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Effects of crude glycerin supplementation on fatty acids composition of milk fat from primiparous lactating cows on irrigated tropical pasture
The objective of this study was to evaluate the effect of different levels of crude glycerin suplementation on fatty acids composition of milk fat from primiparous lactating cows grazing on irrigated tropical pasture. The experiment was conducted at Rancho Santana farm, located in Jequié city, Bahia, Brazil, in the period from December 21, 2010 to March 16, 2011. Ten ¾ Holstein × ¼ Dairy Gyr lactating primiparous cows, with 109±24 days of lactation and a mean age of 30±6 months and mean body weight of 426.2±68.29 kg were distributed into five treatments, using two simultaneous 5 × 5 latin squares. Treatments consisted of inclusion levels (0, 94, 191, 289, 389 g/kg dry matter basis) of crude glycerin (CG) in the supplement. Fatty acid methyl esters were analyzed by Thermo Finnigan Trace-GC-Ultra gas chromatography. Results were statistically analyzed by variance and regression analyses at 0.05 probablity. Results showed effects on milk fat saturated fatty acids - caproic (6:0), caprylic (8:0), capric (10:0), lauric (12:0), pentadecanoic (15:0) and stearic (18:0) - when the crude protein concentrations in supplement increased. The increase of CG level in the supplement did not differ the polyunsaturated fatty acids (P<0.05). To determine the ratio between pro- and anti-atherogenic acids, the atherogenic index (IA) and thrombogenic index (IT) were calculated, and difference was verified only for IA (P<0.05). Treatments affected a few of the saturated and monounsaturated fatty acids. Overall, this data indicated that the addition of glycerin did not cause effects on the variables that express the milk quality, so the recommended crude glycerin level could be increased to 389 g (171 g glycerol) per kg of supplement.
Keywords: glycerol, biohydrogenation, biodiesel