Effects of Fat Saturation and Source of Fiber on
of Nutrient Digestion and Milk Production
by Lactating Dairy Cowsl92
J. PANTOJA, J. L. FIRKINS,, M. L.
were assigned to six treatments in a
Latin square design to evaluate the
effects of degree of fat saturation and
amount and source of effective fiber on
digestion and milk
production. Cows were fed for ad libi-
tum intake a control diet with no added
fat or diets with
added fat from
vegetable fat; the diets with animal-
vegetable fat had 40% forage,
Ruminal acetate:propionate was higher
when soyhulls replaced forage NDF be-
cause of the higher digestibility of soy-
hulls in the rumen and total tract. Rumi-
nal digestion of NDF was decreased as
unsaturation of fat increased. True and
apparent efficiencies of bacterial protein
synthesis were increased as fat unsatura-
reduced recycling of microbial
rumen. The digestibility of fatty acids in
the small intestine was higher in cows
fed no fat than in those fed fat and was
fat unsaturation decreased,
primarily because of the saturated tallow.
Dry matter intake was decreased
increased fat unsaturation.
ments depressed milk protein percentage.
Received October 29, 1993.
Accepted February 25, 1994.
'Salaries and research support provided by state and
federal funds appropriated to the Ohio Agncultd Re-
search and Development Center, The
sity. Contributing to Regional Research Project NC-185.
Article Number 221-93.
2Supported in part by the Ohio
tion Milk Check-Off
3Reprint quests: Plumb Hall, 2027 Coffey Road.
4Department of Veterinary Clinical Sciences.
B. L. HULL4
FCM tended to de-
crease linearly as unsaturation of fat in-
creased. In diets with
degree of saturation between saturated
tallow and tallow (iodine values of
appears to be optimum for fatty
acid digestibility and DMI.
fat saturation, effective fi-
ber, fatty acid digestibility, milk produc-
Abbreviation key: AVF
NH3 nonbacterial N,
High producing dairy cows require high
energy diets for maximal milk production in
early and midlactation and to replenish body
stores in mid to late lactation. The inclusion of
fats in diets to increase energy density has
became a common practice. Fats have the
potential to improve the efficiency of energy
utilization by converting preformed fatty acids
to milk fat without the heat loss as-
sociated with the conversion of carbohydrates