| Two studies were conducted to identify the effect of fat supplementation with different fatty acid profiles on milk fat depression in dairy cattle. Twenty four cows in the first experiment were blocked by milk production and antioxidant (AGRADO plus) feeding as main-plot and fed one of the 6 oil diets in 6x6 Latin Square as sub-plot. The 6 oil treatments were no added oil (CTRL), or 5% DM oil from palm (PALM), high-oleic safflower (OSAF), high-linoleic safflower (LSAF), linseed (LNSD) or corn (CORN). Milk fat yield and fatty acid composition were not affected by AGRADO plus supplementation. Compared to CTRL, milk fat yield and concentration were effectively maintained by PALM, whereas other oils decreased milk fat concentration, and milk short-chain fatty acids concentration and yield. Feeding C18:2-rich oils CORN or LSAF caused significant milk fat depression compared to CTRL. Potencies of C18:1 and C18:3 on milk fat yield appear to be equal. In the second experiment, 56 cows were used in a split-plot design with parityxmonensin feeding as main-plot and fed one of the 7 fat blend diets in 7x7 Latin Square as sub-plot. Seven fat blend treatments were no added fat (NoFAT), or feeding increasing levels of C18:1 or C18:2: low C18:1 + low C18:2 (LOLL); low C18:1 + medium C18:2 (LOML); low C18:1 + high C18:2 (LOHL); medium C18:1 + low C18:2 (MOLL); medium C18:1 + medium C18:2 (MOML); high C18:1 + low C18:2 (HOLL). Feeding monensin decreased proportion of C<16 and increased proportions of trans-10 C18:1 and trans-10, cis-12 CLA in milk FA, which indicated altered rumen biohydrogenation. As either C18: I or C18:2 increased beyond that in LOLL, milk fat concentration and yield, C<16 and C16:0 proportions and yields decreased linearly, and trans-10 C18:1 proportion and yield increased linearly. Quadratic effects on milk fat concentration and yield were only observed for C18:2 feeding. Increasing dietary Fatty acid concentration from NoFAT to LOLL reduced synthesis of C<16. This suggests reduced mammary fatty acid synthesis occurs at low levels of added C18:1 and C18:2. Monensinxfat interaction effect was only detected on milk fat trans-10 C 18:1 proportion. |
