Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Dairy Science


Milk fatty acid composition can be modified to increase healthfulness through manipulations of the cow's diet. A series of experiments were conducted to increase concentrations of two specific fatty acids: transvaccenic acid and the cis-9, trans-11 isomer of conjugated linoleic acid. The consumption of this conjugated linoleic acid isomer has been linked to health benefits such as anticarcinogenesis and antiatherosclerosis. The mammalian body has enzymes capable of converting transvaccenic acid into the conjugated linoleic acid isomer, resulting in this dissertations focus on increasing it along with conjugated linoleic acid. Dietary fatty acid composition can influence milk fatty acid composition if the dietary lipid is protected from ruminal biohydrogenation. Oilseeds provide some protection from rurninal biohydrogenation. The first experiment in this dissertation fed high oil corn as an oilseed source to alter milk fatty acid composition. High oil corn was compared to conventional com in diets formulated with two dietary forage to concentrate ratios. Production parameters were influenced by forage concentration, but were not significantly influenced by corn source. Milk fatty acid composition, conversely was affected by corn source. but only minimally affected by forage concentration. However, increases in conjugated linoleic and transvaccenic acids were small. Marine products, including fish oil, have been shown to dramatically increase milk conjugated linoleic and transvaccenic acids, even though fish oil has low concentrations of fatty acids that are known precursors of these fatty acids. This observation led to the hypothesis that fish oil stimulates ruminal conversion of linoleic and linolenic acids present in other feedstuffs into conjugated linoleic and transvaccenic acids. Consumption of fish oil by dairy cattle, however, often leads to lower feed intake, milk production, and milk fat concentration. Experiments two and three investigated decreased amounts of fish oil fed in combination with extruded soybeans as a source of linoleic acid. These experiments indicate that the presence of fish oil increases conjugated linoleic and transvaccenic acids much more than extruded soybeans without fish oil, but that only small amounts of fish oil are required to cause this increase. Holsteins and Brown Swiss were used in both of these experiments and Holstein milk conjugated linoleic and transvaccenic acids was more responsive to dietary changes than was Brown Swiss milk, but Brown Swiss milk inherently contained more of these fatty acids. Plasma triglyceride fatty acid concentrations were measured in coccygeal artery and subcutaneous abdominal vein blood samples in the third experiment. Conjugated linoleic acid was present only in very small quantities, but transvaccenic acid was present in appreciable quantities for all diets and was responsive to dietary manipulation. This agrees with other research suggesting that most milk conjugated linoleic acid results by endogenous synthesis from transvaccenic acid. The current research shows that high levels of milk conjugated linoleic and transvaccenic acids can be achieved by feeding low amounts of fish oil with extruded soybeans.

Library of Congress Subject Headings

Milkfat Fatty acids in human nutrition Linoleic acid Dairy cattle -- Feeding and feeds Fish oils as feed Soybean as feed



Number of Pages



South Dakota State University