Evaluation of milk somatic cells as a source of mRNA for study of lipogenesis in the mammary gland of lactating beef cows supplemented with dietary high-linoleate safflower seeds.
Our objectives were 2-fold: to determine the effect of dietary linoleate on milk fat composition and on transcript abundance of acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), lipoprotein lipase (LPL), and stearoyl-CoA desaturase (SCD) mRNA in mammary tissue, and to evaluate milk somatic cell mRNA as a source of mammary tissue mRNA for these enzymes. Eighteen primiparous, crossbred beef cows (BW = 411 +/- 24 kg; BCS = 5.25) were offered Foxtail millet hay at 1.68% of BW daily and either a low-fat control (n = 9) or a high-linoleate (79% 18:2n-6), cracked safflower seed supplement (n = 9). Diets were isonitrogenous and isocaloric, and the linoleate diet contained 5.4% of DMI as fat. At slaughter (37 +/- 3 d postpartum), mammary tissue was sampled and immediately frozen in liquid N2 before being stored at -80 degrees C. Milk samples were obtained from the same mammary glands and immediately centrifuged at 1,200 x g to pellet somatic cells. A ribonuclease protection assay was used to quantify the mRNA in the mammary gland and milk somatic cells. Effects of diet, tissue, or their interaction were not observed for ACC (P = 0.28, 0.89, and 0.35, respectively), FAS (P = 0.38, 0.66, and 0.20, respectively), LPL (P = 0.09, 0.15, and 0.43, respectively), or SCD (P = 0.45, 0.19, and 0.29, respectively). Dietary effects on fatty acid profile of the milk fat suggested that linoleate supplementation might have decreased de novo lipogenesis while increasing uptake of dietary fatty acids; this effect was consistent with a trend toward greater LPL mRNA for linoleate-fed cows (P = 0.09). Correlations (r values) between mammary tissue and milk somatic cell data for each mRNA for the low-fat control diet were: ACC, 0.76 (P = 0.02); FAS, 0.69 (P = 0.04); LPL, 0.68 (P = 0.04); and SCD, 0.73 (P = 0.05), and for the linoleate diet were: ACC, 0.85 (P = 0.003); FAS, 0.75 (P = 0.02); LPL, 0.90 (P = 0.001); and SCD, 0.73 (P = 0.03). We conclude that milk somatic cells obtained from lactating beef cows can be used as a source of RNA to study nutritional regulation of mammary gland lipogenesis in cows fed dietary fat supplements.
Murrieta
C M
CM
Department of Animal Science, University of Wyoming, Laramie, Wyoming 82071, USA.
Hess
B W
BW
Scholljegerdes
E J
EJ
Engle
T E
TE
Hossner
K L
KL
Moss
G E
GE
Rule
D C
DC
D000103:Acetyl-CoA Carboxylase / Q000235:genetics / Q000378:metabolism; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D031187:Carthamus tinctorius / Q000378:metabolism*; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D064429:Fatty Acid Synthases / Q000235:genetics / Q000378:metabolism; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D007774:Lactation / Q000502:physiology*; D019787:Linoleic Acid / Q000737:chemistry / Q000378:metabolism; D050155:Lipogenesis; D008071:Lipoprotein Lipase / Q000235:genetics / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism*; D008892:Milk / Q000166:cytology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds; D013230:Stearoyl-CoA Desaturase / Q000235:genetics / Q000378:metabolism
D012333:RNA, Messenger; D019787:Linoleic Acid; D013230:Stearoyl-CoA Desaturase; D064429:Fatty Acid Synthases; D008071:Lipoprotein Lipase; D000103:Acetyl-CoA Carboxylase