EVIDENCE OF MULTIPLE METABOLIC ROUTES IN VANADIUM EFFECTS ON LAYERS -ASCORBIC-ACID DIFFERENTIAL-EFFECTS ON PREPEAK EGG-PRODUCTION PARAMETERS FOLLOWING PROLONGED VANADIUM FEEDING

The development of V toxicity was followed over a 28-d period in 25-wk -old Leghorn layers fed 20 mg ammonium metavanadate/kg diet (Days 1 to 14) followed by 30 mg/kg diet (Days 15 to 28). Then, over a second 28 -d period, the responses to V and supplemental ascorbic acid (AA) fed at 500 or 1,000 mg/kg-diet (Days 29 to 42) followed by 1,500 or 3,000 mg/kg diet (Days 43 to 56) were examined. Feed consumption, egg weight , Haugh units (HU), and BW measurements indicated that the response to V was multifactorial, but of differing intensities and time-frames fo r the variables. Haugh units were lowered rapidly (3 d, P < .05) in re sponse to V feeding, but HU values decreased only slightly when dietar y V was increased to 30 mg/kg. In contrast, egg production was decreas ed moderately by 20 mg V/kg and a considerable further reduction in eg g production resulted from increasing the V to 30 mg/kg. Ascorbic acid supplementation differentially affected these responses: BW, egg prod uction, and egg weight were improved significantly in the V-fed group receiving an AA supplement, as compared with those fed V only. Haugh u nit values, however, were not improved by AA supplementation in groups receiving V. Foam functional properties, which also were changed by V feeding, were not corrected by AA feeding. The results suggest that t he toxic effects of V are mediated through more than one physiological mechanism. One mechanism, which includes negative effects on BW, egg production, and egg weight, is responsive to the additional reducing e quivalents provided by supplemental AA. Another mechanism, which is ap parent from the effect of V on egg HU values, is not ameliorated by AA supplementation after toxicity developed.