title: True absorption of calcium and phosphorus from alfalfa and corn silage when fed to lactating cows.
abstract: A crossover experimental design with an extra period was used with four lactating cows (645 kg BW) and two diets to measure the true absorption of Ca and P from alfalfa hay and corn silage. True absorption was calculated after dosing cows intravenously with 45Ca and 32P to measure endogenous fecal losses. In alfalfa hay and alfalfa-corn silage diets, the Ca and P that came from the hay or hay and silage fraction was 94 and 98% and 63 and 84%, respectively. Cows ate more DM (22.7 vs. 20.6 kg/d) and produced more FCM (35.2 vs. 32.0 kg/d) when consuming alfalfa-corn silage compared with alfalfa hay. True absorption of Ca from alfalfa-corn silage was greater (42.2%) than from alfalfa hay (24.6%). Partial true absorption of Ca from alfalfa hay was 23.5% and from corn silage 51.5%. True P absorption for total diet was similar for both alfalfa hay (64.4%) and alfalfa-corn silage (74.6%). Partial true absorption of P from alfalfa hay (67.3%) was different from that from corn silage (80.0%). Fecal endogenous Ca excretion was nearly double the value (31 vs. 16 mg/kg BW) currently used by NRC. True absorption of Ca from alfalfa was lower and from corn silage was higher than currently used in NRC feeding standards. True absorption of P was higher than values currently used by NRC.
authors.affiliation: USDA Agricultural Research Service, Missouri Cluster, US Dairy-Forage Center, University of Missouri, Columbia 65211.
authors.forename: F A
authors.initials: FA
authors.lastname: Martz
authors.forename: A T
authors.initials: AT
authors.lastname: Belo
authors.forename: M F
authors.initials: MF
authors.lastname: Weiss
authors.forename: R L
authors.initials: RL
authors.lastname: Belyea
authors.forename: J P
authors.initials: JP
authors.lastname: Goff
mesh_terms: D000821:Animal Feed; D000818:Animals; D002117:Calcitriol / Q000097:blood; D002136:Calcium, Dietary / Q000032:analysis / Q000378:metabolism*; D002417:Cattle / Q000502:physiology*; D005260:Female; D006909:Hydroxyproline / Q000097:blood; D007408:Intestinal Absorption / Q000502:physiology*; D000455:Medicago sativa; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism*; D011897:Random Allocation; D012820:Silage; D003313:Zea mays
chemical_list: D002136:Calcium, Dietary; D010758:Phosphorus; D002117:Calcitriol; D006909:Hydroxyproline