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This Article Full Text (PDF) All Versions of this Article: jas.2007-0325v1 86/11/3079    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wickersham, T. A. Articles by Gnad, D. P. Search for Related Content PubMed PubMed Citation Articles by Wickersham, T. A. Articles by Gnad, D. P.

Effect of rumen degradable intake protein supplementation on urea kinetics and microbial use of recycled urea in steers consuming low-quality forage

T. A. Wickersham^*, E. C. Titgemeyer^*, R. C. Cochran^*, E. E. Wickersham^* and D. P. Gnad

^* Department of Animal Sciences and Industry Department of Clinical Sciences, Kansas State University, Manhattan 66506-1600

etitgeme{at}ksu.edu

Abstract

We evaluated the effect of increasing amounts of rumen degradable intake protein (DIP) on urea kinetics in steers consuming prairie hay. Ruminally and duodenally fistulated steers (278 kg BW) were used in a 4 x 4 Latin square and provided ad libitum access to low-quality prairie hay (4.9% CP). The DIP was provided as casein dosed ruminally, once daily in amounts of 0, 59, 118, and 177 mg of N/kg BW daily. Periods were 13 d long with 7 d for adaptation and 6 d for collection. Steers were in metabolism crates for total collection of urine and feces. Jugular infusion of ¹⁵N¹⁵N-urea followed by determination of urinary enrichment of ¹⁵N¹⁵N-urea and ¹⁴N¹⁵N-urea was used to determine urea kinetics. Forage and N intake increased (linear, P < 0.001) with increasing DIP. Retention of N was negative (-2.7 g/d) for steers receiving no DIP and increased linearly (P < 0.001; 11.7, 23.0, and 35.2 g/d for 59, 118, and 177 mg of N/kg BW daily) with DIP. Urea synthesis was 19.9, 24.8, 42.9, and 50.9 g of urea-N/d for 0, 59, 118, and 177 mg of N/kg BW daily (linear, P = 0.004). Entry of urea into the gut was 98.9, 98.8, 98.6, and 95.9% of production for 0, 59, 118, and 177 mg of N/kg BW daily, respectively (quadratic, P = 0.003). The amount of urea-N entering the gastrointestinal tract was greatest for 177 mg of N/kg BW daily (48.6 g urea-N/d) and decreased (linear, P = 0.005) to 42.4, 24.5, and 19.8 g urea-N/d for 118, 59, and 0 mg of N/kg BW daily. Microbial incorporation of recycled urea-N increased linearly (P = 0.02) from 12.3 g N/d for 0 to 28.9 g N/d for 177 mg of N/kg BW daily. Provision of DIP produced the desired and previously observed increase in forage intake, while also increasing N retention. The large percentage of urea synthesis that was recycled to the gut (95.9% even when steers received the greatest amount of DIP) points to the remarkable ability of cattle to conserve N when fed a low-protein diet.

Key Words: cattle • protein • recycling • urea

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