Effect of dietary vitamin A on plasma and liver carotenoid concentrations and fat colour in Angus and Angus crossbred cattle

Abstract

The effect of dietary vitamin A supplements on plasma carotenoid (PC), liver B-carotene, and fat carotenoid concentrations, and on fat colour in cattle were determined in three experiments. In Experiment 1, thirteen 2-year-old Angus × Friesian steers were grazed on pasture, and 6 of the steers were supplemented daily with 1 × 10 6 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 × 10 6 IU and 5 with 2.5 × 10 6 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 × 10 6 or 0.5 × 10 6 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 × 10 6 IU vitamin A caused a linear decrease in PC concentration of 0.13-0.20 µg/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 µg/ml, but in Experiment 3 where steers were fed a low carotenoid diet the decrease was only 0.8-1.0 µg/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 P-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 µg/ml), and because the PC concentration was already low in Experiment 3 (under 2 µg/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 µg/ml.

Effects of vitamin A on growth performance and carcass quality in steers

“…At the beginning of the study, the blood levels of retinol and its precursor, β-carotene, were satisfactory based on Hoffman-La Roche standards as the animals had been grazing pastures abundant in carotenoids prior to the trial. The levels were in the range of those reported in other studies (Cetinkaya and Ozcan, 1991;Knight et al, 1996). After approximately 28 days from the feedlot entry, plasma retinol levels rose and stayed high in both groups for approximately 50 days, while the levels of β-carotene rapidly fell to almost non-detectable levels.…”

Presence of fed β-carotene in digesta, excreta, blood, and hepatic and adipose tissues of Holstein steers

“…The retinol concentrations observed in serum were higher than those reported by Yang et al (1992) with animals grazing during the late wet season on a summer-autumn pasture, but similar to those found by Westendorf et al (1990) and Knight et al (1996) in animals that were supplemented with vitamin A. Figure 2 shows a linear (P < 0.01) response in serum β-carotene to the 30-d supplementation.…”

Características físico-químicas e sensoriais da carne de cordeiros terminados com dietas contendo cana-de-açúcar ou silagem de milho e dois níveis de concentrado

“…Segundo Knight et al (1996), as dietas com baixo teor de carotenoides, como grãos, feno e silagem, propiciam redução da cor amarela da gordura de bovinos, em função da diluição da cor da gordura. Prache et al (2003a) reportaram ainda que a intensidade da absorção de luz pelo carotenoide armazenado na gordura de cordeiros em confinamento foi negativamente correlacionada ao período de confinamento, comprovando que este efeito é mediado pela diluição da gordura de coloração branca (Prache et al, 2003b).…”