Mammary lipogenic enzyme activity, trans fatty acids and conjugated linoleic acids are altered in lactating dairy cows fed a milk fat-depressing diet.
The objectives of the present study were to examine the effect of a milk fat-depressing (MFD) diet on: 1) the activity of mammary acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), 2) ACC mRNA relative abundance and 3) distributions of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA) in milk fat. Twelve lactating Holstein cows were used in a single reversal design. Two diets were fed: a control diet (60:40% forage/concentrate) and an MFD diet (25:70% forage/concentrate, supplemented with 5% soybean oil). The MFD diet decreased (P: < 0 0.001) milk fat by 43% and ACC and FAS activity by 61 and 44%, respectively. A reduced ACC mRNA relative abundance (P: < 0.001) corresponded with the lower ACC activity. The fatty acids synthesized de novo were decreased (P: < 0. 002), whereas tFA were increased from 1.9 to 15.6% due predominantly to a change in trans-10-18:1 isomer (P: < 0.001). With the MFD diet, the trans-7, cis-9 and trans-10, cis-12 CLA isomers were elevated (P: < 0.001), in contrast to the decrease in trans-11-18:1 (P: < 0. 001) and cis-9, trans-11-18:2. The data were consistent with a dietary effect on mammary de novo FA synthesis mediated through a reduction in ACC and FAS activity and in ACC mRNA abundance. The results were compatible with a role of trans-10, cis-12 CLA in milk fat depression, but alterations noted in tFA and other CLA isomers suggest that they also may be important during diet-induced milk fat depression.
Piperova
L S
LS
Department of Animal and Avian Sciences and. Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA.
Teter
B B
BB
Bruckental
I
I
Sampugna
J
J
Mills
S E
SE
Yurawecz
M P
MP
Fritsche
J
J
Ku
K
K
Erdman
R A
RA
D000103:Acetyl-CoA Carboxylase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet; D064429:Fatty Acid Synthases / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D005260:Female; D007774:Lactation; D008041:Linoleic Acids / Q000378:metabolism; D008055:Lipids / Q000032:analysis / Q000096:biosynthesis*; D008321:Mammary Glands, Animal / Q000201:enzymology*; D008892:Milk / Q000737:chemistry; D008894:Milk Proteins / Q000032:analysis / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis
D005227:Fatty Acids; D008041:Linoleic Acids; D008055:Lipids; D008894:Milk Proteins; D012333:RNA, Messenger; D064429:Fatty Acid Synthases; D000103:Acetyl-CoA Carboxylase