The effect of dietary glycerol supplementation on milk production and composition, blood parameters and performance of lactating sows

Modern lactating sows have an increased demand for nutrients for the large litter size compared to the traditional genotypes. Glycerol is considered to be a good alternative to moderate the energy deficiency and provide energy supply in the feed of lactating sow. The aim of our study was to evaluate the effect of a liquid "feed grade" glycerol source on the milk production and milk composition of sows including its fatty acid profile, on the major physiological indicators of sows, and on the digestibility of nutrients. The trial was conducted with Danish LandracexDanish Yorkshire (323 +/- 17.0 kg) sows (n = 12/treatment) and their litters. 5% glycerol supplementation increased the milk yield on d 21 of lactation [control (C): 8.94 +/- 2.27 kg/d vs. 5% glycerol (G): 10.39 +/- 1.56 kg/d; P<0.05], but had no effect on the milk production of the total lactation period (P>0.05). Glycerol inclusion decreased the milk protein content on d 14 and d 21 and had a decreasing effect on the milk protein (CP) content in the total lactation period, either (C: 5.33 +/- 0.40 g/100 g milk vs. G: 5.15. +/- 0.33 g/100 g milk; P<0.05). Glycerol supplementation did not influence the dry matter (DM), ether extract (EE) and lactose content. 5% glycerol did not have any effect on the feed intake, live weight, back-fat thickness, and weaning-to-oestrus interval of lactating sows and neither did significantly influence the weaning weight of the piglets. There was no difference between control and experimental groups in total protein, albumin and triglyceride concentration of blood samples of sows and in the activity of liver enzymes (ALT, AST, GGT), but there was a tendency (P<0.10) for increased plasma glucose (C: 4.94 +/- 0.29 mmol/L vs. G: 5.17 +/- 0.55 mmol/L) and cholesterol (C: 2.10 +/- 0.27 mmol/L vs. G: 2.34 +/- 0.33 mmol/L) in the experimental group. Due to the 5% glycerol supplementation, the ratio of total saturated fatty acids (SFAs) of the milk fat decreased (C: 43.47 +/- 3.37 g/100 g fatty acid vs. G: 39.39 +/- 4.51 g/100 g fatty acid; P<0.05). In the SFAs group the ratio of C14:0 and C16:0 fatty acids decreased significantly compared with the control group (P<0.05). In contrast, there was a tendency for increased total monounsaturated fatty acids (MUFAs) content of the milk (C: 43.62 +/- 2.54 g/100 g fatty acid vs. G: 47.11 +/- 4.29 g/100 g fatty acid; P<0.10) but the total polyunsaturated fatty acids (PUFAs) content was not affected (C: 12.88 +/- 1.23 g/100 g fatty acid vs. G: 13.50 +/- 0.64 g/100 g fatty acid;). The total n-3 PUFAs proportion in the milk increased (C: 0.63 +/- 0.06 vs. G: 0.68 +/- 0.05; P<0.05). No differences were observed in the apparent total tract digestibility of DM, CP, EE and crude fiber between control and experimental groups. Our findings have shown that 5% "feed grade" glycerol can be fed with lactating sows without having a negative effect on the performance. Additional dose trials are needed to be performed in order to further study the effect of glycerol supplementation on milk production and on metabolic processes of lactating sows.