The study was approved by the ethics committee. At −2 weeks and +2 weeks, there was a major difference in the blood fatty acid composition in the OA group compared with the CTR. There was a lower level of C16:0 (~25%) and higher levels of C18:0 (~42%) and C18:1 (~25%) in the OA group compared with the high level of C16:0 (~60% at −2 weeks and ~45% in +2 weeks) and low level of C18:0 (~25%) and C18:1 (~15%) in the CTR. Interestingly, the number of collected COCs by OPU was 1.6 times higher in the OA (P < 0.05) than in the CTR group (13.1 ± 6.8 and 8.2 ± 4.0, respectively), but oocyte competence measured via cleavage and blastocyst number did not differ between groups. Fat supplementation significantly affected the lipid profile in blood, resulting in high levels of C18:0 and C18:1 and low levels of C16:0 in the OA group versus the CTR. Furthermore, a significantly higher number of oocytes were collected during OPU. These data show that periparturient olive oil supplementation appears to increase oocyte yield, and potentially tempers the negative impact of NEB on developing follicles and their oocytes.