Abstract
BackgroundThe 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).ResultsGlycerol 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.ConclusionThe 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.
Highlights
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
Phase 1 Body weight did not change after the administration of the dietary treatments and no differences were observed between groups (M100 51.6 ± 1.7, G100 53.8 ± 3, M75 51.6 ± 2.1, G75 50.3 ± 1.8, M50 48.7 ± 1.9, G50 48.1 ± 1.8, M25 50.1 ± 1.8, G25 50.6 ± 3.8; P > 0.05)
Before starting the titration feeding treatments, plasma osmolality, RBC indices, circulating concentrations of analysed metabolites and hormones were within the physiological ranges for the species [38] in all the ewes showing no differences between groups (D 0; Table 1)
Summary
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. Other studies in ewes reported an increase in insulin [19,20,21], insulin-like growth factor-1 [20], and a decrease in urea circulating concentrations [20, 21] after oral administration of 280 mL glycerol and 80 mL 1,2- propylene glycol daily for 4 days These changes have been associated with changes in follicular fluid composition during treatment period [20], and may contribute in creating a suitable systemic and local metabolic milieu for the promotion of ovarian function. Thanks to its boosting activity on ovarian functions, glycerol could possibly substitute for synthetic gonadotropins dosed to increase lambing and twinning rates in sheep Among them, it is noteworthy the equine chorionic gonadotropin (eCG), a hormone commonly used in concert with progestogen to induce ovulation prior to natural mating or artificial insemination. There is a need for alternative synchronization protocols without eCG [25]
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