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True Absorption of Calcium and Phosphorus from Alfalfa and Corn Silage When Fed to Lactating Cows

USDA Agricultural Research Service, Missouri Cluster, US Dairy-Forage Center, University of Missouri, Columbia 65211
National Animal Disease Center, Ames, IA 50010

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.

This article has been cited by other articles:

				W. P. Weiss and D. J. Wyatt Macromineral Digestion by Lactating Dairy Cows: Estimating Phosphorus Excretion via Manure J Dairy Sci, July 1, 2004; 87(7): 2158 - 2166. [Abstract] [Full Text] [PDF]