Martz F A, Belo A T, Weiss M F, Belyea R L, Goff J P
USDA Agricultural Research Service, Missouri Cluster, US Dairy-Forage Center, University of Missouri, Columbia 65211.
J Dairy Sci. 1990 May;73(5):1288-95. doi: 10.3168/jds.S0022-0302(90)78794-2.
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.
采用交叉实验设计并增加一个周期，使用四头泌乳奶牛（体重645千克）和两种日粮来测定苜蓿干草和玉米青贮中钙和磷的真消化率。给奶牛静脉注射45Ca和32P以测定内源性粪钙损失后，计算真消化率。在苜蓿干草和苜蓿-玉米青贮日粮中，来自干草或干草与青贮部分的钙和磷分别为94%和98%，以及63%和84%。与苜蓿干草相比，奶牛采食苜蓿-玉米青贮时采食的干物质更多（22.7对20.6千克/天），产奶量也更高（35.2对32.0千克/天）。苜蓿-玉米青贮中钙的真消化率（42.2%）高于苜蓿干草（24.6%）。苜蓿干草中钙的部分真消化率为23.5%，玉米青贮中为51.5%。苜蓿干草（64.4%）和苜蓿-玉米青贮（74.6%）的总日粮磷真消化率相似。苜蓿干草（67.3%）和玉米青贮（80.0%）的磷部分真消化率不同。粪内源钙排泄量几乎是美国国家研究委员会（NRC）目前使用值（31对16毫克/千克体重）的两倍。苜蓿中钙的真消化率低于NRC饲养标准中目前使用的值，而玉米青贮中钙的真消化率更高。磷的真消化率高于NRC目前使用的值。
