Effect of dose and frequency of vitamin A supplements, and carryover effects on plasma carotenoid concentration in steers

Abstract

Experiments were carried out to determine the effect on plasma carotenoid (PC) concentration of dose, frequency of dietary supplements, and the carryover effect once vitamin A supplements ceased. Plasma cholesterol (PChol) concentration and fat colour were also measured in one experiment. Pasture‐fed Angus and Simmental crossbred steers received 1 kg per head per day of pellets fed from troughs in the paddock and vitamin A was included in the pellets when required. Vitamin A supplements decreased PC concentration but there were no differences between doses. Liver vitamin A concentration increased as the dose increased. There were no effects on fat colour despite vitamin A supplements decreasing PC concentration by 30–50%. There were positive correlations between PChol concentration and fat colour, but pre‐treatment PC concentrations provided a better indication of fat colour. All frequencies of vitamin A supplements decreased PC concentration but daily supplements were more effective. After 35 days with daily supplements, PC concentration had decreased 71% compared with a decrease of 46–49% when supplements were given every 2–4 days. The PC concentration in vitamin A‐supplemented steers rapidly increased after supplements ceased but significant differences still remained after 11 weeks.

Keywords:

• cattle plasma carotenoids
• vitamin A supplement
• liver vitamin A
• fat colour