title: Combined effects of trans-10,cis-12 conjugated linoleic acid, propionate, and acetate on milk fat yield and composition in dairy cows.
abstract: Diets inducing milk fat depression (MFD) are known to alter ruminal lipid metabolism, leading to the formation of specific isomers [such as trans-10,cis-12 conjugated linoleic acid (CLA)] that inhibit milk fat synthesis in lactating dairy cows. However, ruminal outflow of these isomers does not fully account for the decreases in milk fat synthesis observed during diet-induced MFD. The high-concentrate diets inducing MFD also induce a greater production of propionate, suggesting a possible inhibition of milk fat by propionate associated with trans-10,cis-12-CLA during MFD. The present experiment aimed to study the combined effects of propionate and trans-10,cis-12-CLA (both inhibitors of milk fat synthesis) on milk fat secretion and the effects of the combination of 2 nutrients with opposite effects (acetate and propionate). Six Holstein cows were used in a 6×6 Latin square design with 21-d periods (14 d of nutrient infusion). The treatments were control; ruminal infusion of 1,500 g/d of acetate (A); ruminal infusion of 800 g/d of propionate (P); duodenal infusion of 1.60 g/d of trans-10,cis-12-CLA (CLA); ruminal infusion of 750 g/d of acetate+400 g/d of propionate (A+P); and duodenal infusion of 1.60 g/d of trans-10,cis-12-CLA+ruminal infusion of 800 g/d of propionate (CLA+P). The amounts of nutrients infused were chosen to induce a similar variation in milk fat content. Treatments A and P decreased dry matter intake. Compared with the control, P and CLA treatments decreased milk fat content and yield by 9% and 15% on average. Treatment A increased milk fat content by 6.5% but did not modify milk fat yield (because of a decrease in milk yield). The effects of A and P, and CLA and P on milk fat and fatty acid percentages and yield were additive (A+P and CLA+P treatments). With a same dose of trans-10,cis-12-CLA, the additional supply of propionate induced a decrease in milk fat 40% higher than that induced by trans-10,cis-12-CLA alone. The milk fatty acid profile obtained with CLA+P was similar to those observed with high-concentrate diets inducing MFD. In conclusion, under our experimental conditions, the effects of the 3 nutrients were additive on mammary lipogenesis, regardless of their separate effects. We also show that propionate could contribute to the milk fat reductions unaccounted for by trans-10,cis-12-CLA during MFD induced by high-concentrate diets.
authors.affiliation: INRA UMR 1080 Production du Lait, F-35590, Saint-Gilles, France.
authors.forename: G
authors.initials: G
authors.lastname: Maxin
authors.forename: F
authors.initials: F
authors.lastname: Glasser
authors.forename: C
authors.initials: C
authors.lastname: Hurtaud
authors.forename: J L
authors.initials: JL
authors.lastname: Peyraud
authors.forename: H
authors.initials: H
authors.lastname: Rulquin
mesh_terms: D000085:Acetates / Q000378:metabolism / Q000494:pharmacology*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D004041:Dietary Fats / Q000032:analysis*; D004386:Duodenum / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis; D005260:Female; D005503:Food Additives / Q000378:metabolism / Q000494:pharmacology*; D007774:Lactation / Q000187:drug effects / Q000378:metabolism; D044243:Linoleic Acids, Conjugated / Q000378:metabolism / Q000494:pharmacology*; D008892:Milk / Q000737:chemistry* / Q000187:drug effects; D011422:Propionates / Q000378:metabolism / Q000494:pharmacology*; D012417:Rumen / Q000378:metabolism
chemical_list: D000085:Acetates; D004041:Dietary Fats; D005227:Fatty Acids; D005503:Food Additives; D044243:Linoleic Acids, Conjugated; D011422:Propionates; C496197:trans-10,cis-12-conjugated linoleic acid