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Title: NITROGEN BALANCE IN LAMBS FED LOW-QUALITY BROME HAY AND INFUSED WITH DIFFERING PROPORTIONS OF CASEIN IN THE RUMEN AND ABOMASUM

Author
item Swanson, Kendall
item Freetly, Harvey
item Ferrell, Calvin

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2003
Publication Date: 2/1/2004
Citation: SWANSON, K., FREETLY, H.C., FERRELL, C.L. NITROGEN BALANCE IN LAMBS FED LOW-QUALITY BROME HAY AND INFUSED WITH DIFFERING PROPORTIONS OF CASEIN IN THE RUMEN AND ABOMASUM. JOURNAL OF ANIMAL SCIENCE. 2004. V. 82. P. 502-507.

Interpretive Summary: The nutrient value of grazed forages for cattle and sheep typically decreases when the forage becomes mature. This drop in nutritive value can result in cattle and sheep losing weight and body nitrogen when these forages are their sole source of food. This drop in feed quality is partially the result of nitrogen (or protein) content becoming too low to allow cattle and sheep to effectively digest the forage. This study found that providing additional nitrogen to animals eating forage low in nitrogen improved the animals' ability to return nitrogen previously absorbed from food to the digestive tract. Improving nitrogen recycling decreased the rate at which animals were losing body nitrogen. This study also found that providing some of the nitrogen post-ruminally as a high quality protein resulted in additional increases in the nitrogen retained by the animal.

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 (hay N intake + N from casein infusion) was greater (P < 0.10) in lambs receiving casein infusion as compared to controls. Urinary N excretion (g/d) was greatest (P < 0.10) in lambs receiving 100R:0A, least for control, with 67R:33A, 33R:67A, 0R:100A intermediate. Apparently digested N (g/d and % of N intake) was greater (P < 0.10) in lambs infused with casein than controls, but did not differ between casein infusion treatments. Retained N (g/d) was greatest (P < 0.10) in lambs receiving 67R:33A, 33R:67A, and 0R:100A, least for control, with 100R:0A intermediate. Urinary urea N elimination was greatest (P < 0.10) in lambs receiving 100R:0A, least for control, with 67R:33A, 33R:67A, and 0R:100A intermediate. Urinary urea N production was greatest (P < 0.10) in lambs receiving 100R:0A, least for control, with 67R:33A, 33R:67A, and 0R:100A intermediate. Urinary urea N entry to the GIT was greater (P < 0.10) in lambs receiving casein than controls, but did not differ between casein infusion treatments. Apparent DM, OM, and energy digestibility (% of intake) was greater (P < 0.10) in lambs infused with casein than controls, but did not differ between casein infusion groups. 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.