Administration of glycerol-based formulations in sheep results in similar ovulation rate to eCG but red blood cell indices may be affected

Background: The objective of this study was to investigate the metabolic and osmotic effects of different doses of
glycerol or a glycerol – propylene glycol mixture in Sarda sheep with the aim to identify those able to beneficially
modify ewe’s metabolic status without harmful changes in red blood cell (RBC) indices. Thereafter, the selected
doses were tested for their effects on ewe’s ovarian activity during an induced follicular phase and compared to
the effects of a hormonal treatment with equine chorionic gonadotrophin (eCG).
Results: Glycerol was administered alone (G groups: 90% glycerol and 10% water; % v/v) or in combination with
propylene glycol (M groups: 70% glycerol, 20% propylene glycol, 10% water; % v/v). Treatments were formulated to
provide 100, 75, 50 and 25% of the amount of energy supplied in previous experiments. Obtained results showed
that the formulations G75 and M75 (22.5 and 18.2% on DM basis, respectively) induce metabolic changes comparable
to those induced by M100. The latter dose has been already evaluated for its effects on sheep metabolism and
reproductive performance. However, with these high doses, plasma osmolality increased significantly, and RBC indices
showed significant alterations. The low dose groups (G25 and M25, 8.6 and 6.9% on DM basis, respectively) did not
show any alterations in plasma osmolality and RBC indices, but the metabolic milieu differed markedly from that of
M100. Between the medium dose groups, M50 (12.9% on DM basis) showed a more comparable milieu to M100 than
G50 (15.9% on DM basis) and no RBC alterations. Therefore, M75, G75 and M50 doses were tested for their effect on
ovarian functions and proved to be equally effective as eCG.
Conclusion: The results of the present study evidenced an alteration of RBC indices, and possibly of their functions, as
a side effect of glycerol administration at high doses in the diet of ewes. Therefore, protocols foreseeing the
administration of glycerol should be tested for their effects on RBC indices and functions. In general terms, the
medium dose of the glucogenic mixture (12.9% of dietary DM on offer) should be preferred.