title: Effect of dietary crude protein concentration on ruminal nitrogen metabolism in lactating dairy cows.
abstract: Ten lactating Holstein cows fitted with ruminal cannulas that were part of a larger feeding trial were blocked by days in milk into 2 groups and then randomly assigned to 1 of 2 incomplete 5 x 5 Latin squares. Diets contained [dry matter (DM) basis] 25% alfalfa silage, 25% corn silage, and 50% concentrate. Rolled high-moisture shelled corn was replaced with solvent-extracted soybean meal to increase crude protein (CP) from 13.5% to 15.0, 16.5, 17.9, and 19.4% of DM. Each of the 4 experimental periods lasted 28 d with data and sample collection performed during the last 8 d. Digesta samples were collected from the omasum to quantify the ruminal outflow of different N fractions. Intake of DM was not affected but showed a quadratic trend with maxima of 23.9 kg/d at 16.5% CP. Ruminal outflow of total bacterial nonammonia N (NAN) was not different among diets but a significant linear effect of dietary CP was detected for this variable. Bacterial efficiency (g of total bacterial NAN flow/kg of organic matter truly digested in the rumen) and omasal flows of dietary NAN and total NAN also showed positive linear responses to dietary CP. Total NAN flow increased from 574 g/d at 13.5% CP to 688 g/d at 16.5% CP but did not increase further with the feeding of more CP. Under the conditions of this study, 16.5% of dietary CP appeared to be sufficient for maximal ruminal outflow of total bacterial NAN and total NAN.
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
authors.forename: J J Olmos
authors.initials: JJ
authors.lastname: Colmenero
authors.forename: G A
authors.initials: GA
authors.lastname: Broderick
mesh_terms: D000818:Animals; D001419:Bacteria / Q000378:metabolism; D002417:Cattle / Q000378:metabolism*; D004032:Diet; D004043:Dietary Fiber / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage*; D004063:Digestion; D005260:Female; D007774:Lactation; D000455:Medicago sativa; D009584:Nitrogen / Q000378:metabolism*; D009851:Omasum / Q000378:metabolism; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology; D012820:Silage; D030262:Soybean Proteins; D003313:Zea mays
chemical_list: D004043:Dietary Fiber; D004044:Dietary Proteins; D030262:Soybean Proteins; D009584:Nitrogen