Effect of dietary fat blend enriched in oleic or linoleic acid and monensin supplementation on dairy cattle performance, milk fatty acid profiles, and milk fat depression

The effect of feeding increasing levels of oleic and linoleic acid both independently and together, with or without monensin, on milk fat depression was evaluated. Fifty-six Holstein cows were blocked by parity and then were divided by milk production into 2 groups (high or low) of 14 cows each within each parity block. A cow pair of 1 high and 1 low production cow within each parity block was fed in a single electronic feeding gate. Gates (n=28) were considered the experimental unit and were assigned to monensin (17.5g/t of dry matter) or control as the main plot (n=14 each). The 7 cow pairs in each of the fixed effect groups were further assigned to a sequence of fat blend diets as split plot. Seven fat blend treatments in the split plot 7×7 Latin square were no added fat (no fat) and diets with increasing levels of oleic or linoleic acid: 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); and high C18:1+low C18:2 (HOLL). Monensin feeding did not affect milk yield or concentration and yield of milk fat. Feeding monensin decreased the proportion of C