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Supplementation of Diets with Positive and Negative Urea Fermentation Potential Using Urea or Soybean Meal¹

University of Kentucky³, Lexington 40506

Abstract

Three experiments were conducted with lactating dairy cows to evaluate responses to addition of urea or soybean meal to basal diets containing inadequate concentrations of protein and either positive (Exp. 1) or negative (Exp. 2 and 3) urea fermentation potentials (UFP). In Exp. 1, a basal diet with 8.6% crude protein (UFP = +5.2) was increased to 16.5 to 17% crude protein with urea or soybean meal and fed to intact and rumen fistulated mature Holstein cows. Addition of either supplement significantly increased milk production and diet digestibility (dry matter, protein and acid detergent fiber). Soybean meal also increased intake. Urea resulted in the greatest amount of urinary N and soybean meal the greatest N retention. Intact and fistulated Holstein cows except only first lactation animals were used in Exp. 2. The basal diet contained 11.6% crude protein (UFP = –1.14), and 15.2% after the addition of either urea or soybean meal. Intake and digestion of dry matter and protein were significantly increased by increasing protein content, regardless of N source used. Digestion of acid detergent fiber was improved slightly. Milk production was not affected by treatment. A basal diet (13.6% crude protein, UFP = –1.71) supplemented to 17% with urea or soybean meal was used in Exp. 3. Holstein cows were blocked by age (18 first lactation, 15 older) and calving date. Treatments had no effect on intake or production of first lactation cows. Older cows responded to both urea and soybean meal supplements with slightly increased intake and a significant increase in fat and protein corrected milk. Corrected UFP values are cited.

¹ Published with the approval of the Director as Paper No. 78-5-66 Journal Series, Kentucky Agr. Exp. Sta.

² Present address: Animal Science Dept., Univ. of Nebraska, Lincoln 68583.

³ Animal Sciences Dept.

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