Vitamin A and protein interrelationships in the milk-fed lamb.

I . The mean liver retinol reserve (retinal+ retinyl esters, expressed as retinol) of six newborn lambs was 21 ? 8 pg. The mean value for ten suckled lambs, aged 5-7 days, was 2655 +47z pg retinol per liver. 2. Three unsuckled lambs were fed ad lib. from birth for 28 days on a high-protein diet, based on lard and skim milk, without supplementary vitamin A. The diet provided sufficient vitamin A for normal growth, but insufficient to permit substantial liver reserves (43 8 pg retinol per liver). 3. Thirty-six suckled lambs aged 5-7 days were given either a lowor a high-protein diet for ZI days, with or without graded levels of retinyl acetate or &carotene. There were no significant differences in the live-weight gain or in liver retinol reserves between the lowand highprotein dietary treatments, or between the supplemented and unsupplemented groups. 4. Twelve lambs were pair-fed on either a lowor a high-protein diet from birth for PI days. Six lambs that were given a large supplement of retinyl palmitate on the 1st day of life had stored significantly less retinol in the liver at 21 days (P < 001) than six lambs given a somewhat smaller total amount of retinyl palmitate in small daily doses. Lambs given the high-protein diet had significantly greater liver retinol reserves ( P < 0.01) than lambs given the low-protein diet, with both methods of supplementation. 5. Twelve lambs were pair-fed from birth on a high-protein diet for z or 6 days. Lambs that were given retinyl palmitate dissolved in either a lowor a high-protein diet on the 1st day of life had significantly lower liver retinol reserves some 24 h later ( P < 0.01) than lambs given similar treatments on the 5th day of life. Liver retinol reserves were positively correlated with the protein concentration of the diet at the time of supplementation. 6. Eighteen lambs were pair-fed from birth with either a lowor a high-protein diet. Six pairs were given retinyl palmitate daily and three pairs were given the supplement 48 h before slaughter. The source of protein was casein. Eight out of nine lambs given the low-protein diet would have died had they not been slaughtered at between 8 and I X days of age. The time of supplementation had no significant effect on liver retinol reserves, which were very low, regardless of the dietary protein concentration. Lambs given the high-protein diet retained a significantly greater proportion (P < 005) of the dietary retinyl palmitate than lambs given the low-protein diet.