Effects of feeding whole-cracked rapeseeds, nitrate, and 3-nitrooxypropanol on composition and functional properties of the milk fat fraction from Danish Holstein cows.

An 8 × 8 incomplete Latin square design was conducted with 48 lactating Danish Holstein cows over 6 periods of 21 days each. Eight diets were 2 × 2 × 2 factorially arranged: FAT (30 or 63 g crude fat/kg DM), NITRATE (0 or 10 g nitrate/kg DM), and 3-NOP (0 or 80 mg 3-NOP/kg DM), and cows were fed ad libitum. Milk samples were analyzed for general composition, fatty acids (FA) and thermal properties of milk fat.

Milk fat content was decreased by supplementing fat but increased by 3-NOP. The changes in FA composition were mainly driven by the FAT × 3-NOP interaction. Fat supplementation shifted milk FA composition toward a lower content of SFA and greater contents of MUFA and PUFA, whereas these effects became smaller in combination with 3-NOP. However, 3-NOP had no effects on SFA, MUFA, or PUFA in low-fat diets. Fat supplementation lowered the solid-fat content in milk fat because of the decreased SFA content. The onset crystallization temperature of milk fat was decreased by 3-NOP when supplemented in low-fat diets. As a result of the FAT × 3-NOP interaction, supplementation of fat without 3-NOP shifted the peak temperature of the low-melting fraction of milk fat toward low temperature because of a decreased proportion of C16:0 and increased the proportions of C18:1 cis-9, C18:1 trans-11, C18:2 cis-9, and CLA cis-9 trans-11 fatty acids.

In conclusion, no additive effects were observed among FAT, NITRATE, and 3-NOP on chemical and thermal properties of milk fat, and fat supplementation largely changed milk FA composition, which in turn affected the thermal properties of milk fat. These effects should be borne in mind when fat and these additives are supplemented for the purpose of decreasing methanogenesis in the rumen.