New Zealand Journal of Agricultural Research abstracts
Effect of dietary vitamin A on plasma and liver carotenoid concentrations and
fat colour in Angus and Angus crossbred cattle
T. W. KNIGHT1
A. F. DEATH1
P. D. MUIR2
M. RIDLAND1
T. K. WYETH1
1AgResearch Grasslands
Private Bag 11008
Palmerston North, New Zealand
2AgResearch
Poukawa Research Farm
P.O. Box 8144
Havelock North, New Zealand
Abstract The effect of dietary vitamin A supplements on
plasma carotenoid (PC), liver ß-carotene, and fat carotenoid
concentrations, and on fat colour in cattle were determined in three
experiments. In Experiment 1, thirteen 2-year-old Angus x Friesian steers were
grazed on pasture, and 6 of the steers were supplemented daily with 1 x
106 IU vitamin A for 83 days. In Experiment 2, twenty 2-year-old
Angus crossbred heifers were grazed on pasture with 5 being supplemented daily
with 1 x 106 IU and 5 with 2.5 x 106 IU vitamin A for 31
days. Cattle in Experiments 1 and 2 were slaughtered at the end of the
experiments, and liver and fat samples were analysed for retinol and carotenoid
concentrations respectively in Experiment 1, and liver samples were analysed
for both retinol and carotenoid concentrations in Experiment 2. Experiment 3
involved ninety 3-year-old Angus steers, 10 of which were slaughtered at the
beginning of the experiment, 20 were grazed on pasture, and the remaining 60
steers were fed a diet of 70% barley and 30% pasture-silage on a feedlot either
without vitamin A supplement, or with a supplement of 1 x 106 or 0.5
x 106 IU vitamin A daily. Ten steers from each group were
slaughtered after 62 days and the other 10 after 104 days of treatment. Daily
supplements of 1 x 106 IU vitamin A caused a linear decrease in PC
concentration of 0.13-0.20 ug/ml per day for about 30 days. In Experiments 1
and 2, this represented a reduction of about 40-50% in PC concentration,
equivalent to a decrease of 4.2-6.4 ug/ml, but in Experiment 3 where steers
were fed a low carotenoid diet the decrease was only 0.8-1.0 ug/ml. PC
concentrations in Experiments 2 and 3 were not affected by either the dose of
vitamin A or the decline in pasture carotenoid concentration over the duration
of the experiments. Vitamin A supplementation reduced the liver
[[beta]]-carotene concentration by 40-48%, and increased the retinol
concentration. Subcutaneous fat colour and carotenoid concentration were not
affected by vitamin A supplements in any experiment, possibly because PC
concentration was still too high in Experiment 1 (5-7 ug/ml), and because the
PC concentration was already low in Experiment 3 (under 2 ug/ml). These
experiments suggest that for vitamin A to be effective in reducing fat colour,
the initial PC concentration may need to be less than 6-7 ug/ml.
Keywords fat colour; plasma carotene; cattle; vitamin A
New Zealand Journal of Agricultural Research, 1996, Vol. 39: 281-292
0028-8233/96/3902-0281 $2.50/0 (c) The Royal Society of New Zealand
1996
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