Nutrient Prioritization in Dairy Cows Early Postpartum: Mismatch Between Metabolism and Fertility

For several decades, researchers worldwide report a decrease in fertility in high-yielding dairy cows, most probably based on conflicting metabolic and reproductive needs. The dairy herd manager's success at improving milk production has been accompanied by a negative trend for the most visible reproductive parameters such as calving intervals, number of days open and number of inseminations needed per pregnancy. In parallel, many research groups studied the metabolic and endocrine factors that influence follicular growth and the developmental competence of oocytes and embryos. In the past, herd managers and reproductive biologists each tried to tackle the same problems with limited consultation. More recently, the situation has improved significantly and theriogenologists, nutritionists and veterinarians now conduct research in multidisciplinary teams. This review paper starts in a general way by discussing nutrient prioritization towards the udder to guarantee milk production and by describing interactions between the somatotropic and gonadotropic axis. It then focuses on the consequences of the negative energy balance on follicular growth and environment, oocyte and embryo quality, not only by summarizing the currently accepted hypotheses but also based on clear scientific evidence at the follicular level. All this, with one question in mind: is there a mismatch between metabolism and fertility and what can the dairy manager learn from research to tackle the problem of reduced fertility

Elevated non-esterified fatty acid concentrations during in vitro maturation affect the transcriptome profile of day 14 bovine embryos 7 days after transfer

We showed earlier that exposure to elevated non-esterified fatty acid (NEFA) concentrations during in vitro oocyte maturation (IVM) affects post-hatching development of day (D) 14 bovine embryos (Desmet et al., Anim. Reprod. 14,p947,2017). Lipotoxic conditions during IVM influence DNA methylation in the D7 embryo and may thus affect its transcriptome during later development. Therefore the aim was to analyse the transcriptome profile of D14 embryos to investigate which mechanisms mediate carryover effects of adverse maturation condition on post-hatching development. Bovine oocytes were matured for 24h under 2 conditions: 1) basal physiological NEFA conditions (BAS; 28μM stearic acid (SA), 21μM oleic acid (OA), 23μM palmitic acid (PA)); and 2) high PA concentration (most predominant in follicular fluid during negative energy balance) (HPA; 150μM PA, 28µM SA, 21µM OA). After fertilization, zygotes were cultured in SOF with serum. 8 blastocysts (normal and expanded, equally distributed per treatment and per replicate) were transferred to healthy non-lactating Holstein Friesian cows at D7 (n = 8, 5 replicates). Each cow was used once for each treatment in a cross-over design. After transcervical recovery, D14 concepti (n = 45) were dissected into embryonic disc (ED) and extra-embryonic tissue (EXT). ED (n = 11BAS/7PA) and EXT (n = 13BAS/8PA) were subjected to RNA sequencing (without RNA amplification). Differential expression was established in a DESeq2 model based on Negative Binomial distribution. Samples were divided by sample type for further analysis. A false discovery rate (FDR) of 10% was used as cut-off for differentially expressed genes (DEG) and P-values were Benjamini-Hochberg corrected. Ingenuity Pathway Analysis (IPA) and Gene Set Enrichment Analysis (GSEA) were performed. Recovery rate at D14 was not significantly different between treatments. Within ED and EXT datasets, only 14 and 0 DEGs were detected in HPA embryos compared to BAS embryos, respectively. However, when comparing concepti of similar morphological class (spherical/ovoid/tubular) and sex, higher numbers of DEGs could be detected (e.g. in ED dataset up to 6 times more DEGs). Overall, more DEGs were observed in ED compared to EXT at each morphological stage (except male tubular embryos). IPA and GSEA showed that affected pathways were related to cell growth and adhesion, metabolism, endoplasmic reticulum stress, mitochondrial respiratory chain complex and epigenetic mechanisms. To conclude, elevated PA exposure during IVM has carryover effects on the transcriptome profile of D14 concepti although only good quality D7 embryos with the same morphology have been transferred. D14 transcriptome patterns were dependant on morphology (elongation stage) and cell type (ED versus EXT) but common pathways affected were related to cellular development, metabolism and epigenetics. This suggests that metabolic stress during oocyte maturation may have longlasting effects on embryo development that may lead to reduced fertility in high-yielding dairy cows

Elevated non-esterified fatty acid concentrations hamper bovine oviductal epithelial cell physiology in three different in vitro culture systems

Elevated non-esterified fatty acids (NEFAs) have been recognized as an important link between lipolytic metabolic conditions and impaired fertility in high-yielding dairy cows. However, NEFA effects on the oviductal micro-environment currently remain unknown. We hypothesize that elevated NEFAs may contribute to the complex pathology of subfertility by exerting a negative effect on bovine oviductal epithelial cell (BOEC) physiology. Therefore, the objectives of this study were to elucidate direct NEFA effects on BOEC physiology in three different in vitro cell culture systems. Bovine oviductal epithelial cells (four replicates) were mechanically isolated, pooled, and cultured as conventional monolayers, as explants, and in a polarized cell culture system with Dulbecco’s modified Eagle’s medium/F12–based culture medium. Bovine oviductal epithelial cells were exposed to an NEFA mixture of oleic, stearic, and palmitic acids for 24 hours at both physiological and pathologic concentrations. A control (0 mM NEFA) and a solvent control (0 mM NEFA þ 0.45% ethanol) group were implemented. Bovine oviductal epithelial cells physiology was assessed by means of cell number and viability, a sperm binding assay, transepithelial electric resistance (TER), and a wound-healing assay. Bovine oviductal epithelial cell morphology was assessed by scanning electron microscopy on cell polarity, presence of microvilli and cilia, and monolayer integrity. Bovine oviductal epithelial cell number was negatively affected by increasing NEFAs, however, cell viability was not. Sperm binding affinity significantly decreased with increasing NEFAs and tended (P ¼ 0.051) to be more affected by the direction of NEFA exposure in the polarized cell culture system. The absolute TER increase after NEFA exposure in the control (110 11 U.cm2) was significantly higher than that in all the other treatments and was also different depending on the exposure side. Bidirectional exposed monolayers were even associated with a significant TER reduction (15 10 U.cm2; P < 0.05). Cell proliferation capacity showed a decreased cell migration with increasing NEFA concentrations but was irrespective of the exposure side. Bovine oviductal epithelial cell morphology was not affected. In conclusion, in an in vitro setting, NEFAs exert a negative effect on BOEC physiology but not morphology. Ultimately, these physiological alterations in its microenvironment may result in suboptimal development of the pre-implantation embryo and a reduced reproductive outcome in dairy cattle.Depto. de Producción AnimalFac. de VeterinariaTRUEpu