Effect of frequency and amount of rumen-degradable intake protein supplementation on urea kinetics and microbial use of recycled urea in steers consuming low-quality forage.
We evaluated the effect of frequency and amount of rumen-degradable intake protein (DIP) on urea kinetics in steers consuming prairie hay. Five ruminally and duodenally fistulated steers (366 kg of BW) were used in a 5 x 5 Latin square and provided ad libitum access to low-quality prairie hay (4.7% CP). Casein was provided daily in amounts of 61 and 183 mg of N/kg of BW (61/d and 183/d) and every third day in amounts of 61, 183, and 549 mg of N/kg of BW per supplementation event (61/3d, 183/3d, and 549/3d). Periods were 18-d long with 9 d for adaptation and 9 d for collection. Steers were in metabolism crates for total collection of urine and feces. Jugular infusion of (15)N(15)N-urea followed by determination of urinary enrichment of (15)N(15)N-urea and (14)N(15)N-urea was used to determine urea kinetics. Treatment means were separated to evaluate the effects of increasing DIP supplementation and the effects of frequency at the low (61/d vs. 183/3d) and at the high (183/d vs. 549/3d) amounts of DIP provision. Forage OM and total digestible OM intakes were linearly (P < or = 0.05) increased by increasing DIP provision but were not affected by frequency of supplementation at either the low or high amounts. Production and gut entry of urea linearly (P < or = 0.006) increased with DIP provision and tended to be greater (P < or = 0.07) for 549/3d than 183/d but were not different between 61/d and 183/3d. Microbial N flow to the duodenum was linearly (P < 0.001) increased by increasing DIP provision. Additionally, 183/d resulted in greater (P = 0.05) microbial N flow than 549/3d. Incorporation of recycled urea-N into microbial N linearly (P = 0.04) increased with increasing DIP. Microbial incorporation of recycled urea-N was greater for 549/3d than 183/d, with 42 and 23% of microbial N coming from recycled urea-N, respectively. In contrast, there was no difference due to frequency in the incorporation of recycled urea-N by ruminal microbes at the low level of supplementation (i.e., 61/d vs. 183/3d). This study demonstrates that urea recycling plays a substantial role in the N supply to the rumen and to the animal, particularly in steers supplemented infrequently with high levels of protein.
Wickersham
T A
TA
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600, USA.
Titgemeyer
E C
EC
Cochran
R C
RC
Wickersham
E E
EE
Moore
E S
ES
D000641:Ammonia / Q000378:metabolism / Q000652:urine; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001806:Blood Urea Nitrogen; D002417:Cattle / Q000378:metabolism*; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism*; D019587:Dietary Supplements; D004063:Digestion / Q000502:physiology; D004386:Duodenum / Q000378:metabolism / Q000382:microbiology; D004435:Eating / Q000502:physiology; D005285:Fermentation / Q000502:physiology; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology; D013997:Time Factors; D014508:Urea / Q000378:metabolism* / Q000652:urine
D004044:Dietary Proteins; D000641:Ammonia; D014508:Urea; D009584:Nitrogen