Sensitivity of Blood Plasma and Liver Vitamin A Concentrations and Vitamin A Depletion Time to Carotene and/or Vitamin A Intake

Abstract

Summary Blood plasma vitamin A concentrations and liver vitamin A concentrations obtained at slaughter, upon the completion of a carotene and/or vitamin A supplement feeding period and vitamin A depletion time (the weeks required for the blood plasma vitamin A level to decrease to 4.0 γ/100ml., when only a vitamin A depletion ration was fed upon completion of the supplement feeding), were obtained from five experiments. In four of these, Holstein calves previously partially depleted of their vitamin A stores were fed carotene intakes ranging from 12 γ to 540 γ per lb. live weight per day and/or vitamin A intakes ranging from 2.0 γ to 62.5 γ for periods of either 12 or 16 wk. In the fifth experiment, Hereford steers previously grazing native grass pasture were fed intakes of vitamin A from 5.8 to 116.0 γ for a period of 40 wk. The following results were obtained: (1)Average coefficients of variation across all experiments were 19.4% for plasma vitamin A, 9.2% for log (liver vitamin A), and 18.6% for vitamin A depletion time. Thus, log (liver vitamin A) exhibited a smaller experimental error as a percentage of its mean than either plasma vitamin A or vitamin A depletion time. (2)Average sensitivities of these criteria to carotene or vitamin A intake, which was defined as the ratio of the linear slope of the response criteria on intake to the standard deviation of the criterion, Mandel and Stiehler (10), was 4.6 for plasma vitamin A on log (intake), 7.8 for log (liver vitamin A) on log (intake), and 0.1 for vitamin A depletion time on actual intake. Calculation of the sensitivity of vitamin A depletion time in terms of log (intake) gave a range of sensitivities between 0.3 and 23.9, which increased with the intake level. Depletion time was calculated to become more sensitive than plasma vitamin A at carotene intakes of greater than 110 γ and vitamin A intakes of greater than 18 γ, and more sensitive than log (liver vitamin A) at carotene intakes of greater than 126 γ and at vitamin A intakes of greater than 22 γ.