Effect of chromium source on tissue concentration of chromium in pigs.

The concentration of Cr in several tissues in response to high-level, short-term supplementation was used to determine the relative bioavailability among 4 organic Cr sources and to assess the relative safety of high levels of supplementation. Crossbred pigs (n = 40; mean BW = 48.1 +/- 0.9 kg) were allotted to 5 diets: a control diet with no added Cr, or 5,000 microg/kg of Cr from Cr tripicolinate (CrTP), Cr propionate (CrPrp), Cr methionine (CrMet), or Cr yeast (CrY). Twenty gilts were housed individually and barrows were housed in pairs. Average duration of feeding before slaughter was 75 d. For the total experiment, pigs fed the unsupplemented diet had less ADG than pigs fed CrY (P < 0.05). Serum clinical chemistry values, obtained during the final week of the experiment, demonstrated few effects with no responses that would raise concern about metabolic changes in response to the Cr sources. The effects of the forms of Cr fed on carcass measurements and meat quality were also minimal. All Cr sources reduced cooler shrink (P < 0.05) and most resulted in some meat color change on d 1 postslaughter. For tissue Cr content, 4 of 5 tissues (bone, kidney, liver, and ovary) were increased (P < 0.05) in Cr content by supplementation with CrTP and CrMet, whereas only 2 tissues (bone and kidney) were increased (P < 0.05) by CrY, and none were increased by CrPrp. In all tissues of response, CrTP exceeded CrMet and CrMet exceeded CrY. Comparing the relative increase in tissue Cr for all responsive tissues (bone, kidney, liver, and ovary) gave a range of responses, for which the mean bioavailability relative to CrTP across tissues was 13.1% for CrPrp (0.2 to 19.0%), 50.5% for CrMet (36.2 to 79.1%), and 22.8% for CrY (2.5 to 47.9%). In summation, these results show very clear Cr effects on multiple tissues, which is conclusive evidence of absorption and deposition. The lack of a negative response in growth performance, carcass measures, and clinical chemistry at the increased quantities used herein provides assurance that normal quantities of addition are extremely safe.