The In vitro development of bovine oocytes after maturation in glucose and β-hydroxybutyrate concentrations associated with negative energy balance in dairy cows

Negative energy balance (NEB) in high yielding dairy cows early postpartum may affect oocyte quality. Therefore, we tested the effect of two different beta-hydroxybutyrate (BHB) and glucose concentrations, which are associated with subclinical or clinical ketosis, during in vitro maturation (IVM) on the developmental competence of bovine oocytes. In Expt 1, subclinical ketosis conditions were imitated. Oocytes were matured in four different serum-free media with two glucose concentrations (g1 = 2.75 mM or G1 = 5.5 mM glucose) and with or without BHB (BHB1 = 1.8 mM BHB). Following maturation groups were used: g1, G1, g1 : BHB1 and G1 : BHB1. In Expt 2, clinical ketosis conditions were mimicked by using the concentrations: g2 = 1.375 mM or G2 = 3.1 mM glucose and BHB2 = 4.0 mM BHB. The combinations used were: g2, G2, g2 : BHB2 and G2 : BHB2. After IVM and in vitro fertilization (IVF), presumptive zygotes were routinely cultured for 7 days in synthetic oviduct fluid [SOF; 5% fetal calf serum (FCS)]. At 48 h and 8 days pi, cleavage rate and number of blastocysts were recorded respectively. The results demonstrated that the maturation conditions mimicking subclinical (g1 : BHB1) and clinical ketosis (g2 : BHB2) resulted in an impaired developmental competence of the oocyte after maturation. Especially the moderately low (g1) or extremely low glucose (g2) concentrations were responsible for this detrimental effect that was associated with a blocked cumulus expansion. Only in moderately low glucose conditions (g1 : BHB1), BHB exerted an additive toxic effect during oocyte maturation resulting in a reduced blastocyst rate. Conclusively, our results may suggest that subclinical and clinical ketosis can affect the oocyte's developmental competence most likely through a directly adverse effect of the low glucose concentrations on oocyte maturation. Only in subclinical conditions this harmful effect may be aggravated by BHB.