title: 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.
abstract: 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 (17.5 g/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 <16, increased the proportion of total C18, increased the proportion and yield of trans-10 C18:1, and increased the proportion of trans-10,cis-12 conjugated linoleic acid in milk fatty acids (FA). As dietary C18:1 or C18:2 increased beyond the concentration present in LOLL, milk fat concentration, milk fat yield, and proportion and yield of milk C <16 all decreased, and the proportion and yield of milk trans-10 C18:1 increased. A quadratic effect on milk fat concentration and yield was noticed for C18:2 feeding, but not for C18:1 feeding. When dietary contents of total FA and FA other than C18:1 and C18:2 were similar, C18:2-rich diets decreased milk fat concentration and yield compared with C18:1-rich diets (LOML vs. MOLL, and LOHL vs. HOLL), indicating that C18:2 is more potent than C18:1 for depressing milk fat. Increasing dietary FA content from no fat to LOLL, which increased primarily C18:1 and C18:2 with small increases in C18:0 and C16:0, decreased the secretion of C <16 but increased total C18 secretion in milk. This suggests that biohydrogenation intermediates act to decrease mammary FA synthesis at low levels of added C18:1 and C18:2. No significant monensin × fat interactions were detected for the milk composition parameters analyzed; however, a monensin × fat interaction was found for milk fat trans-10 C18:1 proportion.
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706, USA. learment@facstaff.wisc.edu
authors.forename: M
authors.initials: M
authors.lastname: He
authors.forename: K L
authors.initials: KL
authors.lastname: Perfield
authors.forename: H B
authors.initials: HB
authors.lastname: Green
authors.forename: L E
authors.initials: LE
authors.lastname: Armentano
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D000981:Antiprotozoal Agents / Q000494:pharmacology*; D002417:Cattle; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D005223:Fats / Q000032:analysis*; D005227:Fatty Acids / Q000032:analysis*; D005260:Female; D007774:Lactation / Q000187:drug effects*; D019787:Linoleic Acid / Q000494:pharmacology*; D008892:Milk / Q000737:chemistry / Q000378:metabolism*; D008985:Monensin / Q000494:pharmacology*; D019301:Oleic Acid / Q000494:pharmacology*
chemical_list: D000981:Antiprotozoal Agents; D005223:Fats; D005227:Fatty Acids; D019301:Oleic Acid; D008985:Monensin; D019787:Linoleic Acid