Abstract
In order to estimate the availability of ruminally-protected Lys (RPLys) and Met (RPMet), quantitative changes of free Lys and Met in the total abomasal outflow and feces were determined in three Holstein heifers with a T-shaped duodenal cannula. RPLys was prepared by coating Lys with fat and RPMet with a pH-sensitive polymer. RPLys and RPMet containing 30 g of each amino acid were supplied together to heifers, and total abomasal outflow was collected hourly from the T-shaped duodenal cannula for a 48 h period. Collected abomasal outflows were fractionated into liquid and solid phases to measure free Lys and Met concentration. At 2 wk after total abomasal outflow sampling, heifers were supplied RPLys and RPMet together again, and total feces were collected every 12 h for a 3 d period to estimate excreted RPLys and RPMet in feces. The amounts of Lys and Met recovered from the liquid fractions of abomasal outflow were estimated to be 23.9±8.3% and 68.6±3.6% (p=0.008) of RPLys and RPMet ingested, respectively. Final intestinal disappearances of Lys and Met were estimated to be 49.5±2.6% and 78.2%±6.5% (p=0.015) of ingested RPLys and RPMet, respectively. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 4 : 549-554)
Highlights
Recent advances in amino acid nutrition for lactating dairy cattle have interested the feed industry in the production and usage of ruminally-protected amino acids (RPAA)
RPAA are designed as crystal forms of amino acids to escape degradation by rumen microorganisms and to deliver eligible amino acids for effective absorption in the small intestine, and are used for improvement of animal production
Several technological approaches have focused on the development of ruminally-protected Lys (RPLys) and Met (RPMet) since both of these amino acids are liable to be limiting in dairy cattle (NRC, 2001)
Summary
Recent advances in amino acid nutrition for lactating dairy cattle have interested the feed industry in the production and usage of ruminally-protected amino acids (RPAA). RPAA are designed as crystal forms of amino acids to escape degradation by rumen microorganisms and to deliver eligible amino acids for effective absorption in the small intestine, and are used for improvement of animal production. It is well accepted that feeding of RPLys and RPMet is effective in increasing milk yield in dairy cattle It is laborious and time-consuming to establish the effect of dietary amino acids on the performance of milking cattle. It is expected that intestinal availability of RPAA can be estimated in vivo on the basis of disappearance of free amino acids in the intestine by measuring recovery of all amino acids in the abomasal digesta collected from a cannula in the duodenum and in the excreted feces. T-shaped duodenal cannula by measuring recovery of free amino acids in duodenal digesta and feces
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