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Vitamin a Activity of Carotenes in Corn Silage Fed to Lambs¹

Department of Animal Husbandry, Michigan State University, East Lansing, Michigan

This study was conducted to compare the biopotency of the carotenes in corn silage with all-trans-retinyl palmitate for purposes of supporting liver vitamin A storage when fed to sheep. Fifty-six Western lambs with an average initial weight of 22.6 kg were fed a pelleted vitamin A depletion diet ad libitum for 110 days. Initial serum vitamin A levels of 28.3 µg/100 ml dropped to 20.0 µg/100 ml at the end of depletion. The lambs were allotted at random to 1 of 4 repletion diets. Lot 1 received corn silage ad libitum plus 0.16 kg/lamb/day of a protein-mineral-vitamin supplement. The total carotene content of the corn silage was 8.1 mg/kg (fresh basis, 28% dry matter). Lots 2, 3 and 4 received the modified depletion diet (90% dry matter) supplemented with 0.52, 1.55 and 4.65 mg of all-trans-retinyl palmitate/kg, respectively. After 70 days of repletion, serum vitamin values were 41.6, 20.4, 40.2 and 48.3 µg/100 ml for lots 1 through 4, respectively. Final liver vitamin A values (milligrams per liver), in the same order, were 12.29, 1.92, 8.35 and 15.36. The linear regression of total liver vitamin A stored with daily dietary intake of retinyl palmitate was calculated to be = 1.6038 + 1.4516X, where = mg vitamin A/liver and X = mg of all-trans-retinyl palmitate ingested/lamb/day. Using this regression and interpolating from liver vitamin A storage when corn silage was consumed, it was established that 1 mg of corn silage carotenes was equivalent to 0.24 mg (436 IU) of all-trans-retinyl palmitate.

² Present address: College of Veterinary Medicine, National Autonomous University of Mexico, Mexico City, D. F.

³ Present address: Area Extension Center, Ohio State University, Fremont, Ohio.

Manuscript received 7 February 1968.