title: First results on the incorporation and excretion of 15N from orally administered urea in lactating pony mares.
abstract: Two lactating pony mares were given oral offers of 20 g 15N urea [95 atom-% 15N-excess (15N')] on 6 subsequent days. About 80% of the consumed 15N' were excreted via urine and faeces, but only about 2% via milk. The 15N' secreted via milk-lysine only amounted to 0.04% of the 15N' intake. The recovery was about 90% in each case. Tissues with active metabolism had an unexpectedly high labelling (greater than 0.3 atom-% 15N'). The low extent of the conversion of oral urea N into milk-lysine speaks against an essential participation of the enteral synthesis in meeting the amino acid requirement of lactating mares. It was already concluded from this results that the determination of the amino acid requirement will be necessary for this group of performance.
authors.affiliation: Faculty of Agricultural Sciences, Karl-Marx-University Leipzig, Department of Animal Nutrition Chemistry, Jena.
authors.forename: R
authors.initials: R
authors.lastname: Schubert
authors.forename: R
authors.initials: R
authors.lastname: Zander
authors.forename: K
authors.initials: K
authors.lastname: Gruhn
authors.forename: A
authors.initials: A
authors.lastname: Hennig
mesh_terms: D000284:Administration, Oral; D000596:Amino Acids / Q000378:metabolism; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D005243:Feces / Q000737:chemistry; D005260:Female; D006736:Horses / Q000378:metabolism*; D007774:Lactation / Q000378:metabolism*; D008892:Milk / Q000737:chemistry; D009584:Nitrogen / Q000097:blood / Q000378:metabolism* / Q000652:urine; D009587:Nitrogen Isotopes; D014508:Urea / Q000008:administration & dosage / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D009587:Nitrogen Isotopes; D014508:Urea; D009584:Nitrogen