Morphologic alterations in small intestinal epithelium of lambs fed vitamin A-depleted diet.

Ten crossbred wether lambs were fed once daily an oat diet that contained 3102 micrograms of retinyl palmitate (control) and were supplemented with 55,000 micrograms of retinyl palmitate orally once every two weeks. Twenty lambs were fed the same oat diet without retinyl palmitate supplements (A-depleted). After being fed the A-depleted diet for 28 weeks, 10 A-depleted lambs were repleted by feeding the control diet and oral supplementation of retinyl palmitate for eight weeks. The A-depleted lambs had serum vitamin A concentrations indicative of vitamin A deficiency, which was supported by very low liver vitamin A concentrations. Light microscopic and ultrastructural examinations revealed that alterations occurred at 50% and 75% of the small intestine length in A-depleted lambs only. Sawtooth configuration of the intestinal epithelium was a distinctive histologic feature. Consistent ultrastructural alterations were vesicular microvillar degeneration and disruption of the capillary endothelium. These results suggests that A-depleted diets have a detrimental effect on the small intestinal epithelium of lambs. Vitamin A repletion appears to minimize the detrimental effects.

Vitamin A deficiency: serum cortisol and humoral immunity in lambs.

Serum cortisol and antigen-specific and polyclonal immunoglobulin G (IgG) concentrations were measured to investigate the relationship between vitamin A status and immune function in lambs. Twenty-four 3-mo-old crossbred ewe lambs weighing approximately 10 kg were each fed 900 g/d of a carotene-deficient diet. The 12 control lambs also received a 100,000 IU oral dose of vitamin A palmitate every 2 wk. All lambs were given primary and secondary antigenic challenges. Lambs were slaughtered at the end of the secondary challenge period. Liver vitamin A concentrations were greater (P less than .001) in the control animals (69.5 vs 1.3 micrograms/g wet tissue). Both groups of lambs exhibited a similar growth response until d 105, after which daily gain of the control lambs exceeded (P less than .03) that of the A-deficient lambs. Polyclonal serum IgG concentrations were greater (P less than .05) in the A-deficient lambs on d 49 to 124 and on d 151 (P less than .10). Ovalbumin-specific serum IgG concentrations tended to be greater in the control lambs throughout the primary and secondary challenge periods. Control lambs had greater titers on d 164 (P less than .07) and d 190 (P less than .03). Vitamin A status appeared to have no consistent effects on serum cortisol concentrations. Spleen weights were greater (P less than .002) in the A-deficient lambs. Lungs from 11 of 12 A-deficient lambs contained abscesses, as opposed to 1 of 12 for the control lambs. Both polyclonal and antigen-specific IgG concentrations were affected by vitamin A status. Serum cortisol concentrations did not appear to mediate this effect.