Effects of dietary protein level and level of feed intake on the apparent bioavailability of selenium for the chick.

Experiments were conducted to determine the effects of dietary protein level and level of feed intake on the apparent bioavailability of Se from Na2SeO3 and selenomethionine (DL-Se-Met) for protection from exudative diathesis (ED) of the Se- and vitamin E-depleted chick. Level of dietary protein (22.5 vs. 16.9%) significantly (P less than .01) affected the incidence of ED at several levels of dietary Se from each source. At each level of Se, the low protein diet resulted in a lower incidence of ED and, thus, an increase in the apparent bioavailability of Se; Se from Na2SeO3 was more available than that from Se-Met. Further experiments were conducted to determine whether the effect of dietary protein level on the incidence of ED was due to effects on growth rate or feed intake. Chicks were fed the high or low protein basal diets at 75% of ad libitum rate of feed consumption. Sodium selenite was added to make Se intakes equivalent, either on a per day or a per unit gain basis, to ad libitum feeding controls receiving the Se-supplemented diets. Results showed that both a low level of dietary protein and a restricted level of feeding markedly reduced the incidence and severity of ED. The activity of Se-dependent glutathione peroxidase (SeGSHpx) in plasma and liver varied inversely with the incidence of ED and was increased by feed restriction. These results suggest that growth rate affects both the clinical and biochemical manifestations of Se-deficiency in the chick. Because both parameters are used to assess the bioavailability of Se in feeds and foods, bioassays in which growth rate is different between test and reference treatments may yield incorrect results.