Submitted to: Conference Proceedings of Canadian Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: April 18, 2003
Publication Date: June 10, 2003
Citation: SWANSON, K., FREETLY, H.C., FERRELL, C.L. UREA NITROGEN RECYCLING AND NITROGEN BALANCE IN LAMBS FED LOW-QUALITY HAY AND INFUSED WITH DIFFERING PROPORTIONS OF CASEIN IN THE RUMEN AND ABOMASUM. CONFERENCE PROCEEDINGS OF CANADIAN SOCIETY OF ANIMAL SCIENCE, PAGE 34, SASKATOON, SASKATCHEWAN, CANADA. 2003. Technical Abstract: Twenty wether lambs (46 ± 2 kg) fitted with ruminal and abomasal infusion catheters were used in a completely randomized design to determine the effects of differing proportions of ruminal and abomasal casein infusion on urea N recycling and N balance in lambs fed low-quality brome hay (0.8% N, DM basis) for ad libitum intake. Wethers were infused with 0 (control) or 10.7 g/d of N from casein with ratios of ruminal:abomasal infusion of 100:0 (100R:0A), 67:33 (67R:33A), 33:67 (33R:67A), or 0:100% (0R:100A), respectively, over a 12-d period. Total N supply (g/d) was greater (P < 0.10) in lambs receiving casein infusion (mean = 15.3) as compared to controls (3.9). Urinary N excretion (g/d) was greatest (P < 0.10) in lambs receiving 100R:0A (10.9), least for control (2.1), with 67R:33A (8.7), 33R:67A (8.0), 0R:100A (8.2) intermediate. Retained N (g/d) was greatest (P < 0.10) in lambs receiving 67R:33A (2.4), 33R:67A (2.9), and 0R:100A (2.8), least for control (-1.8), with 100R:0A (0.0) intermediate. Urinary urea N excretion (g/d) was greatest (P < 0.10) in lambs receiving 100R:0A (9.7), least for control (0.6), with 67R:33A (7.1), 33R:67A (7.2), and 0R:100A (7.7) intermediate. Urea N production (g/d) was greatest (P < 0.10) in lambs receiving 100R:0A (22.5), least for control (3.7), with 67R:33A (17.1), 33R:67A (20.1), and 0R:100A (21.1) intermediate. Urea N entry to the gastrointestinal tract (g/d) was greater (P < 0.10) in lambs receiving casein (mean = 12.3) than controls (3.1), but did not differ between casein infusion treatments. Apparent N, DM, and energy digestibility (% of intake) was greater (P < 0.10) in lambs infused with casein than controls. These data suggest that feeding protein supplements containing over approximately 33% of the crude protein as ruminally undegradable intake protein, as compared to 100% ruminally degradable intake protein, to lambs consuming low-quality forage increases N retention and the efficiency of N utilization. This likely occurs through increased utilization of feed N for body protein synthesis and not increased urea N recycling to the gastrointestinal tract.