Influence of supplemental, dietary vitamin A on retinol-binding protein concentrations in the plasma of preruminant calves.
Transport of retinol (vitamin A alcohol) from retinoid stores in the liver to target tissues is accomplished exclusively by a specific plasma protein, retinol-binding protein. Within individuals, retinol-binding protein concentrations in plasma are regulated and remain constant except in extremes of vitamin A nutriture or in disease. In the present study, retinol-binding protein concentrations in plasma from preruminant calves supplemented with 0, 1700 (i.e., current NRC requirement), 34,000, or 68,000 IU of vitamin A daily from birth to 27 d of age (n = 6/treatment) were quantified. Retinol-binding protein concentrations at birth averaged 21 microg/ml (n = 24) or approximately 50% of concentrations in dairy heifers and cows. Plasma retinol and retinol-binding protein concentrations were correlated positively, corroborating the role of vitamin A nutriture in the regulation of retinol-binding protein secretion from the liver. In this regard, dietary vitamin A influenced positively retinol and retinol-binding protein concentrations and, as a consequence, the degree of saturation of retinol-binding protein with retinol. At 27 d of age, calves fed > or = 34,000 IU of vitamin A had substantially higher retinol and retinol-binding protein concentrations than did calves fed < or = 1700 IU of vitamin A, indicating that dietary vitamin A effects positively vitamin A status. The data also suggest that the current NRC requirement may not be sufficient to assure vitamin A adequacy in preruminant calves. Percent saturation of retionol-binding protein with retinol in all calves was < 35%, much lower than anticipated and suggests that the retinol requirement of vitamin A-responsive tissues exceeded vitamin A availability.
Nonnecke
B J
BJ
Periparturient Diseases of Cattle Research Unit, USDA, ARS, National Animal Disease Center, Ames, IA, 50010-0070, USA. bnonnecke@nadc.ars.usda.gov
Roberts
M P
MP
Godkin
J D
JD
Horst
R L
RL
Hammell
D C
DC
Franklin
S T
ST
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D002417:Cattle; D005260:Female; D008099:Liver / Q000378:metabolism*; D009751:Nutritional Requirements; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D054839:Retinol-Binding Proteins, Plasma; D014801:Vitamin A / Q000008:administration & dosage* / Q000097:blood* / Q000378:metabolism
D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma; D014801:Vitamin A