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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy Science

First Advisor

David J. Schingoethe


Sixteen lactating Holstein cows were utilized in a 4x4 Latin square with 4 wk periods to evaluate the response to supplemental fat and niacin. Diets were control, control plus niacin (12 g/d), added fat, and added fat plus niacin. All total mixed diets (DM basis) contained 25% alfalfa hay, 25% corn silage, and 50% respective concentrate mixture. Supplemental fat diets contained extruded soybeans in place of soybean meal and portions of the corn and barley in the control diets. Total mixed diets contained (DM basis for control and supplemental fat): 2.6 and 5.5% ether extract, 17.7 and 16.7% CP, 33.4 and 32.1% NDF and 19.8 an 19.5% ADF. The first 2 wks of each period were for acclimation to diets with data collected the last 2 wks of each period. Dry matter intakes were similar (P>.99) for all diets (24.5, 24.7, 24.5, and 24.7 kg/d). Milk production increased (P<.05) with the addition of fat, but was unaffected (P>.70) by niacin (32.8, 32.2, 35.1, and 36.4 kg/d). Milk fat percentages were unaffected (P>.10) by fat or niacin additions to the diet. Milk protein percentages were lower (P<.01) with the supplemental fat diets, but were unaffected (P>.56) by ·niacin (3.02, 3.11, 2.96, and 2.91%). Lactose percentages were slightly higher (P<.08) for the supplemental fat diets (4.79, 4.79, 4.86, and 4.85%). Short and medium chain length fatty acids present in the milk decreased (P<.01) with added fat diets (short: 24.6, 24.8, 21.0, and 19.9%; medium: 39.6, 39.6, 30.9, and 30.2%). Long chain fatty acids increased (P<.01) with the addition of fat (31.9, 31.6, 42.9, and 45.2%); and were further increased (P<.01) with niacin addition and supplemental fat. The percentage of unsaturated fat increased (P<.01) with supplemental fat diets (29.7, 29.4, 35.1, and 36.5%); but were unaffected (P>.25) by the addition of niacin. Ruminal volatile fatty acids, pH, and ammonia were unaffected (P>.09) by fat or niacin supplementation. Serum urea, plasma glucose, and plasma amino acids were unaffected (P>.10) by supplemental fat or niacin. Concentration of amino acids in arterial and venous plasma were similar. The first limiting amino acid as calculated by percent extraction was lysine for control diets and methionine for supplemental fat diets. Supplementing the diet with an unsaturated fat source increased milk production and the proportion of unsaturated fatty acids in milk, while niacin supplementation had no influence on milk yield or composition.

Library of Congress Subject Headings

Dairy cattle -- Feeding and feeds
Oils and fats in animal nutrition
Milk yield


Includes bibliographical references (pages 49-56)



Number of Pages



South Dakota State University


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