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

Abstract

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.

Towards a Sustainable Reproduction Management of Dairy Sheep: Glycerol-Based Formulations as Alternative to eCG in Milked Ewes Mated at the End of Anoestrus Period

“…Research efforts are focusing on finding alternative treatments to eCG administration in protocols to induce oestrus and ovulation in small ruminants [ 4 , 27 , 28 ] considering the concerns linked to its production for brood mare health and welfare [ 29 ]. The reduction in the use of synthetic hormones in livestock farming would also meet consumer demand for “natural, green, and clean” methods [ 30 ].…”

“…Insulin concentration was measured in duplicate using a commercial ovine insulin ELISA Kit (Mercodia developing diagnostics, Marburg, Germany) which is a solid-phase ELISA based on the direct sandwich technique. The kit is calibrated against an in-house reference preparation of ovine insulin, and it has been previously used for insulin determination in ovine plasma [ 3 , 4 ]. The mean ovine insulin concentrations of the six reference solutions were 0, 0.05, 0.15, 0.5, 1.5, and 3 mg/L.…”

“…We have recently reported that the administration of glucogenic glycerol-based formulation to Sarda ewes was able to elicit an ovulatory response which did not differ from that of eCG-treated ewes dosed with water [ 4 ]. However, the study was conducted during the natural breeding season using a PGF-based synchronization protocol without the administration of progesterone.…”

“…However, a previous study showed that the short-term administration of a high dose of glucogenic mixture (23% on dry matter intake basis) to milked ewes resulted in a temporary reduction of milk yield and milk lactose content and an increase of milk protein and casein. Therefore, considering both these changes in milk yield and composition and the recently reported potential side effects of glycerol on red blood cell indices and plasma osmolality [ 4 ], the dose given should be carefully set. In a previous study we reported that medium doses of glucogenic mixtures (≈12% on dry matter intake basis) should be preferred for flushing dairy ewes, as they proved to be effective at metabolic level without causing alterations in RBC indices or possibly in their functionality [ 4 ].…”

“…The present study arose from this finding. Keeping in mind the above premises, it was aimed at (1) investigating whether the administration of eCG in a standard synchronization protocol could be replaced by the administration of glycerol-based formulations in milked ewes at the end of their seasonal anoestrus; (2) monitoring the changes in lipid profile, liver and kidney function consequent to glycerol administration; (3) assessing whether the dose set in a previous study; and [ 4 ] preserving milk yield and composition. Moreover, given the high diffusibility of glycerol across plasma membranes, the concentrations of milk glycerol were also determined.…”