No abstract

Behavior, physiology, health, egg production, and egg quality characteristics of laying hens housed either 1/1394-cm2 cage (S), 2/1394-cm2 cage (HD), 2/2788-cm2 cage (LD), or in floor pens (P), each containing 25 hens, were monitored in order to assess hen welfare in different management systems. Egg production was highest in P and S hens. There were no differences among treatment groups in feed efficiency, egg weight, or egg taste, although egg shell breaking strengths were lower in HD hens despite their relatively low egg production. Blood spots were most common in eggs from caged hens. With respect to behavior, penned hens locomoted more, spent less time in stationary exploration than caged birds, and utilized nest boxes for activities in addition to egg laying. The HD hens fed less frequently than did the LD, and HD cage pairs engaged less frequently in simultaneous feeding, drinking, and resting behavior than LD pairs. Plasma corticosterone levels were initially found to be higher in pens than cages; this difference disappeared when the use of trap-nesting to capture P birds for sampling was discontinued. Nighttime corticosterone levels were higher in HD hens. In contrast, primary and secondary hemagglutination titers to sheep erythrocyte (SRBC) antigen, heterophil to lymphocyte ratios, hepatic zinc metallothionein, serum zinc, and body weights did not differ among treatments. Mortality, however, was lower in pens. It was concluded that, although there were striking dissimilarities in behavior between the pen and cage environments, physiological and production data did not provide evidence of stress associated with cage housing per se. High density caging, however, may be a stressor; this is discussed with reference to other research.

Tocopherols are known to undergo metabolism to phytyl chain-shortened metabolites excreted in urine. We sought to characterize the pathway, including associated enzymes, involved in this biotransformation. We previously found that human hepatoblastoma (HepG2) cultures metabolized tocopherols to their corresponding short-chain carboxychromanols. Putative metabolites of gamma-tocopherol that contained intact chromanol moieties were structurally identified using HepG2 cultures and electron impact gas chromatography-mass spectrometry. A microsomal assay for synthesis of the initial omega-oxidation metabolites was developed and used to screen several recombinant human liver cytochrome P450 isozymes for omega-hydroxylase activity. Seven metabolites of gamma-tocopherol were identified in HepG2 cultures, including 13'-hydroxy-gamma-TOH and all six carboxychromanols predicted by sequential omega-oxidation truncation. Rat and human liver microsomes catalyzed synthesis of 13'-OH- and 13'-COOH-gamma-TOH, but not other metabolites, in the presence of NADPH. Inclusion of NAD favored synthesis of the 13'-COOH metabolite. Recombinant CYP4F2, but not other major human liver CYP isoforms (including CYP3A4 and 3A7), exhibited tocopherol-omega-hydroxylase activity. Liver microsomes and recombinant CYP4F2 both exhibited substrate preference for gamma-TOH over alpha-TOH, and recent studies show that tocotrienols are catabolized more extensively than the corresponding tocopherols. Comparative rates of omega-oxidation of tocochromanols in hepatocytes are inversely related to biopotency and directly related to cytotoxicity of these substances in macrophages. The liver contains a cytochrome P450-mediated pathway that preferentially catabolizes "non-alpha" tocochromanols to excretable metabolites. This metabolic pathway appears central to the optimization of tissue tocochromanol status.

Response of intestinal metallothionein and zinc to dietary zinc intake was investigated in zinc-depleted rats, after a single feeding by stomach tube of a purified diet supplemented with either 125 ppm zinc or less than 1 ppm zinc. Serum zinc concentration was maximal 3 hours post-feeding, then stabilized at lower levels returning to baseline concentration by 18 hours. Mucosal zinc concentration rose to a maximum by 6 hours after feeding and plateaued at slightly lower levels thereafter, due to association of this zinc with metallothionein. The rate of metallothionein synthesis rose 4-fold, 6-9 hours after feeding, coinciding with the maximal contest of translatable metallothionein mRNA concentration. Together, these findings provide strong evidence for a regulatory role of metallothionein in zinc absorption and homeostasis, where dietary zinc influences subcellular events in mucosa affecting regulation of the metallothionein gene. These events include the induction of de novo metallothionein synthesis, preceded by an increase in translatable mRNA specific for this metalloprotein, and followed by a reduction in zinc absorption simultaneous with the binding of absorbed zinc with newly synthesized thionein polypeptides.

Reply to Bonner et al.Dear Editor, Drs. Bronner, Sepchenko, Wood and Pansu have critically evaluated my Issues and Opinion article (1) and make very important points. They are clearly justified in questioning the diffusion value "extrapolated" from two points in the Ireland and Fordtran experiment (2). They (and I) are concerned that the interpretation depends critically on an assumed luminal calcium concentration at which calcium flux (diffusion) is zero (1.5 mmol/L). A subtle change in this value (or in either of the two values presented) drastically changes the slope and the estimate of the diffusion component at higher luminal concentrations. It is intriguing that the values in this study, as well as one conducted 15 y later (3) in which a completely different approach was attempted, were reasonably close when considered at intakes approaching "normal" intakes, i.e., 900 mg/d. As Bronner et al. indicate in their letter, higher diffusion values (percentages) were presented in Table 4 of that study. However, these data were derived from normal individuals consuming a meal containing 502 or 1071 mg of calcium not as indicated in the comments of Bronner et al. as an intake per day. The results shown in that table are consistent with their other data and again indicate that at higher intakes, passive diffusion may constitute a major proportion of calcium absorption; this is not disputed. However, assuming three meals per day, these values represent intakes Ͼ 1.5 g/d. I have no doubt that passive diffusion can ultimately be important, but my focus has always been on "normal" intakes for normal people; I (and perhaps others) remain to be convinced that at normal intakes, passive diffusion is the "major" route of absorption as stated by Bronner et al. in their correspondence.It is interesting that they did not address the ineffectiveness of oral calcium in children who lack the vitamin receptor system (4). In these children, passive diffusion is presumably the only means by which luminal calcium can be absorbed. A diet therapy in which these children consumed Ͼ2 g calcium/d (with lactose) was essentially ineffective. The authors of that study concluded that the high (calcium) lactose regimen given for 6 mo was "well tolerated but its therapeutic action was nil." I have since found a report that indicates that intakes of ϳ6 g/(m 2 ⅐ d) are capable of "maintaining" these children after initial intravenous therapy (5). These authors indicate that "Only after radiologic healing has been observed can oral calcium therapy be introduced." It would appear then that for passive diffusion to provide the required calcium for these children, an extraordinarily large daily intake is necessary. Perhaps this greater than sixfold apparent requirement reflects the inefficiency of passive diffusion. If so, then an estimate of the contribution of passive diffusion of nearly 20% (1) may be too high.A final point raised by Bronner et al. in their letter concerns the relative risk of calcium vs. vitamin D supplements and the regulation o...