Effect of substituting barley with glycerol as energy feed on feed intake, milk production and milk quality in dairy cows in mid or late lactation

The experiment reported in this research paper aimed to determine the level at which glycerol can substitute barley in grass-clover silage-based ration for dairy cows in mid or late lactation, without affecting milk production, milk composition, milk free fatty acid (FFA) profile, and milk sensory quality. Forty Holstein cows were used in a 4 x 4 Latin square experimental design. Crude glycerol substituted barley in the partially mixed ration (PMR) of the cows at inclusion levels of 0% (Gly0), 6% (Gly6), 12% (Gly12), and 18% (Gly18) of dietary dry matter (DM). Individual milk production, feed intake, and milking frequency were recorded daily, while milk composition and milk FA daily were analyzed weekly. Milk sensory analysis was performed on fresh and 7 d stored samples for the four diets. The PMR intake increased almost 1 kg from GlyO to Gly12, and decreased by approximately 1 kg from Gly12 to Gly18. Concentrate intake at the automated milking unit tended to decrease by half a kg from GlyO to Gly6. Milk yield decreased linearly with increasing proportions of glycerol in the diet while fat and protein contents in milk increased. This resulted in a quadratic effect of dietary glycerol level on ECM yield, with maximum yield with Gly6 and the lowest yield with Gly18. Protein and lactose yields decreased linearly with increasing proportions of glycerol in the diet. With increasing glycerol proportion in the diet, palmitic acid, oleic acid, linoleic acid, linolenic acid, and conjugated linoleic acid proportions in milk decreased linearly, while most of the short and medium chain FFA proportions in milk increased. To conclude, glycerol, as an energy feed, can substitute barley up to 18% of dietary DM for dairy cows in mid or late lactation without affecting milk quality. However, including more than 12% dietary glycerol might decrease ECM yield.