Relationship between nyctalopia and plasma vitamin A levels and the effect of vitamin A supplementation in beef calves

Abstract

Two groups of Hereford calves with a prior history of low plasma vitamin A levels and nyctalopia were fed sorghum grain ad lib. from 16 to 20 weeks of age. One group was supplemented with vitamin A by drenching.
Plasma vitamin A levels of 8 μg/100 ml or less were associated with nyctalopia. Calves recovered from nyctalopia within a week of vitamin A administration.
A difference in light intensity sufficient to influence the onset of nyctalopia was evident in a time interval of 10 min between successive runs through a maze.
There were no significant differences in blood haemoglobin, packed cell volume and white cell count between vitamin A deficient and supplemented calves.
Grain consumption was higher in the supplemented group, being 5 · 49 lb per head per day compared with 4·20 lb for the control group. The mean body-weight gain was 5·5 ± 0 · 8 and 3·1 ± 0 · 8 lb per week for the supplemented and control group respectively.